Seasonal variation in chronic stress and energetic condition in Gray Catbirds (Dumetella carolinensis) and Song Sparrows (Melospiza melodia)

Seasonal variation in sex-specific immunity in wild birds

“…In addition, because males are in general more aggressive and dominant than females, in periods of low food abundance (such as winter) males could secure their access to food over females, which seems to cause strain in birds 70 – 72 . This could explain our results for H/L ratio, since increments in H/L ratio appear to be associated with sustained stress in birds 35 , 40 , 73 . Although the H/L ratio was not sex-biased during the non-breeding or the breeding season, both estimates were different from each other, and males experienced a greater change between the seasons than females.…”

Refueling performance of migratory passerines stopping at an inland stopover site in the Connecticut River Valley

“…White-throated Sparrows and Swainson's Thrushes captured at the same stopover site in spring and fall do not vary in mean body mass between seasons (Smith 2013). The body mass (or body mass index) of Gray Catbirds, however, is significantly increased during fall migration compared to spring migration as well as the wintering and breeding periods (Oberkircher and Pagano 2018, DeMoranville et al 2019). The elevated TRIG we saw for catbirds during fall migration may be related to the documented increase in body mass in the fall for this species specifically.…”

“…The elevated TRIG we saw for catbirds during fall migration may be related to the documented increase in body mass in the fall for this species specifically. Additionally, Gray Catbirds display elevated heterophil/lymphocyte ratios in the spring compared to fall and summer, indicating increased stress (Oberkircher and Pagano 2018). Another measure of stress response, corticosterone, has been associated with lower TRIG in migrant birds (Liu and Swanson 2014).…”

Patterns in the physiological condition of three species of thrushes during autumn stopover near the south shore of Lake Ontario

“…Leukocyte profiles were determined by examining each blood smear under 1,0003 oil immersion using a compound light microscope. Cells were counted until the total number of leukocytes reached 100, and then the ratio of heterophils to lymphocytes was calculated (Vleck et al 2000, Seewagen et al 2015, Oberkircher and Pagano 2018), hereinafter “H/L.” Parasites and abnormalities were also noted during the leukocyte count.…”

“…Assessment of immunological condition via differential leukocyte counts may complement such data by providing information on chronic stress levels of individual birds attributed to a variety of relevant factors, including food availability (Davis et al 2008). Leukocyte counts avoid logistical challenges associated with rapid sample collection in free-living birds and have further proven useful in evaluating the health status of migratory birds in relation to their energetic condition, parasite loads, and migration distance (Owen and Moore 2008, Buehler et al 2010, Granthon and Williams 2017), and to investigate seasonal differences in stopover physiology of birds (Oberkircher and Pagano 2018).…”