Background: Invasive plants are associated with the decline of native plant richness, but the imp... more Background: Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. Aims: We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C. solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C. solstitialis. Methods: From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m 2 plots in C. solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Results: Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C. solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Conclusions: Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall.
Latitudinal clines in sex ratio during the nonbreeding season occur in some shorebirds of the Sco... more Latitudinal clines in sex ratio during the nonbreeding season occur in some shorebirds of the Scolopacidae. We compared populations of nonbreeding Dunlin (Calidris alpina pacifica) from two latitudes along the Pacific flyway: the Fraser River Delta, British Columbia, and Bolinas Lagoon, California, to determine whether, and to what degree, they exhibited sex ratios consistent with a latitudinal cline. Dunlin are plumage monomorphic, so we used a maximum likelihood model to estimate overall and monthly sex ratios for each population based on culmen length distributions. Sex ratios in the Fraser River Delta were corrected for sex differences in habitat use. Monthly sex ratios were similar at the two sites but varied throughout the winter, likely reflecting differences in seasonal movement patterns between the sexes. Both populations showed an overall bias toward males (Fraser ϭ 61% males, Bolinas ϭ 65% males). Since there is no evidence to support the possibility of a skew toward males in C. a. pacifica as a whole, our data are consistent with some form of latitudinal cline in the sex ratio of C. a. pacifica. However, additional data from the Oregon coast, southern California, and Mexico are required to resolve this question. We also tested the hypothesis that mean body size within each sex is larger at the higher-latitude site (Fraser River Delta), but this did not appear to be the case.
Worldwide, shorebird populations are declining. Our objectives were to examine abundance trends o... more Worldwide, shorebird populations are declining. Our objectives were to examine abundance trends of shorebirds regularly wintering at Tomales Bay, Marin County, California, accounting for the local effects of rainfall, raptors, and the restoration of part of the bay to tidal wetlands. From November 1989 to February 2019, we conducted 177 comprehensive winter shorebird surveys of Tomales Bay; we averaged 5.7 ± 0.9 (mean ± SD) winter surveys per year. In 30 yr, we counted 1,215,821 shorebirds of 31 species. We used generalized linear models and multi-model inference to evaluate trends in shorebird abundance while accounting for local sources of variation. We conducted separate analyses for 14 species seen in at least 20 of the 30 yr of monitoring and for all shorebird species combined. During the study, the abundance of all species combined declined 66% (52% in the North Bay and 81% in the South Bay) with the most rapid decline in the first 10 yr of monitoring. Of 13 species for which ...
Background: Invasive plants are associated with the decline of native plant richness, but the imp... more Background: Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. Aims: We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C. solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C. solstitialis. Methods: From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m 2 plots in C. solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Results: Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C. solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Conclusions: Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall.
Western Sandpipers Calidris mauri are differential migrants on their non-breeding areas, with fem... more Western Sandpipers Calidris mauri are differential migrants on their non-breeding areas, with females wintering farther south. Earlier passage of males in the spring has been explained by sexual differences in winter latitude (male-biased sex ratios at more northerly areas) and onset of migration (males departing earlier). We investigated sex differences during spring migration by capturing and radio-marking Western Sandpipers at two Pacific coast sites, San Francisco Bay, California and Grays Harbor, Washington and at a Great Basin interior wetland, Honey Lake, California. We monitored northward migration of 132 radio-marked birds at a network of 12 major stopover sites and 4 breeding areas. At the banding sites, we observed differences in sex by date and site, with males preceding females. We found sex differences in departure time of radio-marked birds from the banding site. their arrival time at the Copper River Delta, Alaska (our most frequently used stopover site), and in the likelihood that a stopover was used. Our data suggest that by mid to late April, migration timing becomes more compressed and sex differences are less pronounced and harder to detect.
... future directions NILS WARNOCK • & JOHN Y. TAKEKAWA 2 ... Cresswell et al. (in press)... more ... future directions NILS WARNOCK • & JOHN Y. TAKEKAWA 2 ... Cresswell et al. (in press) used a similar system to study the incubation behaviour of Semipalmated Sandpipers, although the PIT tag was epoxied to the outer surface of a leg band. ...
... 131-139 NON-MIGRATORY MOVEMENTS OF DUNLINS ON THEIR CALIFORNIA WINTERING GROUNDS Nils Warnock... more ... 131-139 NON-MIGRATORY MOVEMENTS OF DUNLINS ON THEIR CALIFORNIA WINTERING GROUNDS Nils Warnock.,1 Gary W. Page,2 ... wetlands in providing habitat for wintering shorebirds and lead to a more comprehensive conservation strategy for west coast shorebirds. ...
... Bay. Four l.3-g radio-transmitters (Holohil Systems Ltd., 3387 Stonecrest Rd, Woodlawn, Ontar... more ... Bay. Four l.3-g radio-transmitters (Holohil Systems Ltd., 3387 Stonecrest Rd, Woodlawn, Ontario K0A 3M0, Canada) were glued to the upper backs of Dunlins with cyanoacrylate (Superglue). Additionally ... basis. Bolinas Lagoon In ...
... Tests were two-tailed, significance was set at P - 0.05, and statistical analyses were perfor... more ... Tests were two-tailed, significance was set at P - 0.05, and statistical analyses were performed using STATA (Release 5.0, Stata Press, College Station ... aropes were higher in 1997 than in 1996 at Sum-mer and Abert Lakes but not Goose Lake (Table 2). Lake Abert had highest ...
