Differential migration by age and sex in central European Ospreys Pandion haliaetus

Abstract

Differential migration reflects various constraints and selective forces on different individuals in a population, and has been explained by several hypotheses. Most previous studies about differential migration focused on only one aspect (e.g. spring timing, autumn timing or wintering area), which could not give a full picture of differential migration of the study population and carry out an overall investigation into the hypotheses. In this study, we analyse the migration patterns of European Ospreys Pandion haliaetus ringed in Germany based on the ring recovery database between 1980 and 2008. The migration routes of the study population form a broad front between south and southwest of the ringing area, and the wintering sites are in West Africa south of the Sahara and around the western Mediterranean. We demonstrate differential migration of the population in both spring and autumn timings as well as in the use of wintering grounds. Adult (third year and older) males return earliest to the breeding area in spring, followed by adult females and then twoyear-old birds. In autumn, the adult females leave the breeding area earlier than adult males, while the migration of first-year Ospreys takes place over a wide time-span. Adult males were discovered mainly around the western Mediterranean in winter, closer to the ringing area than adult females and younger birds. We suggest that the selection for prior access to breeding resources on males shapes the patterns of differential migration in Ospreys.

Differential wintering area selection in Eurasian Marsh Harrier (Circus aeruginosus): a ringing recoveries analysis

“…This fits with the results of visual observations carried out in the Mediterranean basin, both at migration bottlenecks and at wintering sites, that showed a stronger tendency for adult male Eurasian Marsh Harriers to migrate over longer distances than adult females, because an imbalance towards males has been observed during migration en route and from Africa, with the opposite trend at wintering sites in Italy (Agostini & Logozzo 2000, Agostini et al 2003, Panuccio et al 2005a, 2005b, 2012, Agostini & Panuccio 2010. It has been suggested that this latitudinal segregation of the sexes is promoted by sexual dimorphism, because females, being larger, are more adept than smaller males in taking larger prey items and coping with colder temperature, on the basis of the Bergman's rule (Cristol et al 1999, Panuccio et al 2005a.…”

“…It has been suggested that this latitudinal segregation of the sexes is promoted by sexual dimorphism, because females, being larger, are more adept than smaller males in taking larger prey items and coping with colder temperature, on the basis of the Bergman's rule (Cristol et al 1999, Panuccio et al 2005a. As in other studies based on ringing recovery data, it is likely that the proportion of the population wintering in Africa is greater than that shown by our data set, because ring monitoring in Europe is more widespread compared to Africa (Bai & Schmidt 2012 When considering individuals wintering south of Sahara desert, juveniles were distributed significantly more west during the winter than adults, even when accounting for the latitude of the breeding site. One possible explanation of this might be a differential response to the prevailing winds.…”

“…Within a given population, migration timing and/or distance can vary according to age-and/or sexclasses (differential migration; Cristol et al 1999, Bai & Schmidt 2012. Among different populations, geographical location of breeding areas can be another source of variation.…”

The demography of a newly establishedOspreyPandion haliaetuspopulation inFrance

“…Breeding individuals defend their nest‐site (at a distance of 20–50 m, Jamieson & Seymour ), but not feeding territories (Poole ). In continental France, breeding individuals migrate mainly to West Africa to spend the winter months (Wahl ,b), although some first‐year birds stay in the Iberian Peninsula on their first migration (Bai & Schmidt ). Males and females arrive at their breeding grounds in February–March (Thiollay & Wahl ).…”

Cold tolerance, and not earlier arrival on breeding grounds, explains why males winter further north in an Arctic‐breeding songbird

“…Variation in the distribution of the sexes during the nonbreeding period over broad geographic ranges or locally by habitat is a widespread phenomenon among migratory taxa (Stewart 1997, Marra 2001, Phillips et al 2004). These patterns are particularly evident in species also exhibiting sexual size dimorphism or differences in migration schedules (Myers 1981, Bai andSchmidt 2012). For birds wintering in temperate regions, the 'body size hypothesis' predicts that the larger sex (often males) will occupy colder non-breeding sites relative to the smaller sex, owing to a thermoregulatory advantage in cold-tolerance Nolan Jr 1976, Cristol et al 1999).…”