Biology ETDs

Publication Date

Fall 11-12-2018

Abstract

Birds in subtropical deserts face significant thermoregulatory challenges as environmental temperatures regularly exceed avian body temperature. To understand the differing susceptibility of desert birds to increasing temperatures, this dissertation initially examined thermoregulatory performance in seven passerine bird species varying in body mass from 10 to 70g – Lesser Goldfinch, House Finch, Pyrrhuloxia, Cactus Wren, Northern Cardinal, Abert’s Towhee and Curve-billed Thrasher – and three larger Sonoran Desert nesting bird species – Mourning Dove (104 g), White-winged Dove (147 g) and Gambel’s Quail (161 g). Daytime resting metabolism, evaporative water loss and real-time body temperature were measured using flow-through respirometry at air temperatures (Tair) from 30° to 66°C. Marked increases in resting metabolism were found at the upper critical temperature (Tuc), which for six of the seven passerine species fell within a relatively narrow range (Tair=36.2° - 39.7°C), but which was considerably higher in the largest, the Curve-billed Thrasher (42.6°C); the Tuc of the quail (41.1°C) was similar to that of the thrasher but considerably lower than in both dove species (45.9° - 46.5°C). Resting metabolism and evaporative water loss were minimal below the Tuc and increased with Tair above the Tuc in all species to maximum values of 0.38 - 1.62 W and 0.87 - 4.02 g H2O hr-1, respectively, among the passerines, 0.94 W and 3.21 g H2O hr-1 in the Gambel’s Quail, and 0.77 - 1.17 W and 3.73 - 6.59 g H2O hr-1 in the Mourning and White-winged Doves. The passerines maintained relatively high rates of resting metabolism and evaporative water loss and reached heat tolerance limits (HTL) that did not scale with body mass but were ~50°C for all species. Gambel’s Quail maintained low resting metabolic rates and low rates of evaporative water loss and reached their HTL at Tair of 52°C. Mourning Doves and White-winged Doves maintained low resting metabolic rates, but high rates of evaporative water loss and reached their HTL at Tair of 58° - 60°C. Body temperatures reached maximum values of 43.5° to 45.3°C in the passerines, 43.6°C in Gambel’s Quail but only 41.9° - 42.7°C in Mourning and White-winged Doves. Among the passerines the ratio of evaporative heat loss to metabolic heat production reached maximum values ranging from 1.39-2.06, similar to that found here for the quail (2.14) but much lower than that found for the doves (3.08-3.69).

Desert birds reduce their activity during the heat of the day, supporting predictions that daily activities and thus fitness and survival will be increasingly impacted by climate warming. Improving confidence in these predictions requires a detailed, mechanistic understanding of functional limits on activity and variability in these limits across taxa. The Heat Dissipation Limit (HDL) theory posits that levels of activity are determined by maximal rates of heat dissipation. This dissertation next examined how high air temperatures, the capacity for evaporative heat loss (EHL) and resting metabolic rate (RMR) restrict activity in 13 species of Sonoran Desert birds. It found that the primary pathway relied upon for evaporative cooling (panting, gular flutter, cutaneous) and its metabolic efficiency (EHL/RMR) predict variation in sustained metabolic scope in the heat. Among nightjars and doves, which use gular flutter and cutaneous water loss, respectively, EHL carries very low metabolic costs. These species can sustain much higher workloads in the heat than passerines, which depend upon the metabolically more costly pathway of panting to achieve evaporative cooling. Climate warming will increasingly impact the activities of all desert birds, but this new model suggests that the impacts to desert passerines will be disproportionately high.

Language

English

Keywords

birds, body temperature, heat dissipation limit theory, resting metabolism, Sonoran Desert, evaporative cooling

Document Type

Dissertation

Degree Name

Biology

Level of Degree

Doctoral

Department Name

UNM Biology Department

First Committee Member (Chair)

Blair O. Wolf

Second Committee Member

Alexander R. Gerson

Third Committee Member

Janet M. Ruth

Fourth Committee Member

Christopher C. Witt

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