Island Life Shapes the Physiology and Life History of Eastern Bluebirds (Sialia sialis)

Abstract

Island organisms face a range of extrinsic threats to their characteristically small populations. Certain biological differences between island and continental organisms have the potential to exacerbate these threats. Understanding how island birds differ from their continental relatives may provide insight into population viability and serve as a predictive tool for conservation efforts. We compared an eastern bluebird population in Ohio with a threatened population in Bermuda in terms of the birds' development, morphology, immunology, and reproduction. These comparisons revealed that island nestlings had shorter wings and island adults had longer wings than their continental analogs. Island nestlings also had shorter tarsi than continental nestlings at day 8 posthatch, but this difference was absent at day 15 and in adults. Adults weighed less in Bermuda than in Ohio, and both nestlings and adults in Bermuda exhibited higher levels of two immunological indexes (concentrations of an acute-phase protein and titers of nonspecific antibodies). Clutch sizes and hatch rates did not differ between the island and continental populations; however, as the breeding season progressed, brood sizes declined in Bermuda, whereas no such decline occurred in Ohio. Despite these differences and differences in nestling development, island and continental parents fed their nestlings at equal rates. Overall, our results suggest that the Bermuda phenotype may be adjusted to certain aspects of the island environment but not to others. Efforts to conserve the bluebirds of Bermuda may be improved by focusing on the intraseasonal patterns in nestling mortality and, more generally, the survival probabilities of different age classes.

Geographical and temporal variation in environmental conditions affects nestling growth but not immune function in a year-round breeding equatorial lark

“…Furthermore, while varying substantially among individual nestlings, the indices did not significantly covary with nest index or rain within Kedong. The reliance on measurements at a single time point (i.e., day 10) can complicate comparisons among locations and through time, since the immune systems of nestlings, including components measured in the current study, may develop at different rates across individuals or populations e.g., [69]. Immunity of nestlings may partly reflect the immunological status of their parents [38, 39, 70].…”

Macroimmunology: The drivers and consequences of spatial patterns in wildlife immune defence

“…Spatial studies of urbanization can also test how defence differs between island and mainland populations. Passerine studies have tested the prediction that islands have lower parasite pressure that, in turn, lowers immune investment (Lindström, Foufopoulos, Pärn, & Wikelski, ), although comparative and case studies have found weak or opposite patterns (Matson, ; Matson, Mauck, Lynn, & Irene, ). As urbanization can reduce connectivity (Munshi‐South & Kharchenko, ), urban–rural sampling gradients could provide additional assessments.…”

No island-effect on stress for a rodent from a near-shore archipelago

“…White-footed mice do not display island syndrome in the Thousand Islands Despite the tendency for island wildlife to display morphological and physiological adaptations to insularity (Matson et al, 2014;Holding et al, 2014;Spencer et al, 2017), white-footed mice in the Thousand Islands did not differ in any of these characteristics from their mainland conspecifics. White-footed mice on islands did not display higher relative abundance than mainland mice in disagreement with the general prediction that rodents exhibit particularly high densities on islands (Adler & Levins, 1994;Crespin, Duplantier & Granjon, 2012;, which has been observed for other small vertebrates as well (Novosolov, Raia & Meiri, 2013;Sale & Arnould, 2013).…”