TILMAN-SCHINDEL, E*; KELLY, T; BERZINS, L; HUSSELL, DJT; BOONSTRA, R; BURNESS, G; Watershed Ecosystems Graduate Program, Trent University, Ontario; Biology Department, Trent University, Ontario; Biology Department, Trent University, Ontario; Wildlife Research and Development Section, Ontario Ministry of Natural Resources; Department of Zoology, University of Toronto, Scarborough; Biology Department, Trent University, Ontario: Do avian growth rates, immune function and corticosterone levels vary with insect abundance?

We examined growth, immune response, and basal corticosterone (CORT) levels in tree swallow (Tachycineta bicolor) nestlings over two years (2004 and 2005), and at two sites differing historically in insect abundance. We adjusted all broods to a common size of 6 nestlings. To assess the cell-mediated immune response, we injected phytohaemagglutinin (PHA) into the wing webs of two nestling per nest, followed by measurement of the swelling response 24 hours later. Humoral immune response was studied by vaccinating two nestlings per nest with either sheep red blood cells (SRBC; 2004), or with Newcastle Disease Virus (NDV; 2005). Blood samples were collected 7 days later to measure either anti-SRBC or anti-NDV titres. The remaining two nestlings per nest were blood sampled for determination of basal CORT levels. Nestling growth rates were significantly higher at the breeding site with historically higher insect abundance. Nonetheless, neither CORT levels nor the PHA swelling response differed between the two breeding sites, suggesting little evidence of a trade-off between growth rates and cell-mediated immunity. No antibodies to either SRBCs or NDV were detected in plasma of nestlings, likely as a result of their immature immune system. We suggest that natural variation in insect abundance has minimal effects on cell-mediated or humoral immunity in tree swallow nestlings.