Age-related migration patterns in Larus fuscus spp. |
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Authors: | Paulo A M Marques Ana M Costa Peter Rock Paulo E Jorge |
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Institution: | 1. Centro de Biologia Ambiental, Museu Nacional de História Natural, Universidade de Lisboa, Lisboa, Portugal 2. Departamento de Biodiversidad y Biología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain 3. Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 4. Bristol, UK
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Abstract: | Migration is a critical period in a bird’s life that can affect the fitness of individuals. Intra-population migratory patterns
and the way different sex and/or age classes within a population differ in timing and/or distance of migration are not completely
understood. The present study aims to observe inter- and intra-population migratory patterns in the western population of
Lesser Black-backed Gulls (Larus fuscus spp.), shedding light on age-related differences of temporal patterns of occurrence in the Portuguese coastal areas during
migration and winter. One thousand seven hundred and fifty-four colour ring records were analysed matching a 30-year period
of observations on the Portuguese coast between 1975 and 2005. During migration, the graellsii population represents 90% of the migratory flow of L. fuscus through Portugal with the intermedius accounting for 9% and the fuscus population, being vestigial in this period, accounting for 1%. Nevertheless, interesting significant differences were observed
between the age classes of the three populations during this period, the graellsii population having a large number of first winters (40% of the migratory contingent of this population) followed by immatures
and adults whilst in the intermedius and fuscus populations, the largest age class is the adults. During winter, no inter-population differences were found. When comparing
migration and winter periods, intra-population differences were found in the graellsii and fuscus populations regarding distribution and age classes. These results indicate different migratory routes amongst different populations
suggesting a leapfrog migration in L. fuscus and also a differential age-related migration pattern that might result from first winters migrating further south
in search of a wintering place since adults heavily occupy the closest wintering quarters in their attempt to arrive earlier
at their breeding ground. |
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