Summary Bird bills have been the subject of classic evolutionary studies that demonstrate how morphological adaptations are driven by foraging ecology. As significant areas of heat loss, bills are also under selection with respect to thermoregulation, yet the ecological consequences of this function have been largely ignored until recently. Given the role of bills in thermoregulation is important, we predict that birds should behave to minimise heat loss through their bills at lower ambient temperatures by attempting to insulate their bill in their plumage. Our second prediction is that this thermoregulatory behaviour should be utilised more by species with relatively larger bills, because they will be more prone to heat loss. We demonstrate both these predictions to be correct using field observations and a comparative analysis of nine shorebird species. First, the placement of the bill within the back plumage while roosting (‘back rest’ behaviour), which insulates the bill, becomes more frequent at cooler temperatures. Second, species with large bills relative to their body size do indeed use back rest behaviour more frequently across a range of temperatures. Our findings show that behavioural thermoregulation can be mediated by bill size, and that bill morphology is not only relevant to foraging ecology but also influences behavioural adaptations to climate. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12814/suppinfo is available for this article.

Predation has driven the evolution of diverse adaptations for defence among prey, and one striking example is the deimatic display. While such displays can resemble, or indeed co-occur with, aposematic ‘warning’ signals, theory suggests deimatic displays may function independently of predator learning. The survival value of deimatic displays against wild predators has not been tested before. Here we used the mountain katydid Acripeza reticulata to test the efficacy of a putative deimatic display in the wild. Mountain katydids have a complex defence strategy; they are camouflaged at rest, but reveal a striking red-, blue-, and black-banded abdomen when attacked. We presented live katydids to sympatric (experienced) and allopatric (naive) natural predators, the Australian magpie Cracticus tibicen, and observed bird reactions and katydid behaviors and survival during repeated interactions. The efficacy of the katydids’ defence differed with predator experience. Their survival was greatest when faced with naïve predators, which provided clear evidence of the protective value of the display. In contrast, katydid survival was consistently less likely when facing experienced predators. Our results suggest that sympatric predators have learned to attack and consume mountain katydids despite their complex defense, and that their post-attack display can be an effective deterrent, particularly against naïve predators. These results suggest that deimatism does not require predator learning to afford protection, but that a predator can learn to expect the display and subsequently avoid it or ignore it. That sympatric predators learn to ignore the defense is a possible explanation for the mountain katydid’s counter-intuitive behavior of revealing warning colors only after tactile stimuli from predator attack.

The function of standing on one leg in birds has long been attributed to reducing heat loss from the unfeathered legs to the external environment. Whilst a handful of single‐species studies correlate the use of the behaviour with ambient temperature, the degree to which it is used across taxa is unknown. Given that leg‐length varies between species, the length of the leg (relative to body size) may mediate the use of this thermoregulatory behaviour, such that birds with longer legs should roost on one leg more than those with relatively shorter legs at any given ambient temperature. We tested this prediction through field observations and comparative analyses of nine shorebird species, with varying tarsi length relative to body size. Six of the nine species examined used unipedal standing more as temperatures decrease, indicating its role as a heat conservation behaviour. We also found that species with relatively longer legs roosted on one leg more frequently across a wide range of temperatures. Species with shorter leg lengths likely rely less on this posture to insulate the relatively smaller surface area of the legs. Our findings showed that the long accepted notion that birds stand on one leg more at colder temperatures holds, and that species with smaller relative leg length were less reliant on this behaviour to minimise heat loss from these bare appendages.

1. Wetlands, and the species that rely upon them, are under significant threat worldwide , with wetlands often being completely removed or drastically altered. Successful wetland management requires an understanding of the interactions between wetland species and the microhabitats they use. The use of microhabitats for thermoregulation in wetland species is poorly studied, though anthropogenic influence on wetlands can reduce the diversity of microhabitats and thus the thermoregulatory options for animals. At high ambient temperatures birds may use the waterlogged wetland margins to help with thermoregulation, and are often observed roosting in the sitting position within this microhabitat. However, whether sitting on the wet substrate helps in thermoregulation is unknown.