Influence of call broadcast timing within point counts and survey duration on detection probabili... more Influence of call broadcast timing within point counts and survey duration on detection probability of marsh breeding birds.
Human-induced effects on lowland conifer forests in hemiboreal regions are increasing because of ... more Human-induced effects on lowland conifer forests in hemiboreal regions are increasing because of expanded use of these northern ecosystems for raw materials, energy, and minerals as well as the potential effects of climatic changes. These forests support many breeding bird species across the Holarctic and allow the persistence of several boreal bird species in hemiboreal and even temperate regions. These bird species are of particular conservation concern as shifting patterns northward in forest composition caused by climate change will likely affect their populations. However, effective management and conservation options are limited because the specifics of these species' breeding habitats are not well understood. We modeled and mapped habitat suitability for 11 species of boreal birds that breed in the lowland conifer forests of the Agassiz Lowlands Ecological Subsection in northern Minnesota and are likely to have reduced breeding habitat in the future: Spruce Grouse (Falcipennis canadensis), Black-backed Woodpecker (Picoides arcticus), Olivesided Flycatcher (Contopus cooperi), Yellow-bellied Flycatcher (Empidonax flaviventris), Boreal Chickadee (Poecile hudsonicus), Goldencrowned Kinglet (Regulus satrapa), Ruby-crowned Kinglet (Regulus calendula), Swainson's Thrush (Catharus ustulatus), Connecticut Warbler (Oporornis agilis), Palm Warbler (Setophaga palmarum), and Dark-eyed Junco (Junco hyemalis). Sets of 7 to 16 potential environmental covariates, including both stand-level and landscape attributes, were used to develop individual species models. Within this lowland conifer-dominated ecosystem, we found significant selection for specific forest and landscape characteristics by all but one of these species, with the best models including between one and nine variables. Habitat suitability maps were developed from these models and predictions tested with an independent dataset. Model performance depended on species, correctly predicting 56-96% of test data. We present a map combining suitability scores for five species of conservation concern that has been used for conservation planning and management opportunities across a broad, lowland forest landscape. We recommend managers utilize the detailed model development and validation framework to address local and regional conservation issues.
Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were ... more Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were compared to invertebrate availability as measured by aerial tow nets. The majority of the biomass in the nestlings' diet was adult insects with larval stages of aquatic origin, while absolute numbers of insects of both aquatic and terrestrial origin were similar. Orders of invertebrates in the diet and available were similar in number but not in biomass. Diet showed little variation by time of day, date of sampling or the age of Manuscript
We established bird monitoring programs in two regions of Minnesota: the Chippewa National Forest... more We established bird monitoring programs in two regions of Minnesota: the Chippewa National Forest and the Superior National Forest. The experimental design defined forest cover types as strata in which samples of forest stands were randomly selected. Subsamples (3 point counts) were placed in each stand to maximize field effort and to assess within-stand and between-stand variation for a variety of bird parameters. Data gathered in 1991 were used to evaluate several assumptions that were made in the experimental design and showed that variance of most bird parameters among strata were similar. This data indicated that a proportional stratified sample by forest cover type was reasonable. We also found that two subsamples per stand would be optimum when a variety of strata types and bird variables were considered. Analyses based on 120 stands in the Chippewa National Forest and 150 stands in the Superior National Forest indicated that a two-tailed t-test could detect a 25 percent change in bird numbers for common species. For most other species, we could detect less than a 50 percent annual change. Monitoring programs within regions should be habitat specific so that changes in bird numbers can be related to: (1) habitat changes that have occurred in the region; (2) natural fluctuations in bird numbers; or (3) other factors.
The Canada Warbler (Cardellina canadensis) is a species of high conservation importance because o... more The Canada Warbler (Cardellina canadensis) is a species of high conservation importance because of its low overall density and long-term widespread population declines on the breeding grounds. Results of previous research on the species suggest that its breeding habitat preferences vary across its range. However, the underlying processes associated with habitat use are unknown. Using a 20 yr dataset, we developed occupancy models for Canada Warblers to determine the influence of habitat characteristics (e.g., understory vegetation, canopy cover), landscape context (e.g., edge, forest patch size), and species co-occurrence on occupancy, colonization, and local extinction parameters. Our results show that multiple habitats are used by Canada Warblers on the breeding grounds; common variables associated with large-scale, long-term occupancy dynamics are forest age, landscape composition at the 100 m and 500 m scales, and mean patch size. Overall, Canada Warblers were nearly twice as persistent in mature forest stands (.80 yr) and large, mixed forest stands. Further, models indicated that species co-occurrence was an important predictor of Canada Warbler occupancy in some cover types. The results of this study increase our understanding of population processes over large, dynamic landscapes and provide essential conservation information to improve habitat and landscape management for the Canada Warbler.
Continental-scale monitoring programs with standardized survey protocols play an important role i... more Continental-scale monitoring programs with standardized survey protocols play an important role in conservation science by identifying species in decline and prioritizing conservation action. However, rare, inaccessible, or spatially fragmented communities may be underrepresented in continental-scale surveys. Data on these communities often come from decentralized, local monitoring efforts that differ in their goals and survey protocols. We combine 16 point count datasets, controlling for differences in protocol and detection probabilities to estimate regional trends for 14 spruce-fir forest bird species across Northeastern and Midwestern United States, a vulnerable community threatened by numerous anthropogenic stressors and widely considered a priority for conservation. Our analyses indicated that four species considered as ecological indicators for this community, Bicknell's Thrush (Catharus bicknelli), Magnolia Warbler (Setophaga magnolia), Blackpoll Warbler (Setophaga striata) and Yellow-bellied Flycatcher (Empidonax flaviventris), each exhibited significant declines. Olive-sided Flycatcher (Contopus cooperi), a species of concern in parts of its range, and two additional species for which no previous concern existed, the Evening Grosbeak (Coccothruastes vespertinus) and the Gray Jay (Perisoreus canadensis), each also showed significant overall declines. Five out of nine species with sufficient data for analyses from Northeastern and Midwestern surveys showed significant differences in trends between these regions. Spruce-fir obligate species were more likely to decline significantly than species that use spruce-fir in addition to other habitat types. These results demonstrate the value of combining disparate data sources for analyzing regional patterns of population trends to confirm and extend conservation concern for some species and identify others for which additional attention may be needed.
