Proceedings. Biological sciences / The Royal Society, Jan 7, 2004
Population sex ratios in monogamous birds are often male biased. One factor that can affect popul... more Population sex ratios in monogamous birds are often male biased. One factor that can affect population sex ratios is sex-biased predation. However, most estimates of sex-biased predation in birds have focused on species with obvious sexual colour dimorphism or body size dimorphism. Data on sexually monomorphic birds are generally lacking. In the present study, we adopt a PCR-based sexing procedure to help test for sex-biased predation in a wintering population of western sandpipers (Calidris mauri), a shorebird that shows only subtle sexual size dimorphism. Specifically, by comparing the a priori determined sex ratio of live birds wintering at a site in western Mexico to the molecular estimate obtained from depredated birds at this same site, we were able to perform a population-specific test for sex bias in predator-induced mortality. The proportion of females estimated from living (ca. 25%) versus dead (ca. 24%) individuals was in fact not significantly different, indicating that ...
We documented vocalization activity of breeding shorebirds at two sites in northern and western A... more We documented vocalization activity of breeding shorebirds at two sites in northern and western Alaska, on the Colville River Delta and on the Yukon - Kuskokwim Delta. At both sites, number of calling individuals decreased throughout the season. Variation in vocalization activity was significantly higher at the Colville River Delta towards the end of the season, while weather variables affected
Sexual segregation outside the mating season is common in vertebrates, and has been attributed to... more Sexual segregation outside the mating season is common in vertebrates, and has been attributed to sexual differences in predator escape performance in ungulates and fish, but not in birds. Here, we tested the hypothesis that sex-and latitude-specific predator escape performance underlies the differential nonbreeding distribution of western sandpipers (Calidris mauri), a migratory shorebird. Females overwinter further south along the American Pacific coast, creating a latitudinal cline in sex ratio. Escape performance is reduced with increasing body mass, and birds generally carry less fat further south. Western sandpipers with poor escape performance were therefore predicted to prefer southern sites to reduce the risk of mortality posed by predators. Data from four nonbreeding latitudes showed that wing loading, used as an index of escape performance, was overall higher for females, and that it decreased with latitude in both sexes. Within latitudes, wing loading was lower at smaller, and presumably more dangerous, sites. Flight response to a predatory attack was longer in the south. Mortality risk offers a novel and candidate explanation for differential distribution patterns in western sandpipers and possibly other avian migrants.
Spaans 2000. Length of stopover, fuel storage and a sex-bias in the occurrence of two subspecies ... more Spaans 2000. Length of stopover, fuel storage and a sex-bias in the occurrence of two subspecies of Red Knots Calidris c. canutus an d C.c. islandica in the Dutch Wadden Sea --"~during southward migration. Ardea 88(2) : 165-176 . Siberia (C. c. canutus) or north Greenland and north-east Can ada (C. c . islandica), but the details of their co-occurrence have not been described. In 1995-98 numbers of Red Knots in our study area in the western Dutch Wadden Sea usually built up in late July towards maxima of 10 000-20 000 individuals in August and early September. In each of these four years we attached tiny ( 1 .3-1 .8 g) radiotran smi tters to a total of 95 molecularly sexed adults t o -~_ .• f~_: determine the length of stay of different categori es of birds . The 65 females -(68%) predominated the samples, and among the fem ales the majo rity (48 birds) was captured without traces of wing moult . In females, but not in m ales, birds caught in wing moult stayed signific antly longer than non-_ moulting birds. Non-moulting females weighed up to 200 g an d disap-x_ peared within three weeks after being marked . The timing of their disappearance corresponded with observed departures of flocks towards the southwest, and publi shed departure times of canutus . The relationship between length of stay and mass at capture of these early departing nonmoulting fem ales suggests a daily mass gain of about 2 .84 g d-1 . These birds had a mean bill length that was 1 mm (yet signifi c antly) longer th an those of the other femal e categories; a relatively long bill is a well known attribute of ca nutus . The much smaller sample of males with similar mass, moult an d staging time characteristics did not show longer bill lengths and .-~ we are thus unable to unambiguously confirm the presence of canutus males in late July and early August; this bias remains to be functionally J4 explained. Sex ratios were even in birds assignable to islandica . Direc ti e-Noord of the Ministry of Agriculture, Nature migrati on of the Siberian Knots Calidris canutus Conserv ati on and Fisheries, and Rijkswaterstaat grant-canutus : results of a co-operative Wader Study ed us permission to work in the habitats under th eir Group project. Otnis Scand . 