Too much hot air? Informing ethical trapping in hot, dry environments.

Context. Trapping of small vertebrates during their active hot summer periods is vital for conservation and impact assessment studies. Animal Ethics Committees (AECs) protect wildlife by enforcing arbitrary but restrictive temperature limits for trapping. Aims. Empirical data were gathered on the temperatures reached in different trap configurations to inform pragmatic ethical guidelines. Methods. Temperature was measured inside small vertebrate traps at two Australian arid zone sites to generate data on the thermal consequences of: (1) trap design and external shading; (2) provision of protective refuge substrates; and (3) timing of trap clearing. Key results. Shading and increased trap depth significantly reduced temperatures within pitfall traps. A conservative stressful upper temperature limit of 36°C was never exceeded inside deep, shaded, narrow pitfall traps at one study site and only between 1100 and 1300 hours on 3 days at the hotter site, despite ambient temperatures reaching over 42°C. By contrast, potentially lethal upper temperatures were reached in wider, shallower bucket pit traps on most days at both sites, even when optimal shading and refuge substrates were employed. Deployment of surface traps under vegetation and with additional shading significantly reduced maximum temperatures experienced. Temperatures inside shaded Elliott and funnel traps generally tracked ambient air temperatures and thus typically exceeded conservative threshold temperatures between 0700 and 1900 hours when ambient temperatures exceeded 36°C. Conclusions. Temperatures experienced in optimal deep, shaded traps when ambient temperatures exceeded 40°C were 31°C lower than surface temperatures and similar to temperatures recorded at 20 cm below the soil surface, where many species would typically take refuge at these times. Implications. Data suggest that deep (60 cm), narrow pitfall traps with elevated lids for shade and shelter substrate inside should enable trapping to be conducted safely in the study region during summer (December to February). This is even the case in extremely hot weather, as long as trapped animals are removed within 4 h of sunrise. Ecophysiological studies of thermal tolerance within optimum trap arrangements revealed by the present study will allow field ecologists and AECs to develop informed site-specific trapping protocols. [ABSTRACT FROM AUTHOR]