VEGETATIVE AND THERMAL ASPECTS OF ROOST-SITE SELECTION IN URBAN YELLOW-BILLED MAGPIES

Abstract

We examined vegetative and thermal aspects of roost-site selection in urban Yellow-billed Magpies (Pica nuttalli) in Sacramento, California, from winter 2003 to spring 2004. Vegetation used for roosting included cultivated species such as glossy privet (Ligustrum lucidum), English ivy (Hedera helix), and white mulberry (Morus alba), and native species such as interior live oak (Quercus wislizeni), valley oak (Q. lobata), and California laurel (Umbellularia californica). Percent canopy cover was consistently high (mean = 94% ± 1.9 SD). Mean roost height was 9.7 m ± 3.5 SD and the mean height at which magpies roosted was 6.6 m ± 2.0 SD. Communal roosts were generally located within or near riparian corridors. Magpies roosted in relatively warm microhabitats, but they did not appear to obtain a thermal advantage by roosting communally. The timing of roost occupancy was restricted primarily to times when the roost was thermally advantageous.