Establishing whether conditions are suitable for reproduction would help determine if immigration... more Establishing whether conditions are suitable for reproduction would help determine if immigration is necessary for Canada lynx (Lynx canadensis) to persist at the southern edge of the species range. We located den sites and monitored reproduction of radiocollared lynx in Minnesota from 2004 to 2006. Movement rates of denning females measured with Global Positioning System collars were similar to movement rates of lynx elsewhere. Female lynx with kittens used different habitat types in predenning, denning, and postdenning periods. Landscape composition at the scale of the foraging radius around a den site contained more lowland conifer, upland conifer, and regenerating forest than did home ranges or the area used by radiocollared lynx in Minnesota, USA. We used the spatial distribution of cover-type composition around known den sites to predict and map potential denning habitat in northeastern Minnesota. Techniques for identifying the spatial distribution of suitable denning habitat provide a biological basis for management actions that could enhance recovery of Canada lynx populations in the southern part of the species range.
Questions: Two alternative mechanisms of abrupt vegetation change across ecological boundaries ha... more Questions: Two alternative mechanisms of abrupt vegetation change across ecological boundaries have been proposed: (1) concomitantly abrupt gradients in physical environmental variables and vegetation across the boundary, and (2) gradual environmental gradients that vegetation responds to in a non-linear or threshold manner. Here, we evaluate spatial patterns of climate and vegetation across a grassland-forest biome boundary to examine evidence in favour of either of these alternatives. Location: Minnesota, USA. Methods: Vegetation data represented the presence of prairie vs. forest vegetation in Minnesota from 1847 to 1908, generally prior to European settlement of the region, while the climatic variables represented an index of long-term average moisture availability (precipitation minus potential evapotranspiration (P-PET). Using linear and sigmoidal regression models, we evaluated spatial patterns of change in vegetation, climate and vegetation-climate relationships across 22 transects (170-400 km) oriented perpendicular to the biome boundary. We also evaluated boundary characteristics in light of dominant topographical controls and position along the boundary. Results: Vegetation followed a sigmoidal pattern of change across the boundary, with mean boundary width of ca. 100 km. The P-PET increased by ca. 100 mm across the boundary following a comparatively smooth pattern of change. Climate-vegetation relationships were clearly non-linear across the boundary, indicating these variables did not change in a common spatial pattern. Regional topographical controls modified relationships between vegetation and climate along the length of the boundary. Conclusions: Our results document strong non-linear relationships between the presence of forest vegetation and its dominant climate control across a grassland-forest biome boundary. An average change of ca. 100 mm in P-PET moving across the boundary is about 40% of the long-term mean annual range of this variable, suggesting that modest changes to P-PET may potentially cause substantial shifts in the location of the prairie-forest boundary.
Each autumn, tens of thousands of raptors pass over Hawk Ridge in Duluth, Minnesota, on their sou... more Each autumn, tens of thousands of raptors pass over Hawk Ridge in Duluth, Minnesota, on their southbound migration, but migratory pathways leading to Hawk Ridge are unknown. To address this issue, we counted migrating raptors between mid-August and mid-November 2008 from 24 observation points along eight transects perpendicular to the shoreline between Duluth and the Minnesota-Canadian border. Our goals were to determine migratory pathways over a large area (.2000 km 2) and identify how these movements were affected by weather, time of day, season, and characteristics of the landscape. A total of 4303 raptors of 14 different species were counted during the 2008 migration season. Exploratory analyses suggested that migratory raptors concentrated near the northern shoreline of Lake Superior, particularly during midday when winds are westerly. Average migration height differed between soaring raptors (buteos and eagles) and accipiters, with .40% of soaring raptors observed higher than 100 m above the tree canopy and $30% of accipiters observed lower than 100 m above the tree canopy. Mixed models analysis identified the significant factors (P , 0.05) associated with total raptor migration: wind direction, time of day, temperature, and antecedent wind (number of days in which the wind did not have a westerly component prior to the observation days; R 2 5 0.23). Significant factors associated with soaring-raptor migration included wind direction, time of day, temperature, and seasonal interval (e.g., early or late in the migration season; R 2 5 0.17) and those associated with accipiter migration included time of day, temperature, antecedent wind, wind direction, and seasonal interval (R 2 5 0.29). With the increasing popularity of wind power development, information is needed regarding avian migratory pathways to avoid bird-turbine conflicts. The methodology and design of this study provided a means to quantify the magnitude, timing, pathways, and weather conditions associated with raptor migration over a large landscape.