Background: Invasive plants are associated with the decline of native plant richness, but the imp... more Background: Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. Aims: We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C. solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C. solstitialis. Methods: From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m 2 plots in C. solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Results: Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C. solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Conclusions: Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall.
Latitudinal clines in sex ratio during the nonbreeding season occur in some shorebirds of the Sco... more Latitudinal clines in sex ratio during the nonbreeding season occur in some shorebirds of the Scolopacidae. We compared populations of nonbreeding Dunlin (Calidris alpina pacifica) from two latitudes along the Pacific flyway: the Fraser River Delta, British Columbia, and Bolinas Lagoon, California, to determine whether, and to what degree, they exhibited sex ratios consistent with a latitudinal cline. Dunlin are plumage monomorphic, so we used a maximum likelihood model to estimate overall and monthly sex ratios for each population based on culmen length distributions. Sex ratios in the Fraser River Delta were corrected for sex differences in habitat use. Monthly sex ratios were similar at the two sites but varied throughout the winter, likely reflecting differences in seasonal movement patterns between the sexes. Both populations showed an overall bias toward males (Fraser ϭ 61% males, Bolinas ϭ 65% males). Since there is no evidence to support the possibility of a skew toward males in C. a. pacifica as a whole, our data are consistent with some form of latitudinal cline in the sex ratio of C. a. pacifica. However, additional data from the Oregon coast, southern California, and Mexico are required to resolve this question. We also tested the hypothesis that mean body size within each sex is larger at the higher-latitude site (Fraser River Delta), but this did not appear to be the case.
Worldwide, shorebird populations are declining. Our objectives were to examine abundance trends o... more Worldwide, shorebird populations are declining. Our objectives were to examine abundance trends of shorebirds regularly wintering at Tomales Bay, Marin County, California, accounting for the local effects of rainfall, raptors, and the restoration of part of the bay to tidal wetlands. From November 1989 to February 2019, we conducted 177 comprehensive winter shorebird surveys of Tomales Bay; we averaged 5.7 ± 0.9 (mean ± SD) winter surveys per year. In 30 yr, we counted 1,215,821 shorebirds of 31 species. We used generalized linear models and multi-model inference to evaluate trends in shorebird abundance while accounting for local sources of variation. We conducted separate analyses for 14 species seen in at least 20 of the 30 yr of monitoring and for all shorebird species combined. During the study, the abundance of all species combined declined 66% (52% in the North Bay and 81% in the South Bay) with the most rapid decline in the first 10 yr of monitoring. Of 13 species for which ...
Background: Invasive plants are associated with the decline of native plant richness, but the imp... more Background: Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. Aims: We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C. solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C. solstitialis. Methods: From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m 2 plots in C. solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Results: Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C. solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Conclusions: Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall.
Western Sandpipers Calidris mauri are differential migrants on their non-breeding areas, with fem... more Western Sandpipers Calidris mauri are differential migrants on their non-breeding areas, with females wintering farther south. Earlier passage of males in the spring has been explained by sexual differences in winter latitude (male-biased sex ratios at more northerly areas) and onset of migration (males departing earlier). We investigated sex differences during spring migration by capturing and radio-marking Western Sandpipers at two Pacific coast sites, San Francisco Bay, California and Grays Harbor, Washington and at a Great Basin interior wetland, Honey Lake, California. We monitored northward migration of 132 radio-marked birds at a network of 12 major stopover sites and 4 breeding areas. At the banding sites, we observed differences in sex by date and site, with males preceding females. We found sex differences in departure time of radio-marked birds from the banding site. their arrival time at the Copper River Delta, Alaska (our most frequently used stopover site), and in the likelihood that a stopover was used. Our data suggest that by mid to late April, migration timing becomes more compressed and sex differences are less pronounced and harder to detect.
... future directions NILS WARNOCK • & JOHN Y. TAKEKAWA 2 ... Cresswell et al. (in press)... more ... future directions NILS WARNOCK • & JOHN Y. TAKEKAWA 2 ... Cresswell et al. (in press) used a similar system to study the incubation behaviour of Semipalmated Sandpipers, although the PIT tag was epoxied to the outer surface of a leg band. ...
... 131-139 NON-MIGRATORY MOVEMENTS OF DUNLINS ON THEIR CALIFORNIA WINTERING GROUNDS Nils Warnock... more ... 131-139 NON-MIGRATORY MOVEMENTS OF DUNLINS ON THEIR CALIFORNIA WINTERING GROUNDS Nils Warnock.,1 Gary W. Page,2 ... wetlands in providing habitat for wintering shorebirds and lead to a more comprehensive conservation strategy for west coast shorebirds. ...
... Bay. Four l.3-g radio-transmitters (Holohil Systems Ltd., 3387 Stonecrest Rd, Woodlawn, Ontar... more ... Bay. Four l.3-g radio-transmitters (Holohil Systems Ltd., 3387 Stonecrest Rd, Woodlawn, Ontario K0A 3M0, Canada) were glued to the upper backs of Dunlins with cyanoacrylate (Superglue). Additionally ... basis. Bolinas Lagoon In ...
... Tests were two-tailed, significance was set at P - 0.05, and statistical analyses were perfor... more ... Tests were two-tailed, significance was set at P - 0.05, and statistical analyses were performed using STATA (Release 5.0, Stata Press, College Station ... aropes were higher in 1997 than in 1996 at Sum-mer and Abert Lakes but not Goose Lake (Table 2). Lake Abert had highest ...
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