Effects of radio-transmitters on fecal glucocorticoid levels in captive dickcissels

We determined the effects of a leg-harness transmitter on fecal glucocorticoid levels of wild male Dickcissels (Spiza americana) in captivity. During the postbreeding season of 2001, we captured 10 male Dickcissels in central Missouri and housed them in individual pens of an outdoor aviary. We radio-tagged five birds; the other five were captured and handled, but were not radio-tagged. We collected fecal samples every other day prior to attachment (31 July-21 August) and after attachment (24 August-20 September). Body condition and morphology were similar between control and transmitter-equipped birds. We observed a significant interaction between transmitter attachment and time since attachment. Compared to baseline levels, fecal glucocorticoid metabolites were significantly lower in control (6.1 ± 13.7 ng g ^-1) than transmitter-equipped (102.3 ± 13.7 ng g ^-1) birds during the first 24 hr after attachment. Although transmitter-equipped birds showed elevated fecal glucocorticoid levels, the response was acute and returned to baseline levels within 48 hr.