Space use and movements of Canada lynx (Lynx canadensis) are difficult to study with very-high-fr... more Space use and movements of Canada lynx (Lynx canadensis) are difficult to study with very-high-frequency radiocollars. We deployed global positioning system (GPS) collars on 11 lynx in Minnesota to study their seasonal space-use patterns. We estimated home ranges with minimum-convex-polygon and fixed-kernel methods and estimated core areas with area/probability curves. Fixed-kernel home ranges of males (range ¼ 29-522 km 2) were significantly larger than those of females (range ¼ 5-95 km 2) annually and during the denning season. Some male lynx increased movements during March, the month most influenced by breeding activity. Lynx core areas were predicted by the 60% fixed-kernel isopleth in most seasons. The mean core-area size of males (range ¼ 6-190 km 2) was significantly larger than that of females (range ¼ 1-19 km 2) annually and during denning. Most female lynx were reproductive animals with reduced movements, whereas males often ranged widely between Minnesota and Ontario. Sensitivity analyses examining the effect of location frequency on homerange size suggest that the home-range sizes of breeding females are less sensitive to sample size than those of males. Longer periods between locations decreased home-range and core-area overlap relative to the home range estimated from daily locations. GPS collars improve our understanding of space use and movements by lynx by increasing the spatial extent and temporal frequency of monitoring and allowing home ranges to be estimated over short periods that are relevant to life-history characteristics.
Nest predation has been identified as the primary mechanism contributing to reduction of reproduc... more Nest predation has been identified as the primary mechanism contributing to reduction of reproductive success for the marsh-breeding red-winged blackbird (Agelaius phoeniceus). Differences in rates of nest predation have been linked to nest site characteristics within a wetland, primarily water depth. However, the relationship between the landscape surrounding these habitats and the probability of nest predation is uncertain. Moreover, factors associated with reproductive success could be a potentially powerful indicator of ecological condition in wetland habitats. We investigated the influence of landscape pattern on nest success by monitoring 366 red-winged blackbird nests in 11 coastal wetlands along the south shore of Lake Superior. Of the 366 nests, 39% were successful, 56% failed, and 5% were abandoned or lacked sufficient evidence to determine nest fate. Nest predation accounted for over 93% of total failures. Predation rates ranged from 31% to 97% among the 11 wetland sites. We modeled nest predation using multi-model logistic regression analysis and the Akaike information criterion to identify and parameterize influential variables derived from the nest site, wetland, and landscape surrounding each wetland. Our results indicated that landscape variables comprised over 50% of model prediction weight in 15 of the 17 models. Nest failure was highest at sites within an urban/residential landscape matrix. Reproductive success could be a good indicator of the ecological health of Great Lakes wetlands.
Submergent aquatic vegetation (SAV) is a powerful indicator of environmental conditions in both m... more Submergent aquatic vegetation (SAV) is a powerful indicator of environmental conditions in both marine and fresh water ecosystems. Quickbird imagery was used to map SAV at three sites across the Great Lakes. Unsupervised classifications were performed at each site using summer Quickbird sensor data. At one site, a multi-temporal classification approach was added, combining visible red difference (May-August) with August red and green visible band data. Multi-temporal SAV classification was superior to single-date results at this site. Muck bottom was not seriously confused with SAV, which was unexpected. Multi-temporal classification results showed less confusion between deep water and SAV, although spectral variability due to sub-surface sandbar structure was a source of error in both single-and multi-date classifications. Nevertheless, some of the confounding effects of water column on SAV classification appear to have been mitigated using this multi-temporal approach. Future efforts would be well served by incorporating detailed, continuous, bathymetry data in the classification process. Quickbird sensor data are very useful for classifying SAV under US Great Lakes conditions. However, regional classification efforts using these data may be impractical at this time, as high cost, rigid tasking parameters and unpredictable water conditions limit availability of suitable imagery.
To evaluate the relative effect of autecologic factors, site-specific factors, disturbance charac... more To evaluate the relative effect of autecologic factors, site-specific factors, disturbance characteristics, and community structure on the recovery of temperate-stream fish communities, we reviewed case histories for 49 sites and recorded data on 411 recovery end points. Most data were derived from studies of low-gradient third-or fourth-order temperate streams located in forested or agricultural watersheds. Species composition, species richness, and total density all recovered within one year for over 70% ot systems studied. Lotic fish communities were not resilient to press disturbances (e.g., mining, logging, channelization) in the absence of mitigation efforts (recovery time >5 to >52 yr) and in these cases recovery was limited by habitat quality. Following pulse disturbances, autecological factors, site-specific factors, and disturbance-specific factors all affected rates of recovery. Centrarchids and minnows were most resilient to disturbance, while salmonid populations were least resilient of all families considered. Species within rock-substrate/nest-spawning guilds required significantly longer time periods to either recolonize or reestablish predisturbance population densities than did species within other reproductive guilds. Recovery was enhanced by the presence of refugia but was delayed by barriers to migration, especially when source populations for recolonization were relatively distant. Median population recovery times for systems in which disturbances occurred during or immediately prior to spawning were significantly less than median recovery times for systems in which disturbances occurred immediately after spawning. There was little evidence for the influence of biotic interactions on recovery rates. While studies of the effect of natural and anthropogenie disturbances on fish populations are common, relatively few studies examine the recovery of fish populations and communities (Niemi and others 1990). Data on recovery rates of aquatic communities are necessary not only for establishing exceedance criteria for water quality standards (Platkin 1988), but also for testing current ecological theory (Resh and others 1988, Yount and Niemi 1990). Theories concerning the role of biotic versus abiotic control of fish communities (Schoener 1987), the role of succession in streams (Fisher 1983), island biogeugraphy theory (Minshall and others 1983), life history strategies, zoogeographical constraints, the effects of euvironmenud wiriability, and the effect of food web complexity on the stability of fish communities (Horwi~ 1978, DeAngelis and others 1989, Poff and Ward 1990, Reice and others 1990) are all relevant to the study of recovery processes. In this study, we review case ifistories containing data orl iish recovery rates in temperate streams and explore the
