Thermal Tolerance of Avian Embryos: A Review

Abstract

Avian eggs usually experience temperatures of 30 to 40°C during the incubation period, but eggs often cool to much lower temperatures. Hyperthermia is less common. Passerines do not show higher incubation temperatures than other orders that have been studied extensively. Field measurements of incubation temperatures are usually lower than the optimal temperatures for development found in laboratory studies. Some species regulate egg temperatures closely throughout incubation; but in at least one penguin species, mean egg temperature increases and ranges of egg temperature decrease through the incubation period. Both the optimal temperature for continuous exposure and the range of temperatures producing high survivorship differ among species. Species also differ in their responses to temperature exposures of limited duration. Thus, the use of a "physiological zero" applicable to all species is not warranted. Penguins have both a lower optimum and a broader range of acceptable incubation temperatures than do other species studied. Age, duration, and temperature of exposure significantly affect survivorship. Hyperthermia is evidently more injurious to the developing embryo than is hypothermia. Resistance to cold exposure is a heritable trait, but the genetics and physiology of the response(s) are not known. For older embryos, the physiological effects of hyperthermia are similar to those of adult birds in terms of the organ systems that are first to fail. An estimate of thermal tolerance for short exposures in most species studied is 16 to 41°C and, for exposures lasting several hours, 36 to 39°C.

Causes of reduced clutch size in a tidal marsh endemic

“…In concordance with the temperature hypothesis (T3), more coastal nests (75.6%) than inland nests (40.2%) experienced temperatures above the range of physiological zero reported by Webb (1987) during laying (n = 413, Wald v 1 2 = 44.4, P \ 0.001). This is a direct result of the significantly higher mean daily high temperatures during the breeding season (n = 1102, r 2 = 0.13, f 5,1096 = 32.8, P \ 0.0001) in coastal Delaware (26.0 ± 0.2°C) than in inland Maryland (21.4 ± 0.3°C), controlling for year (f = 10.7, P \ 0.001).…”

“…The effect of nesting attempt number (i.e., the first to fifth nest of a given female), which is well known to correlate with clutch size, was not significant when added to this final model (f 1 = 0.7, P = 0.42). The mean high temperatures during the laying period of inland nests fell below the range of physiological zero for egg development outlined by Webb (1987), while the mean temperatures during laying among coastal nests fell above this range in all but the largest clutches (Fig. 8).…”

“…All eggs except for the last egg are, therefore, subject to variation in ambient temperatures. Assuming that physiological zero is between 24°and 26°C (Webb 1987), development is suspended for eggs that are laid in ambient temperatures below 24°C. For eggs that are laid in conditions above this critical limit and below optimal incubation temperatures (36°C: Cooper et al 2005;Stoleson and Beissinger 1999), partial, slowed development can lead to abnormalities and inviable eggs (Deeming and Ferguson 1992).…”

“…7 The maximum ambient temperature on the first day of laying (mean ± SE) for broods of Melospiza georgiana where all eggs successfully hatched (filled diamonds) or where one or more eggs were inviable (open diamonds), calculated for clutch size. The dashed lines indicate the temperature range of the lower limit for embryonic development outlined by Webb (1987 Fig. 8 The relationship between the daily maximum ambient temperature during laying (mean ± SE) and clutch size in coastal Melospiza georgiana nigrescens (filled circles) and inland M. g. georgiana (open squares), controlling for Julian date and year.…”

Thermal and energetic consequences of nest location and breeding times in Water Pipits (Anthus spinoletta)

“…Johnson & Cowan 1974;Zann & Rossetto 1991;Williams 1993) and cause immediate death of the embryo, sublethal teratogenic effects or slow down development (Webb 1987). There is some evidence in the Water Pipit that low temperatures strain the incubating females' time and energy budgets (Rauter 1996;Rauter & Reyer 1997): (1) Length of the inattentive period increased with decreasing temperature and (2) length of the incubation period increased as the average mean daily air temperature decreased.…”