18 : 5-16. care. We are very grateful to the m any helpers in the Engelmoer M . & C .S . Roselaar 1998. Geographical field for their enthusiasm and dedication, but wan t to variati on in waders . Kluwer, Dordrecht . van Gil s single out Wi ll em ltenema who put much effort in the J . & T. Piersma 1999 . Day-and night-time movements of radiomarked Red Knots staging in counts an d observ ati ons on Knots at Richel . We th ank the western Wadden Sea in July-August 1995 . Wadthe crews of RV Navicula (Kees van der Star, Johan er Study Group Bull. 89 : 36-44. Tuntelder, Tony van der Vis) and RV Phoca' (Jan van Greenwood J .G. 1986. Geographical variation and tax-Dijk, Dirk Kuiper) for their congenial help, and Annet-onomy of the Dunlin Calidris alpina (L.) . Bu ll . te Greenslade for taking care of the molecular sexing of Brit. Ornith ol . Club 106 : 43-56. the radiomarked birds in the laboratory of Allan J . Bak-Gromadzka J. 1992 . Knots on the Poli sh Baltic coast. er at the Royal Ontario Museum in Toronto, C anada . Wader Study Group Bull. 64, Suppl . : 161-166 . We are also very grateful to Edi th Ries, then of th e Meissner W. 1992 . Knots' autumn migration in the Ins titute for Forestry an d Nature Research (IBN-DLO), western part of the Gulf of Gd ansk, Poland : prelimfor helping us with the aerial surveys to look for radio-ina ry results . Wader Study Group Bu ll . 64, Suppl . : 167-171 . marked birds . Special thanks to Pim Edelaar for his Myers J .P. 1981 a . A test of three hypotheses for latitudihelp during data analyses, and Marcel Klaassen, Hugh nal segrega tion of the sexes in wintering birds . C an. Boyd, Nicola Baccetti and Colin Clark for comments J . Zool . 59: 1527-1534. on th e manuscript. This is NIOZ-publication 3374 . Myers J .P. 1981b . Cross-seasonal interactions in the evolution of san dpiper social systems. Behav. Ecol . Sociobiol. 8 : 195-202.
2003. Cross-seasonal and cross-disciplinary studies of migratory shorebirds. Wader Study Group Bu... more 2003. Cross-seasonal and cross-disciplinary studies of migratory shorebirds. Wader Study Group Bull. 100: 118-121.
Avian species in which males and females migrate to different nonbreeding areas provide candidate... more Avian species in which males and females migrate to different nonbreeding areas provide candidate systems to study ecological factors underlying distribution patterns.
Avian species in which males and females migrate to different nonbreeding areas provide candidate... more Avian species in which males and females migrate to different nonbreeding areas provide candidate systems to study ecological factors underlying distribution patterns.
Proceedings. Biological sciences / The Royal Society, Jan 7, 2004
Population sex ratios in monogamous birds are often male biased. One factor that can affect popul... more Population sex ratios in monogamous birds are often male biased. One factor that can affect population sex ratios is sex-biased predation. However, most estimates of sex-biased predation in birds have focused on species with obvious sexual colour dimorphism or body size dimorphism. Data on sexually monomorphic birds are generally lacking. In the present study, we adopt a PCR-based sexing procedure to help test for sex-biased predation in a wintering population of western sandpipers (Calidris mauri), a shorebird that shows only subtle sexual size dimorphism. Specifically, by comparing the a priori determined sex ratio of live birds wintering at a site in western Mexico to the molecular estimate obtained from depredated birds at this same site, we were able to perform a population-specific test for sex bias in predator-induced mortality. The proportion of females estimated from living (ca. 25%) versus dead (ca. 24%) individuals was in fact not significantly different, indicating that ...
We documented vocalization activity of breeding shorebirds at two sites in northern and western A... more We documented vocalization activity of breeding shorebirds at two sites in northern and western Alaska, on the Colville River Delta and on the Yukon - Kuskokwim Delta. At both sites, number of calling individuals decreased throughout the season. Variation in vocalization activity was significantly higher at the Colville River Delta towards the end of the season, while weather variables affected
Sexual segregation outside the mating season is common in vertebrates, and has been attributed to... more Sexual segregation outside the mating season is common in vertebrates, and has been attributed to sexual differences in predator escape performance in ungulates and fish, but not in birds. Here, we tested the hypothesis that sex-and latitude-specific predator escape performance underlies the differential nonbreeding distribution of western sandpipers (Calidris mauri), a migratory shorebird. Females overwinter further south along the American Pacific coast, creating a latitudinal cline in sex ratio. Escape performance is reduced with increasing body mass, and birds generally carry less fat further south. Western sandpipers with poor escape performance were therefore predicted to prefer southern sites to reduce the risk of mortality posed by predators. Data from four nonbreeding latitudes showed that wing loading, used as an index of escape performance, was overall higher for females, and that it decreased with latitude in both sexes. Within latitudes, wing loading was lower at smaller, and presumably more dangerous, sites. Flight response to a predatory attack was longer in the south. Mortality risk offers a novel and candidate explanation for differential distribution patterns in western sandpipers and possibly other avian migrants.