A better understanding of relationships between human activities and water chemistry is needed to... more A better understanding of relationships between human activities and water chemistry is needed to identify and manage sources of anthropogenic stress in Great Lakes coastal wetlands. The objective of the study described in this article was to characterize relationships between water chemistry and multiple classes of human activity (agriculture, population and development, point source pollution, and atmospheric deposition). We also evaluated the influence of geomorphology and biogeographic factors on stressor-water quality relationships. We collected water chemistry data from 98 coastal wetlands distributed along the United States shoreline of the Laurentian Great Lakes and GIS-based stressor data from the associated drainage basin to examine stressor-water quality relationships. The sampling captured broad ranges (1.5-2 orders of magnitude) in total phosphorus (TP), total nitrogen (TN), dissolved inorganic nitrogen (DIN), total suspended solids (TSS), chlorophyll a (Chl a), and chloride; concentrations were strongly correlated with stressor metrics. Hierarchical partitioning and all-subsets regression analyses were used to evaluate the independent influence of different stressor classes on water quality and to identify best predictive models. Results showed that all categories of stress influenced water quality and that the relative influence of different classes of disturbance varied among water quality parameters. Chloride exhibited the strongest relationships with stressors followed in order by TN, Chl a, TP, TSS, and DIN. In general, coarse scale classification of wetlands by morphology (three wetland classes: riverine, protected, open coastal) and biogeography (two ecoprovinces: Eastern Broadleaf Forest [EBF] and Laurentian Mixed Forest [LMF]) did not improve predictive models. This study provides strong evidence of the link between water chemistry and human stress in Great Lakes coastal wetlands and can be used to inform management efforts to improve water quality in Great Lakes coastal ecosystems.
Ecological boundaries are critical landscape regions of transition between adjacent ecological sy... more Ecological boundaries are critical landscape regions of transition between adjacent ecological systems. While environmental controls of boundaries may operate in a scale-dependent manner, multiple-scale comparisons of vegetationÁenvironment relationships have been characterized for few boundary systems. We used approximately 250 000 point records on the occurrence of woody versus grassland vegetation in conjunction with climatic, topographical, and soils data to evaluate scale effects and spatial heterogeneity in a 650-km section of the historic prairieÁforest biome boundary of Minnesota, USA. We chose this as a model system because of the availability of historical vegetation data, a considerable spatial extent, a sharp ecological transition, and the ability to avoid confounding from more recent anthropogenic land use change. We developed modeling techniques using hierarchical variance partitioning in a spatially-structured format that allowed us to simultaneously evaluate vegetationÁenvironment relationships across two-dimensional space (i.e. the prairie-forest boundary) and across spatial scales (i.e. varying extents). Soils variables displayed the least spatial autocorrelation at shortest lag distances and tended to be the least important predictors of woody vegetation at all spatial extents. Topographical variables displayed greater spatial heterogeneity in regions dominated by forest compared with prairie and were more important at fine-intermediate spatial scales, highlighting their likely control on fire regimes. An integrated climatic variable (precipitation minus potential evapotranspiration) displayed a trend of increasing spatial variance across the study region and was unambiguously the strongest biome boundary control, although its joint influence with fire was difficult to characterize. Spatially heterogeneous vegetationÁenvironment relationships were observed at all scales, especially at finer scales. Our results suggest that the importance of environmental controls changes smoothly rather than discretely across scales and demonstrate the need to account for spatial non-stationarity and scale to predict and understand vegetation distribution across ecological boundaries.
Artificial ground nests were placed in medium-age or older forests adjoining (a) stands of regene... more Artificial ground nests were placed in medium-age or older forests adjoining (a) stands of regenerating forest (vegetation < 2 m high) where ' hard' edges were created, and (b) stands of young forest (vegetation 2-8 m high) where ' soft' edges were created. Nests were placed at three distances from the forest edge (0 m, SO m, and 100 m). Two Northern Bobwhite Quail (Colinus ~ir;~inianus) eggs were placed in each nest and monitored after 7 and 14 days of exposure between late May and mid-July, 1994. Overall nest predation was 72% after 7 days and 85% after 14 days of exposure. Predation near soft edges was significantly higher than near hard edges after both 7 and 14 days of exposure. Predation near the edges was significantly higher than away from the edges after both 7 and 14 days of exposure. Two motion-sensitive cameras were used to record the identity of predator species. Cameras documented 28 predation events during 1,728 hours of operation, caused by eight species of mammals. The predators included, in order of decreasing predation: fisher (Murtes pennanti), Eastern chipmunk (Tumias striatus), red-backed vole (Clethrionomys gapperi), red squirrel (Tamiasciurus hudsonicus), deer mouse (Peromyscus maniculutus), black bear (~rsus americanus), gray squirrel (Sciurus carolinensis), and striped skunk (Menhitis menhitis). The relationshiv between edges, predator assemblages,^and nest succe& is complex; &ore studies at the' landscape level are required to better understand the effects of these factors on avian population dynamics.
Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were ... more Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were compared to invertebrate availability as measured by aerial tow nets. The majority of the biomass in the nestlings' diet was adult insects with larval stages of aquatic origin, while absolute numbers of insects of both aquatic and terrestrial origin were similar. Orders of invertebrates in the diet and available were similar in number but not in biomass. Diet showed little variation by time of day, date of sampling or the age of Manuscript
Influence of call broadcast timing within point counts and survey duration on detection probabili... more Influence of call broadcast timing within point counts and survey duration on detection probability of marsh breeding birds.
