The thermoregulatory role of relative bill and leg surface areas in a Mediterranean population of Great tit (Parus major)

Abstract

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Energetic costs of bill heat exchange demonstrate contributions to thermoregulation at high temperatures in toco toucans (Ramphastos toco)

“…No reuse allowed without permission. association between appendage (e.g., bill, limbs) size and environmental temperatures and, consequently, to heat exchange capability, seems to be quite well supported (Playa-Montmany et al, 2021;Tattersall et al, 2018). This may involve energetic considerations and we posit that bill size will correlate with the amplitude of the TNZ in birds, particularly in the setting of the UCT threshold.…”

“…In this context, bill size has been demonstrated to vary with latitudinal gradient in environmental temperature (i.e., Allen's rule; Symonds and Tattersall, 2010), possibly under the influence of the most critical temperatures experienced at different seasons by different species or populations at different geographic locations (see Danner and Greenberg, 2015). Altogether, an adaptive association between appendage (e.g., bill, limbs) size and environmental temperatures and, consequently, to heat exchange capability, seems to be quite well supported (Playa-Montmany et al, 2021;Tattersall et al, 2018). This may involve energetic considerations and we posit that bill size will correlate with the amplitude of the TNZ in birds, particularly in the setting of the UCT threshold.…”

Behavioural and physiological responses to experimental temperature changes in a long-billed and long-legged bird: a role for relative appendage size?

“…Unfeathered bills, legs and feet are bird appendages that are highly vascularized, and their potential roles in regulating thermal balance are well recognised (e.g., Steen and Steen 1965;Hagan and Heath 1980;Tattersall et al 2009Tattersall et al , 2017Carr and Lima 2012;Cabello-Vergel et al 2021;Playà-Montmany et al 2021). Appendage size may vary among populations of the same bird species according to the thermal environment, and it has been suggested, for example, that a larger bill surface area could be an adaptation to increase dry heat loss under hot climatic conditions .…”

“…Appendage size may vary among populations of the same bird species according to the thermal environment, and it has been suggested, for example, that a larger bill surface area could be an adaptation to increase dry heat loss under hot climatic conditions . However, these appendages may also be a source of heat gain for birds living in extremely hot environments, where the environmental temperature can approach or surpass the T b Gardner et al 2016;Ryeland et al 2017), or of heat loss when exposed to cold (Hagan and Heath 1980;Tattersall et al 2009;Gardner et al 2016), although these aspects of bird thermoregulation are less-known (Gardner et al 2016;van de Ven et al 2016;Ryeland et al 2017Ryeland et al , 2019Benham and Bowie 2021;Playà-Montmany et al 2021).…”

“…Last, we measured the resting metabolic rate (RMR) and EWL of dunlins at different T a values to assess the potential role of relative bill and tarsi sizes in explaining variations in both rates. EWL is a metabolically costly process, so if the appendage surface area can be used as a radiator to expel "dry" heat under thermally stressful conditions , we expected that individuals with larger relative bill and tarsi sizes would consume less oxygen to maintain homeothermy when T a exceeds their thermoneutral zone but below their T b (Playà-Montmany et al 2021).…”