IMMUNE AND GROWTH RESPONSE OF WESTERN BLUEBIRDS AND ASH‐THROATED FLYCATCHERS TO SOIL CONTAMINANTS

Abstract

During the past two decades, a critical need has developed to determine how exposure to contaminants in the environment affects individual and population processes. In this study, the immunocompetence of Western Bluebirds (Sialia mexicana) and Ash‐throated Flycatchers (Myiarchus cinerascens) was studied on a landscape–soil contaminant gradient at Los Alamos National Laboratory (LANL) in New Mexico during 1997–1999. A variety of contaminants (heavy metals, chemicals, insecticides, polychlorinated biphenyls, and radioactive isotopes) range across different spatial scales and concentrations on LANL land. The two species have similar life‐history traits, except that the Ash‐throated Flycatcher has a faster rate of development and fledges 4–5 days earlier than the bluebird. The number of active nest boxes increased from 1997 to 1998 and 1999 for the Western Bluebird, but not for the Ash‐throated Flycatcher. Survival of nestling flycatchers was lower in areas within 60 m of a potential contaminant release site, with a higher survivorship function associated with boxes farther away. The two species did not differ in their response to antigens, and there was no difference between locations for immunocompetence for either species. Flycatcher nestlings had a higher average cell‐mediated response than bluebird nestlings, as predicted by the faster rate of development of the flycatchers. Phytohemagglutinin response varied between locations for both species. The cell‐mediated effects were dynamic in that, in general, the same locations showed similar patterns for each year. Hematocrits steadily increased with age for both species and varied between locations for the bluebird, but not the flycatcher.