Differences in skeletal characters between the disjunct eastern and western populations of ring-billed gulls (Larus delawarensis)

Abstract

Univariate analyses of variance, multivariate analyses of variance (Manova), and discriminant function analyses were performed on measurements of 51 skeletal characters of adult males and females from the disjunct eastern and western populations of the ring-billed gull (Larus delawarensis) in Canada. The analyses established sufficient differences in skeletal characters to permit correct identification of the origin of 34 of 38 males (90%) and 40 of 42 females (95%). The populations are now expanding in range to the extent where new colonies are established in the Lake of the Woods, Ontario region, the historical hiatus between the two populations. Further expansion and contact may well erase the existing skeletal differences of individuals in these populations.

Sex‐biased resource allocation in ovo in a sexually size‐dimorphic species

“…In this study, we used molecular sexing of 72 h old embryos to test whether eggs containing male ring‐ billed gulls Larus delawarensis contain more resources in the form of yolk or albumen than eggs containing female embryos. In ring‐billed gulls, adult males are ca 15% heavier and structurally larger than females (Termaat and Ryder 1984, Ryder 1993), and the larger sex may require more resources during development. Because males are the larger sex in this species, we predicted that eggs containing male embryos would be larger and richer in resources than eggs containing female embryos, to provide male chicks with an advantage at hatching.…”