Spaans 2000. Length of stopover, fuel storage and a sex-bias in the occurrence of two subspecies ... more Spaans 2000. Length of stopover, fuel storage and a sex-bias in the occurrence of two subspecies of Red Knots Calidris c. canutus an d C.c. islandica in the Dutch Wadden Sea --"~during southward migration. Ardea 88(2) : 165-176 . Siberia (C. c. canutus) or north Greenland and north-east Can ada (C. c . islandica), but the details of their co-occurrence have not been described. In 1995-98 numbers of Red Knots in our study area in the western Dutch Wadden Sea usually built up in late July towards maxima of 10 000-20 000 individuals in August and early September. In each of these four years we attached tiny ( 1 .3-1 .8 g) radiotran smi tters to a total of 95 molecularly sexed adults t o -~_ .• f~_: determine the length of stay of different categori es of birds . The 65 females -(68%) predominated the samples, and among the fem ales the majo rity (48 birds) was captured without traces of wing moult . In females, but not in m ales, birds caught in wing moult stayed signific antly longer than non-_ moulting birds. Non-moulting females weighed up to 200 g an d disap-x_ peared within three weeks after being marked . The timing of their disappearance corresponded with observed departures of flocks towards the southwest, and publi shed departure times of canutus . The relationship between length of stay and mass at capture of these early departing nonmoulting fem ales suggests a daily mass gain of about 2 .84 g d-1 . These birds had a mean bill length that was 1 mm (yet signifi c antly) longer th an those of the other femal e categories; a relatively long bill is a well known attribute of ca nutus . The much smaller sample of males with similar mass, moult an d staging time characteristics did not show longer bill lengths and .-~ we are thus unable to unambiguously confirm the presence of canutus males in late July and early August; this bias remains to be functionally J4 explained. Sex ratios were even in birds assignable to islandica . Direc ti e-Noord of the Ministry of Agriculture, Nature migrati on of the Siberian Knots Calidris canutus Conserv ati on and Fisheries, and Rijkswaterstaat grant-canutus : results of a co-operative Wader Study ed us permission to work in the habitats under th eir Group project. Otnis Scand . 18 : 5-16. care. We are very grateful to the m any helpers in the Engelmoer M . & C .S . Roselaar 1998. Geographical field for their enthusiasm and dedication, but wan t to variati on in waders . Kluwer, Dordrecht . van Gil s single out Wi ll em ltenema who put much effort in the J . & T. Piersma 1999 . Day-and night-time movements of radiomarked Red Knots staging in counts an d observ ati ons on Knots at Richel . We th ank the western Wadden Sea in July-August 1995 . Wadthe crews of RV Navicula (Kees van der Star, Johan er Study Group Bull. 89 : 36-44. Tuntelder, Tony van der Vis) and RV Phoca' (Jan van Greenwood J .G. 1986. Geographical variation and tax-Dijk, Dirk Kuiper) for their congenial help, and Annet-onomy of the Dunlin Calidris alpina (L.) . Bu ll . te Greenslade for taking care of the molecular sexing of Brit. Ornith ol . Club 106 : 43-56. the radiomarked birds in the laboratory of Allan J . Bak-Gromadzka J. 1992 . Knots on the Poli sh Baltic coast. er at the Royal Ontario Museum in Toronto, C anada . Wader Study Group Bull. 64, Suppl . : 161-166 . We are also very grateful to Edi th Ries, then of th e Meissner W. 1992 . Knots' autumn migration in the Ins titute for Forestry an d Nature Research (IBN-DLO), western part of the Gulf of Gd ansk, Poland : prelimfor helping us with the aerial surveys to look for radio-ina ry results . Wader Study Group Bu ll . 64, Suppl . : 167-171 . marked birds . Special thanks to Pim Edelaar for his Myers J .P. 1981 a . A test of three hypotheses for latitudihelp during data analyses, and Marcel Klaassen, Hugh nal segrega tion of the sexes in wintering birds . C an. Boyd, Nicola Baccetti and Colin Clark for comments J . Zool . 59: 1527-1534. on th e manuscript. This is NIOZ-publication 3374 . Myers J .P. 1981b . Cross-seasonal interactions in the evolution of san dpiper social systems. Behav. Ecol . Sociobiol. 8 : 195-202.
2003. Cross-seasonal and cross-disciplinary studies of migratory shorebirds. Wader Study Group Bu... more 2003. Cross-seasonal and cross-disciplinary studies of migratory shorebirds. Wader Study Group Bull. 100: 118-121.
Avian species in which males and females migrate to different nonbreeding areas provide candidate... more Avian species in which males and females migrate to different nonbreeding areas provide candidate systems to study ecological factors underlying distribution patterns.
Avian species in which males and females migrate to different nonbreeding areas provide candidate... more Avian species in which males and females migrate to different nonbreeding areas provide candidate systems to study ecological factors underlying distribution patterns.
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