Effects of radiotransmitters on northern goshawks: Do tailmounts lower survival of breeding males?

We used the Cormack-Jolly-Seber model to estimate the effects of radiotransmitters on survival of breeding northern goshawks (Accipiter gentilis). We separately compared apparent annual survival of leg-banded goshawks with (1) tailmount- and (2) backpack-style radiotransmitters (hereafter tailmounts and backpacks) to apparent annual survival of breeding adults with legbands only. The best model without radiotransmitter effects, evaluated with Akaike's Information Criterion (AlC_c), suggested no gender- or year-specific effects on survival. We then added radiotransmitter attachment type (tailmount or backpack) and mass of radiotransmitter as covariates to the base model to estimate the effect of radiotransmitters. Tailmounts on males significantly reduced apparent annual survival from 0.75 (SE = 0.02, 95% Cl: 0.71 to 0.78) without radiotransmitters to 0.29 (SE = 0.15, 95% Cl: 0.09 to 0.63) with radiotransmitters. Backpacks had no significant effect on survival of adults (0.79, SE = 0.17, 95% Cl: 0.33 to 0.97). The strikingly lower survival of goshawks with tailmounts was surprising because tailmounts weighed less (10 g, 1.5% body mass) than backpacks (16-23 g, max = 3.4% body mass) and likely were carried for shorter periods. Due to the small number of goshawks with tailmounts (n = 14) in this study, our results possibly were due to chance. We therefore recommend additional study of the effects of tailmounts on survival of breeding male northern goshawks.