Elevated temperatures reduce discrimination between conspecific and heterospecific sexual signals

Heat waves are rapidly increasing in frequency and length around the globe. These periods of elevated temperatures are inducing extreme thermal stress in many organisms. One dramatic result of heat waves is mass mortality events, notably in birds. Although much attention is given to lethal events, little is known about how more common sublethal temperatures affect behaviour, especially in endotherms. For example, male song sparrows, Melospiza melodia atlantica, sing at lower rates at higher temperatures. We hypothesized that simulated heat waves may also reduce the ability of females to discriminate between sexual signals. We tested this hypothesis by quantifying whether female zebra finches, Taeniopygia guttata, responded more to conspecific song or heterospecific song while at their typical housing temperature compared to temperatures above their upper critical temperature. We collected data on how often the birds selected conspecific over heterospecific songs and how much effort the birds invested in sampling those songs using a matched-pairs design. During housing temperature trials, females preferred conspecific song compared to heterospecific song. In contrast, females no longer showed a preference for conspecific song at temperatures above their upper critical limit, although the birds invested similar effort in sampling songs in both treatments. Our findings provide the first experimental evidence that high temperatures affect female preference for a mating signal in an endotherm. Our results highlight the need for future work to investigate this overlooked effect of climate change on endotherms. Because thermoregulatory processes are phylogenetically conserved, our results generate useful predictions for future studies of heat wave effects on mating behaviours in endotherms. (C) 2018 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.