Early Life Conditions and Immune Defense in Nestling Swainson's Hawks.

The quality of perinatal conditions directly influences the physical and immunological development of nestlings, yet it is inherently variable across space and time. Long-term breeding data for a population of Swainson's hawks (Buteo swainsoni) in northern California show a continuum of territory occupancy and productivity values of individual territories and nests. Here we explore effects of variation among territories on immune system development. We hypothesize that nestlings benefitting from favorable conditions will invest in stronger immune systems, a trait with long-term benefits. We used two immunological assays, a bactericidal assay and a hemolytic-complement activity assay, with leukocyte differentials (heterophil∶lymphocyte ratio) to evaluate the constitutive innate immune system. We examined whether early brood-rearing conditions (i.e., number of siblings, hatch date, endoparasite prevalence) were associated with immunological development. Linear mixed-effects models indicated a positive relationship between extended territory occupancy history-an index of habitat quality-and nestling immune function during years with poorer reproduction. There was no association during an exceptionally good reproductive year. Hence, at least under some circumstances, nestling environments or territory characteristics may affect immune function of nestlings. Our study contributes to the growing body of evidence highlighting the importance of facultative allocation to immune traits using long-term demographic data of a top avian predator.

Health evaluation of Galapagos Hawks (Buteo galapagoensis) on Santiago Island, Galapagos.

Galapagos Hawks (Buteo galapagoensis), the only endemic, diurnal raptor species in Galapagos, are currently distributed on eight Galapagos Islands having been extirpated from three of the human-inhabited islands. In January 2009, we performed health assessments of 89 Galapagos Hawks on Santiago Island, Galapagos. Four of the 89 Galapagos Hawks (4%) evaluated had physical abnormalities. Blood parameters did not differ between males and females, except for aspartate transaminase values, which were significantly higher in females than males. No Galapagos Hawks tested positive for antibodies to avian encephalitis virus, Marek virus, and paramyxovirus-1 or to haemosporidian antigen. Chlamydophila psittaci antigen was detected in 2 of 86 Galapagos Hawks (2%), with 24 of 43 Galapagos Hawks (56%) antibody-positive for avian adenovirus-1 and 1 of 48 Galapagos Hawks (2%) antibody positive for Toxoplasma gondii. There were no significant differences in infectious disease results based on sex. This study contributes to the understanding of the health status of the Galapagos Hawk and to the establishment of baseline information for the species.

Reduced MHC and neutral variation in the Galápagos hawk, an island endemic.

BACKGROUND: Genes at the major histocompatibility complex (MHC) are known for high levels of polymorphism maintained by balancing selection. In small or bottlenecked populations, however, genetic drift may be strong enough to overwhelm the effect of balancing selection, resulting in reduced MHC variability. In this study we investigated MHC evolution in two recently diverged bird species: the endemic Galápagos hawk (Buteo galapagoensis), which occurs in small, isolated island populations, and its widespread mainland relative, the Swainson's hawk (B. swainsoni). RESULTS: We amplified at least two MHC class II B gene copies in each species. We recovered only three different sequences from 32 Galápagos hawks, while we amplified 20 unique sequences in 20 Swainson's hawks. Most of the sequences clustered into two groups in a phylogenetic network, with one group likely representing pseudogenes or nonclassical loci. Neutral genetic diversity at 17 microsatellite loci was also reduced in the Galápagos hawk compared to the Swainson's hawk. CONCLUSIONS: The corresponding loss in neutral diversity suggests that the reduced variability present at Galápagos hawk MHC class II B genes compared to the Swainson's hawk is primarily due to a founder event followed by ongoing genetic drift in small populations. However, purifying selection could also explain the low number of MHC alleles present. This lack of variation at genes involved in the adaptive immune response could be cause for concern should novel diseases reach the archipelago.

Disease ecology in the Galápagos Hawk (Buteo galapagoensis): host genetic diversity, parasite load and natural antibodies.

An increased susceptibility to disease is one hypothesis explaining how inbreeding hastens extinction in island endemics and threatened species. Experimental studies show that disease resistance declines as inbreeding increases, but data from in situ wildlife systems are scarce. Genetic diversity increases with island size across the entire range of an extremely inbred Galápagos endemic bird, providing the context for a natural experiment examining the effects of inbreeding on disease susceptibility. Extremely inbred populations of Galápagos hawks had higher parasite abundances than relatively outbred populations. We found a significant island effect on constitutively produced natural antibody (NAb) levels and inbred populations generally harboured lower average and less variable NAb levels than relatively outbred populations. Furthermore, NAb levels explained abundance of amblyceran lice, which encounter the host immune system. This is the first study linking inbreeding, innate immunity and parasite load in an endemic, in situ wildlife population and provides a clear framework for assessment of disease risk in a Galápagos endemic.