Chapter One: Consequences of Investigator Handling On Avian Immune Function and Morphology
Environmental conditions during the neonatal period can affect the growth, physiology, and immune function of birds. In many avian studies, a common potentially stressful experience for neonates is investigator handling. While neonatal handling is known to affect the adult phenotype in rats, the effects of this stressor have rarely been examined in wild avian subjects. During periods of stress, birds increase the plasma titer of corticosterone, a hormone that can affect nestling growth rates and degree of immune function. I examined the effect of neonatal handling on avian growth and immune system development. I subjected American kestrels (Falco sparverius) and European starlings (Sturnus vulgaris) to 15 minutes of daily investigator handling throughout the nestling period, while controls remained undisturbed. Immediately prior to fledging I assessed their cell-mediated immunity, mass, and degree of asymmetry. Handling did not significantly affect any of the measured parameters. I also addressed the possibility that treatment differences would appear only when the birds were challenged with a more substantial stressor by bringing birds into captivity for 24 hours. Captivity did not affect mass but significantly lowered immunocompetence, although this was independent of treatment. Therefore, investigator handling does not affect avian development, although captivity is immunosuppressive, at least temporarily.
Chapter 2: Effects of Elevated Corticosterone Levels on Morphology
Stressors encountered during the normal developmental period may affect an individual’s phenotype, including immunocompetence, growth, and feather quality. I examined effects of chronic, low-level stress on American kestrel (Falco sparverius) nestlings. Continuous release of corticosterone, a hormone involved in the stress response, can model chronic stress in birds. I implanted males with either corticosterone implants or shams and measured their growth, immune function, and feather coloration. I found no significant differences between groups at the end of the exposure period in either morphometrics (mass, tarsus, wing length, asymmetry, and body condition) or immunocompetence (cell-mediated immunity and heterophil/lymphocyte ratio). Additionally, treatment did not affect humoral immunity or feather coloration. One week subsequent to implantation removal, however, previously undetected differences existed. Sham-implanted birds had significantly longer wings while corticosterone-implanted birds had an increased level of cell-mediated immunity. Therefore, it seems that smallincreases in basal corticosterone levels have small, but measurable, effects on avian development.