Human-induced effects on lowland conifer forests in hemiboreal regions are increasing because of ... more Human-induced effects on lowland conifer forests in hemiboreal regions are increasing because of expanded use of these northern ecosystems for raw materials, energy, and minerals as well as the potential effects of climatic changes. These forests support many breeding bird species across the Holarctic and allow the persistence of several boreal bird species in hemiboreal and even temperate regions. These bird species are of particular conservation concern as shifting patterns northward in forest composition caused by climate change will likely affect their populations. However, effective management and conservation options are limited because the specifics of these species' breeding habitats are not well understood. We modeled and mapped habitat suitability for 11 species of boreal birds that breed in the lowland conifer forests of the Agassiz Lowlands Ecological Subsection in northern Minnesota and are likely to have reduced breeding habitat in the future: Spruce Grouse (Falcipennis canadensis), Black-backed Woodpecker (Picoides arcticus), Olivesided Flycatcher (Contopus cooperi), Yellow-bellied Flycatcher (Empidonax flaviventris), Boreal Chickadee (Poecile hudsonicus), Goldencrowned Kinglet (Regulus satrapa), Ruby-crowned Kinglet (Regulus calendula), Swainson's Thrush (Catharus ustulatus), Connecticut Warbler (Oporornis agilis), Palm Warbler (Setophaga palmarum), and Dark-eyed Junco (Junco hyemalis). Sets of 7 to 16 potential environmental covariates, including both stand-level and landscape attributes, were used to develop individual species models. Within this lowland conifer-dominated ecosystem, we found significant selection for specific forest and landscape characteristics by all but one of these species, with the best models including between one and nine variables. Habitat suitability maps were developed from these models and predictions tested with an independent dataset. Model performance depended on species, correctly predicting 56-96% of test data. We present a map combining suitability scores for five species of conservation concern that has been used for conservation planning and management opportunities across a broad, lowland forest landscape. We recommend managers utilize the detailed model development and validation framework to address local and regional conservation issues.
Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were ... more Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were compared to invertebrate availability as measured by aerial tow nets. The majority of the biomass in the nestlings' diet was adult insects with larval stages of aquatic origin, while absolute numbers of insects of both aquatic and terrestrial origin were similar. Orders of invertebrates in the diet and available were similar in number but not in biomass. Diet showed little variation by time of day, date of sampling or the age of Manuscript
We established bird monitoring programs in two regions of Minnesota: the Chippewa National Forest... more We established bird monitoring programs in two regions of Minnesota: the Chippewa National Forest and the Superior National Forest. The experimental design defined forest cover types as strata in which samples of forest stands were randomly selected. Subsamples (3 point counts) were placed in each stand to maximize field effort and to assess within-stand and between-stand variation for a variety of bird parameters. Data gathered in 1991 were used to evaluate several assumptions that were made in the experimental design and showed that variance of most bird parameters among strata were similar. This data indicated that a proportional stratified sample by forest cover type was reasonable. We also found that two subsamples per stand would be optimum when a variety of strata types and bird variables were considered. Analyses based on 120 stands in the Chippewa National Forest and 150 stands in the Superior National Forest indicated that a two-tailed t-test could detect a 25 percent change in bird numbers for common species. For most other species, we could detect less than a 50 percent annual change. Monitoring programs within regions should be habitat specific so that changes in bird numbers can be related to: (1) habitat changes that have occurred in the region; (2) natural fluctuations in bird numbers; or (3) other factors.
The Canada Warbler (Cardellina canadensis) is a species of high conservation importance because o... more The Canada Warbler (Cardellina canadensis) is a species of high conservation importance because of its low overall density and long-term widespread population declines on the breeding grounds. Results of previous research on the species suggest that its breeding habitat preferences vary across its range. However, the underlying processes associated with habitat use are unknown. Using a 20 yr dataset, we developed occupancy models for Canada Warblers to determine the influence of habitat characteristics (e.g., understory vegetation, canopy cover), landscape context (e.g., edge, forest patch size), and species co-occurrence on occupancy, colonization, and local extinction parameters. Our results show that multiple habitats are used by Canada Warblers on the breeding grounds; common variables associated with large-scale, long-term occupancy dynamics are forest age, landscape composition at the 100 m and 500 m scales, and mean patch size. Overall, Canada Warblers were nearly twice as persistent in mature forest stands (.80 yr) and large, mixed forest stands. Further, models indicated that species co-occurrence was an important predictor of Canada Warbler occupancy in some cover types. The results of this study increase our understanding of population processes over large, dynamic landscapes and provide essential conservation information to improve habitat and landscape management for the Canada Warbler.
Continental-scale monitoring programs with standardized survey protocols play an important role i... more Continental-scale monitoring programs with standardized survey protocols play an important role in conservation science by identifying species in decline and prioritizing conservation action. However, rare, inaccessible, or spatially fragmented communities may be underrepresented in continental-scale surveys. Data on these communities often come from decentralized, local monitoring efforts that differ in their goals and survey protocols. We combine 16 point count datasets, controlling for differences in protocol and detection probabilities to estimate regional trends for 14 spruce-fir forest bird species across Northeastern and Midwestern United States, a vulnerable community threatened by numerous anthropogenic stressors and widely considered a priority for conservation. Our analyses indicated that four species considered as ecological indicators for this community, Bicknell's Thrush (Catharus bicknelli), Magnolia Warbler (Setophaga magnolia), Blackpoll Warbler (Setophaga striata) and Yellow-bellied Flycatcher (Empidonax flaviventris), each exhibited significant declines. Olive-sided Flycatcher (Contopus cooperi), a species of concern in parts of its range, and two additional species for which no previous concern existed, the Evening Grosbeak (Coccothruastes vespertinus) and the Gray Jay (Perisoreus canadensis), each also showed significant overall declines. Five out of nine species with sufficient data for analyses from Northeastern and Midwestern surveys showed significant differences in trends between these regions. Spruce-fir obligate species were more likely to decline significantly than species that use spruce-fir in addition to other habitat types. These results demonstrate the value of combining disparate data sources for analyzing regional patterns of population trends to confirm and extend conservation concern for some species and identify others for which additional attention may be needed.
