Effects of captivity and testosterone on the volumes of four brain regionsin the dark-eyed junco (Junco hyemalis)

This study investigates the effects of captivity and testosterone treatment on the volumes of brain regions involved in processing visual and spatial information in adult dark-eyed juncos (Junco hyemalis). We treated captive and free-living male juncos with either testosterone-filled or empty implan ts. Captive juncos had a smaller hippocampal formation (HF) (both in absolu te volume and relative to telencephalon) than free-living birds, regardless of hormone treatment. Testosterone-treated males (both captive and free-li ving) had a smaller telencephalon and nucleus rotundus, but not a smaller H F or ectostriatum, than controls. We found that free-living testosterone-tr eated males had larger home ranges than free-living controls in agreement w ith earlier experiments, but we found no corresponding difference in HF vol ume. We discuss the implications of the effect of captivity on HF volume fo r past and future laboratory experiments. (C) 2000 John Wiley & Sons, Inc.