Effect of territory quality on intrusion rate in nonbreeding hummingbirds

Summary Experimental reductions of productivity on feeding territories of Anna's hummingbirds (Calypte anna) decreased intrusion rate. This trend contrasts with the absence of strong correlations between intrusion rate and productivity in previous experimental studies. Consideration of sample sizes, productivity rates, and time-dependent influences on intrusion rate (e. g., day-to-day changes in weather) indicates that this difference resulted from the more natural spatial distribution of artificial flowers used in this study. Offprint requests to: P.W. Ewald     

Torpor and basking in a small arid zone marsupial

The high energetic cost associated with endothermic rewarming from torpor is widely seen as a major disadvantage of torpor. We tested the hypothesis that small arid zone marsupials, which have limited access to energy in the form of food but ample access to solar radiation, employ basking to facilitate arousal from torpor and reduce the costs of rewarming. We investigated torpor patterns and basking behaviour in free-ranging fat-tailed dunnarts Sminthopsis crassicaudata (10 g) in autumn and winter using small, internal temperature-sensitive transmitters. Torpid animals emerged from their resting sites in cracking soil at ∼1000 h with body temperatures as low as 14.6°C and positioned themselves in the sun throughout the rewarming process. On average, torpor duration in autumn was shorter, and basking was less pronounced in autumn than in winter. These are the first observations of basking during rewarming in S. crassicaudata and only the second direct evidence of basking in a torpid mammal for the reduction of energetic costs during arousal from torpor and normothermia. Our findings suggest that although overlooked in the past, basking may be widely distributed amongst heterothermic mammals. Therefore, the energetic benefits from torpor use in wild animals may currently be underestimated.