Heterophil/Lymphocyte Ratio: Stress-Related Environmental Factors in Tree Swallow (Tachycineta bicolor) and Eastern Bluebird (Sialia sialis) Nestlings
Dr. Kathy Winnett-Murray
We used heterophil/lymphocyte (H/L) ratios from nestlings inhabiting artificial nest boxes to investigate the relationship between nestling attributes and stress. We hoped to understand how the (H/L) ratio responds to various environmental factors that could result in elevated stress levels. Dreyer (unpubl. ms. 2005) determined that nestlings of Tree Swallows (Tachycineta bicolor) are more likely to be infected with ectoparasites (mites, lice, ticks and fleas) than are the young of Eastern Bluebirds (Sialia sialis). Similarly, swallow nests usually contain a greater abundance and variety of arthropods, including potential avian ectoparasites, than do bluebird nests. In a variety of birds, an increased H/L ratio is associated with natural stressors; we hypothesized that nestlings that were hatched later in the season, had a greater number of siblings, weighed less and/or had parasites in their nest or were infected themselves would exhibit higher H/L ratios. Similarly, we predicted that swallows would have more infected nests and be more infected directly with parasites than bluebirds, also resulting in higher H/L ratios. We analyzed stained blood smears previously collected in 2005 from nestlings at Consumer’s Energy J.H. Campbell Complex, MI. A leukocyte profile was determined and H/L ratios were calculated based on at least 100 total observed leukocytes for each bird. We will be exploring the association of the previously mentioned nestling attributes on H/L ratios to identify the most important correlates of this widely used indicator of physiological stress.
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