Stress Responsiveness in Nestlings: A Comparison of Two Sampling Techniques

Abstract

I compared the effects on plasma corticosterone levels of two methods of collecting blood samples during standardized capture and handling stress protocols. In one method, individual nestling American Kestrels (Falco sparverius) were bled at three time periods: when initially removed from the nest, and 15 and 30 min later. In the other method, siblings removed from a nest were bled once each, either at the time of removal, or 15 or 30 min later. I found that there was no difference between the two groups in plasma corticosterone levels at the first sampling period, but 15 and 30 min after capture the singly-bled birds had significantly higher plasma corticosterone levels than the multiply-bled nestlings. The results suggest that data from multiplybled birds underestimate actual circulating hormone levels. The underlying mechanism for this phenomenon is unknown, although it may involve hemodilution.Key words: American Kestrel, stress, corticosterone, hemodilution, nestlings Organisms experiencing stressors typically secrete glucocorticoids to maintain or restore homeostasis (Wingfield and Romero 2001). The pattern of corticosterone secretion in response to a standardized stressor frequently is used to compare how different organisms respond to disruptive events. For birds, the most common technique is to use capture and handling stress to activate the hypothalamic-pituitary-adrenal (HPA) axis, with the sensitivity of the axis to the stressor determined through repeated blood sampling followed by radioimmunoassay (RIA) of the blood samples for corticosterone. Birds are held in a cloth bag between sampling sessions. This protocol facilitates comparison of adrenal responsiveness within and among species, and the results of such studies have enhanced our understanding of how ecological factors modulate stress responses (Wingfield et al. 1998, Wingfield andRomero 2001).The importance of a standardized approach in collecting blood samples to measure adrenoresponsiveness has been acknowledged, either explicitly or implicitly, in myriad papers. However, subtle, but possibly important, procedural differences occur among studies that use this protocol. For example, in many studies morphological measurements are taken after the last sampling period, so that the only time birds are handled is when blood samples are taken (Wingfield et al. 1992, Silverin et al. 1997, Blas et al. 2005. In contrast, sometimes morphological measurements are taken in between blood samples, when the birds would otherwise be in a cloth bag (Meddle et al. 2003, Adams et al. 2005. Similarly, occasionally birds are held in small cages in between sampling periods (e.g., Love et al. 2005) rather than in cloth bags. Furthermore, different trapping methods may be utilized in the same investigation (e.g., Lynn et al. 2003). In addition, in most studies similar amounts of blood are removed at each sampling period, but in others the initial blood sample may be larger, if additional hematological measurements are performed (e.g., Clinchy et al. 2004)....

Early Language Milestones and Specific Language Impairment

“…Validity of responses to the language milestone questions was examined through assessment of the examples of first words and word combinations the parents provided in the case history forms. The observers were asked to rate acceptability of examples as true instances of first words or word combinations using a 5-point Likert-type scale (1 = totally unacceptable , 2 = unacceptable , 3 = neutral , 4 = acceptable , and 5 = perfectly acceptable ; adapted from Vagias, 2006). The median rating across the two observers was 5 for first words indicating that these examples were generally perfectly acceptable and 4 for first word combinations indicating that these examples were generally acceptable.…”

Food availability is expressed through physiological stress indicators in nestling white ibis: a food supplementation experiment

“…On sampling days, nestlings were removed from nests and taken to an adjacent shady site to minimize stress of sampled nestlings and disturbance of local nests. Because blood samples could not be obtained in less than 3 min to achieve a baseline level of PCORT (Romero & Reed 2005), we standardized holding time (5 min) for nestlings before sampling, recognizing that standard capture‐and‐handling stress protocols may in fact underestimate the stress response due to haemodilution (Duffy 2008). We collected up to 1 mL of blood from the brachial or jugular veins using a 27·5‐gauge needle.…”

Effects of developmental conditions on nestling American Kestrel (Falco sparverius) corticosterone concentrations

“…We sampled stress-induced CORT at 15 min because previous research on juvenile kestrel CORT secretion patterns showed that most birds reached maximum CORT concentrations within 10-20 minutes [19,25]. We did not bleed the same birds twice to avoid underestimating CORT levels [15]. If a brood consisted of one nestling, we collected only baseline from this individual.…”