Establishing whether conditions are suitable for reproduction would help determine if immigration... more Establishing whether conditions are suitable for reproduction would help determine if immigration is necessary for Canada lynx (Lynx canadensis) to persist at the southern edge of the species range. We located den sites and monitored reproduction of radiocollared lynx in Minnesota from 2004 to 2006. Movement rates of denning females measured with Global Positioning System collars were similar to movement rates of lynx elsewhere. Female lynx with kittens used different habitat types in predenning, denning, and postdenning periods. Landscape composition at the scale of the foraging radius around a den site contained more lowland conifer, upland conifer, and regenerating forest than did home ranges or the area used by radiocollared lynx in Minnesota, USA. We used the spatial distribution of cover-type composition around known den sites to predict and map potential denning habitat in northeastern Minnesota. Techniques for identifying the spatial distribution of suitable denning habitat provide a biological basis for management actions that could enhance recovery of Canada lynx populations in the southern part of the species range.
Questions: Two alternative mechanisms of abrupt vegetation change across ecological boundaries ha... more Questions: Two alternative mechanisms of abrupt vegetation change across ecological boundaries have been proposed: (1) concomitantly abrupt gradients in physical environmental variables and vegetation across the boundary, and (2) gradual environmental gradients that vegetation responds to in a non-linear or threshold manner. Here, we evaluate spatial patterns of climate and vegetation across a grassland-forest biome boundary to examine evidence in favour of either of these alternatives. Location: Minnesota, USA. Methods: Vegetation data represented the presence of prairie vs. forest vegetation in Minnesota from 1847 to 1908, generally prior to European settlement of the region, while the climatic variables represented an index of long-term average moisture availability (precipitation minus potential evapotranspiration (P-PET). Using linear and sigmoidal regression models, we evaluated spatial patterns of change in vegetation, climate and vegetation-climate relationships across 22 transects (170-400 km) oriented perpendicular to the biome boundary. We also evaluated boundary characteristics in light of dominant topographical controls and position along the boundary. Results: Vegetation followed a sigmoidal pattern of change across the boundary, with mean boundary width of ca. 100 km. The P-PET increased by ca. 100 mm across the boundary following a comparatively smooth pattern of change. Climate-vegetation relationships were clearly non-linear across the boundary, indicating these variables did not change in a common spatial pattern. Regional topographical controls modified relationships between vegetation and climate along the length of the boundary. Conclusions: Our results document strong non-linear relationships between the presence of forest vegetation and its dominant climate control across a grassland-forest biome boundary. An average change of ca. 100 mm in P-PET moving across the boundary is about 40% of the long-term mean annual range of this variable, suggesting that modest changes to P-PET may potentially cause substantial shifts in the location of the prairie-forest boundary.
Each autumn, tens of thousands of raptors pass over Hawk Ridge in Duluth, Minnesota, on their sou... more Each autumn, tens of thousands of raptors pass over Hawk Ridge in Duluth, Minnesota, on their southbound migration, but migratory pathways leading to Hawk Ridge are unknown. To address this issue, we counted migrating raptors between mid-August and mid-November 2008 from 24 observation points along eight transects perpendicular to the shoreline between Duluth and the Minnesota-Canadian border. Our goals were to determine migratory pathways over a large area (.2000 km 2) and identify how these movements were affected by weather, time of day, season, and characteristics of the landscape. A total of 4303 raptors of 14 different species were counted during the 2008 migration season. Exploratory analyses suggested that migratory raptors concentrated near the northern shoreline of Lake Superior, particularly during midday when winds are westerly. Average migration height differed between soaring raptors (buteos and eagles) and accipiters, with .40% of soaring raptors observed higher than 100 m above the tree canopy and $30% of accipiters observed lower than 100 m above the tree canopy. Mixed models analysis identified the significant factors (P , 0.05) associated with total raptor migration: wind direction, time of day, temperature, and antecedent wind (number of days in which the wind did not have a westerly component prior to the observation days; R 2 5 0.23). Significant factors associated with soaring-raptor migration included wind direction, time of day, temperature, and seasonal interval (e.g., early or late in the migration season; R 2 5 0.17) and those associated with accipiter migration included time of day, temperature, antecedent wind, wind direction, and seasonal interval (R 2 5 0.29). With the increasing popularity of wind power development, information is needed regarding avian migratory pathways to avoid bird-turbine conflicts. The methodology and design of this study provided a means to quantify the magnitude, timing, pathways, and weather conditions associated with raptor migration over a large landscape.
