Doi: https://doi.org/10.13157/arla.70.2.2023.ra5
Authors: Mª Luisa MARCOS PACHECO, Giacomo TAVECCHIA, José Manuel IGUAL, Carlos ALONSO-ÁLVAREZ, Juan ARIZAGA, Aitor GALARZA, Daniel ORO and Alejandro MARTÍNEZ-ABRAÍN
E-mail: a.abrain@udc.es
Published: Volume 70.2, July 2023. Pages 225-240.
Language: English
Keywords: adaptation, allometry, biometry, migration, oceanographic conditions and sexual dimorphism
Summary:
Variability in morphology and body size between populations of the same species is common and can be influenced by environmental conditions or differential migratory strategies. We focused on analysing body size differences between Yellow-legged gulls Larus michahellis from Mediterranean and Cantabrian-Atlantic Iberian colonies as previous studies have suggested that Cantabrian-Atlantic gulls are smaller than Mediterranean gulls. However, those analyses were based on small sample sizes or did not account for sexual dimorphism. Here we analyse an extensive biometric data set (> 1,500 adult individuals), separating males and females, from nine different sites in each region. Our results reveal a 7% (median) difference both between regions and sexes, for most morphometric variables, with Mediterranean gulls having longer legs (tarsi) and heads (cranium-bill) and thicker bills (bill-depth). This inter-regional difference was even larger for body mass, Mediterranean gulls being 11% (males) and 20% (females) heavier than Cantabrian-Atlantic gulls. In particular, we found that individuals from the Mediterranean populations were allometrically longer-winged than their northern counterparts. We suggest, after discarding other factors, that this wing allometry may be related to the sedentariness of the Cantabrian-Atlantic gulls, compared with the partially migratory strategy of Mediterranean gulls. We also suggest that the larger body size of Mediterranean gulls may help them compete better with resident gulls for food acquisition, once they coincide in the Cantabrian-Atlantic region. Finally, females from both populations were also found to be proportionately longerwinged than males. We hypothesise that this difference could allow smaller females to travel longer distances locally in search of food or to make use of different habitat types, avoiding foraging competition with the larger males.
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