Space use and movements of Canada lynx (Lynx canadensis) are difficult to study with very-high-fr... more Space use and movements of Canada lynx (Lynx canadensis) are difficult to study with very-high-frequency radiocollars. We deployed global positioning system (GPS) collars on 11 lynx in Minnesota to study their seasonal space-use patterns. We estimated home ranges with minimum-convex-polygon and fixed-kernel methods and estimated core areas with area/probability curves. Fixed-kernel home ranges of males (range ¼ 29-522 km 2) were significantly larger than those of females (range ¼ 5-95 km 2) annually and during the denning season. Some male lynx increased movements during March, the month most influenced by breeding activity. Lynx core areas were predicted by the 60% fixed-kernel isopleth in most seasons. The mean core-area size of males (range ¼ 6-190 km 2) was significantly larger than that of females (range ¼ 1-19 km 2) annually and during denning. Most female lynx were reproductive animals with reduced movements, whereas males often ranged widely between Minnesota and Ontario. Sensitivity analyses examining the effect of location frequency on homerange size suggest that the home-range sizes of breeding females are less sensitive to sample size than those of males. Longer periods between locations decreased home-range and core-area overlap relative to the home range estimated from daily locations. GPS collars improve our understanding of space use and movements by lynx by increasing the spatial extent and temporal frequency of monitoring and allowing home ranges to be estimated over short periods that are relevant to life-history characteristics.
Nest predation has been identified as the primary mechanism contributing to reduction of reproduc... more Nest predation has been identified as the primary mechanism contributing to reduction of reproductive success for the marsh-breeding red-winged blackbird (Agelaius phoeniceus). Differences in rates of nest predation have been linked to nest site characteristics within a wetland, primarily water depth. However, the relationship between the landscape surrounding these habitats and the probability of nest predation is uncertain. Moreover, factors associated with reproductive success could be a potentially powerful indicator of ecological condition in wetland habitats. We investigated the influence of landscape pattern on nest success by monitoring 366 red-winged blackbird nests in 11 coastal wetlands along the south shore of Lake Superior. Of the 366 nests, 39% were successful, 56% failed, and 5% were abandoned or lacked sufficient evidence to determine nest fate. Nest predation accounted for over 93% of total failures. Predation rates ranged from 31% to 97% among the 11 wetland sites. We modeled nest predation using multi-model logistic regression analysis and the Akaike information criterion to identify and parameterize influential variables derived from the nest site, wetland, and landscape surrounding each wetland. Our results indicated that landscape variables comprised over 50% of model prediction weight in 15 of the 17 models. Nest failure was highest at sites within an urban/residential landscape matrix. Reproductive success could be a good indicator of the ecological health of Great Lakes wetlands.
Submergent aquatic vegetation (SAV) is a powerful indicator of environmental conditions in both m... more Submergent aquatic vegetation (SAV) is a powerful indicator of environmental conditions in both marine and fresh water ecosystems. Quickbird imagery was used to map SAV at three sites across the Great Lakes. Unsupervised classifications were performed at each site using summer Quickbird sensor data. At one site, a multi-temporal classification approach was added, combining visible red difference (May-August) with August red and green visible band data. Multi-temporal SAV classification was superior to single-date results at this site. Muck bottom was not seriously confused with SAV, which was unexpected. Multi-temporal classification results showed less confusion between deep water and SAV, although spectral variability due to sub-surface sandbar structure was a source of error in both single-and multi-date classifications. Nevertheless, some of the confounding effects of water column on SAV classification appear to have been mitigated using this multi-temporal approach. Future efforts would be well served by incorporating detailed, continuous, bathymetry data in the classification process. Quickbird sensor data are very useful for classifying SAV under US Great Lakes conditions. However, regional classification efforts using these data may be impractical at this time, as high cost, rigid tasking parameters and unpredictable water conditions limit availability of suitable imagery.
To evaluate the relative effect of autecologic factors, site-specific factors, disturbance charac... more To evaluate the relative effect of autecologic factors, site-specific factors, disturbance characteristics, and community structure on the recovery of temperate-stream fish communities, we reviewed case histories for 49 sites and recorded data on 411 recovery end points. Most data were derived from studies of low-gradient third-or fourth-order temperate streams located in forested or agricultural watersheds. Species composition, species richness, and total density all recovered within one year for over 70% ot systems studied. Lotic fish communities were not resilient to press disturbances (e.g., mining, logging, channelization) in the absence of mitigation efforts (recovery time >5 to >52 yr) and in these cases recovery was limited by habitat quality. Following pulse disturbances, autecological factors, site-specific factors, and disturbance-specific factors all affected rates of recovery. Centrarchids and minnows were most resilient to disturbance, while salmonid populations were least resilient of all families considered. Species within rock-substrate/nest-spawning guilds required significantly longer time periods to either recolonize or reestablish predisturbance population densities than did species within other reproductive guilds. Recovery was enhanced by the presence of refugia but was delayed by barriers to migration, especially when source populations for recolonization were relatively distant. Median population recovery times for systems in which disturbances occurred during or immediately prior to spawning were significantly less than median recovery times for systems in which disturbances occurred immediately after spawning. There was little evidence for the influence of biotic interactions on recovery rates. While studies of the effect of natural and anthropogenie disturbances on fish populations are common, relatively few studies examine the recovery of fish populations and communities (Niemi and others 1990). Data on recovery rates of aquatic communities are necessary not only for establishing exceedance criteria for water quality standards (Platkin 1988), but also for testing current ecological theory (Resh and others 1988, Yount and Niemi 1990). Theories concerning the role of biotic versus abiotic control of fish communities (Schoener 1987), the role of succession in streams (Fisher 1983), island biogeugraphy theory (Minshall and others 1983), life history strategies, zoogeographical constraints, the effects of euvironmenud wiriability, and the effect of food web complexity on the stability of fish communities (Horwi~ 1978, DeAngelis and others 1989, Poff and Ward 1990, Reice and others 1990) are all relevant to the study of recovery processes. In this study, we review case ifistories containing data orl iish recovery rates in temperate streams and explore the
A better understanding of relationships between human activities and water chemistry is needed to... more A better understanding of relationships between human activities and water chemistry is needed to identify and manage sources of anthropogenic stress in Great Lakes coastal wetlands. The objective of the study described in this article was to characterize relationships between water chemistry and multiple classes of human activity (agriculture, population and development, point source pollution, and atmospheric deposition). We also evaluated the influence of geomorphology and biogeographic factors on stressor-water quality relationships. We collected water chemistry data from 98 coastal wetlands distributed along the United States shoreline of the Laurentian Great Lakes and GIS-based stressor data from the associated drainage basin to examine stressor-water quality relationships. The sampling captured broad ranges (1.5-2 orders of magnitude) in total phosphorus (TP), total nitrogen (TN), dissolved inorganic nitrogen (DIN), total suspended solids (TSS), chlorophyll a (Chl a), and chloride; concentrations were strongly correlated with stressor metrics. Hierarchical partitioning and all-subsets regression analyses were used to evaluate the independent influence of different stressor classes on water quality and to identify best predictive models. Results showed that all categories of stress influenced water quality and that the relative influence of different classes of disturbance varied among water quality parameters. Chloride exhibited the strongest relationships with stressors followed in order by TN, Chl a, TP, TSS, and DIN. In general, coarse scale classification of wetlands by morphology (three wetland classes: riverine, protected, open coastal) and biogeography (two ecoprovinces: Eastern Broadleaf Forest [EBF] and Laurentian Mixed Forest [LMF]) did not improve predictive models. This study provides strong evidence of the link between water chemistry and human stress in Great Lakes coastal wetlands and can be used to inform management efforts to improve water quality in Great Lakes coastal ecosystems.
Ecological boundaries are critical landscape regions of transition between adjacent ecological sy... more Ecological boundaries are critical landscape regions of transition between adjacent ecological systems. While environmental controls of boundaries may operate in a scale-dependent manner, multiple-scale comparisons of vegetationÁenvironment relationships have been characterized for few boundary systems. We used approximately 250 000 point records on the occurrence of woody versus grassland vegetation in conjunction with climatic, topographical, and soils data to evaluate scale effects and spatial heterogeneity in a 650-km section of the historic prairieÁforest biome boundary of Minnesota, USA. We chose this as a model system because of the availability of historical vegetation data, a considerable spatial extent, a sharp ecological transition, and the ability to avoid confounding from more recent anthropogenic land use change. We developed modeling techniques using hierarchical variance partitioning in a spatially-structured format that allowed us to simultaneously evaluate vegetationÁenvironment relationships across two-dimensional space (i.e. the prairie-forest boundary) and across spatial scales (i.e. varying extents). Soils variables displayed the least spatial autocorrelation at shortest lag distances and tended to be the least important predictors of woody vegetation at all spatial extents. Topographical variables displayed greater spatial heterogeneity in regions dominated by forest compared with prairie and were more important at fine-intermediate spatial scales, highlighting their likely control on fire regimes. An integrated climatic variable (precipitation minus potential evapotranspiration) displayed a trend of increasing spatial variance across the study region and was unambiguously the strongest biome boundary control, although its joint influence with fire was difficult to characterize. Spatially heterogeneous vegetationÁenvironment relationships were observed at all scales, especially at finer scales. Our results suggest that the importance of environmental controls changes smoothly rather than discretely across scales and demonstrate the need to account for spatial non-stationarity and scale to predict and understand vegetation distribution across ecological boundaries.
Artificial ground nests were placed in medium-age or older forests adjoining (a) stands of regene... more Artificial ground nests were placed in medium-age or older forests adjoining (a) stands of regenerating forest (vegetation < 2 m high) where ' hard' edges were created, and (b) stands of young forest (vegetation 2-8 m high) where ' soft' edges were created. Nests were placed at three distances from the forest edge (0 m, SO m, and 100 m). Two Northern Bobwhite Quail (Colinus ~ir;~inianus) eggs were placed in each nest and monitored after 7 and 14 days of exposure between late May and mid-July, 1994. Overall nest predation was 72% after 7 days and 85% after 14 days of exposure. Predation near soft edges was significantly higher than near hard edges after both 7 and 14 days of exposure. Predation near the edges was significantly higher than away from the edges after both 7 and 14 days of exposure. Two motion-sensitive cameras were used to record the identity of predator species. Cameras documented 28 predation events during 1,728 hours of operation, caused by eight species of mammals. The predators included, in order of decreasing predation: fisher (Murtes pennanti), Eastern chipmunk (Tumias striatus), red-backed vole (Clethrionomys gapperi), red squirrel (Tamiasciurus hudsonicus), deer mouse (Peromyscus maniculutus), black bear (~rsus americanus), gray squirrel (Sciurus carolinensis), and striped skunk (Menhitis menhitis). The relationshiv between edges, predator assemblages,^and nest succe& is complex; &ore studies at the' landscape level are required to better understand the effects of these factors on avian population dynamics.
Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were ... more Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were compared to invertebrate availability as measured by aerial tow nets. The majority of the biomass in the nestlings' diet was adult insects with larval stages of aquatic origin, while absolute numbers of insects of both aquatic and terrestrial origin were similar. Orders of invertebrates in the diet and available were similar in number but not in biomass. Diet showed little variation by time of day, date of sampling or the age of Manuscript
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