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Urban rooftop-nesting Common Nighthawk chicks tolerate high temperatures by hyperthermia with relatively low rates of evaporative water loss

Ornithological Applications, 2021-08, Vol.123 (3), p.1-13 [Peer Reviewed Journal]

Copyright © American Ornithological Society 2021. All rights reserved. For permissions, e-mail: journals.permissions@oup.com. journals.permissions@oup.com ;Copyright American Ornithological Society Aug 1, 2021 ;ISSN: 0010-5422 ;EISSN: 2732-4621 ;EISSN: 1938-5129 ;DOI: 10.1093/ornithapp/duab016

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  • Title:
    Urban rooftop-nesting Common Nighthawk chicks tolerate high temperatures by hyperthermia with relatively low rates of evaporative water loss
  • Author: Newberry, Gretchen N. ; O'Connor, Ryan S. ; Swanson, David L.
  • Subjects: Ambient temperature ; Birds ; Body mass ; Body temperature ; Caprimulgiformes ; chick ; Chickens ; Chicks ; Chordeiles minor ; Climate change ; Dew point ; Evaporative cooling ; evaporative water loss ; Exposure ; Flutter ; Heat ; Heat stress ; Heat tolerance ; High temperature ; Humidity ; Hyperthermia ; Juveniles ; Land use ; masa corporal ; Nesting ; Nests ; nighthawk ; Oxygen consumption ; polluelo ; pérdida de agua por evaporación ; RESEARCH ARTICLE ; Summer ; Temperature ; termorregulación ; thermoregulation ; Upper bounds ; urban ; Urban areas ; urbano ; Vibration ; Water loss
  • Is Part Of: Ornithological Applications, 2021-08, Vol.123 (3), p.1-13
  • Description: Heat tolerance for many birds under climate and land use change scenarios could be compromised in the future. Common Nighthawks (Chordeiles minor) belong to the Caprimulgiformes, a generally heat-tolerant order, but few studies have assessed heat tolerance in Caprimulgiform chicks, which might be particularly susceptible to heat stress. In the midwestern United States, nighthawks primarily nest on flat graveled rooftops in urban areas, as natural nesting habitats are limited. Urban rooftop-nesting nighthawks are likely exposed to higher environmental temperatures than birds nesting at more thermally buffered natural sites, and evaporative cooling might be impeded by the typically high summer humidity in their Midwest breeding range. This combination of heat and humidity might negatively impact heat tolerance of nighthawk chicks. We exposed 7- to 14-day-old nighthawk chicks (n = 15) from rooftop nests to ambient temperatures (Tas) up to 51°C and at typical summer dew points. Chicks initiated gular flutter at a mean ambient temperature of 42.4 ± 3.4°C (mean ± SE). Evaporative water loss (EWL) rates increased significantly with increasing temperature above 44.0 ± 1.5°C. Chicks showed little evidence of lower and upper bounds of the thermal neutral zone over the range of temperatures (30–44°C) for which we measured oxygen consumption. Body mass loss was significantly positively correlated with temperature during heat exposure trials. Chicks tolerated Tas up to 51°C and body temperatures (Tbs) up to 48°C, which, along with the high temperatures at which gular flutter and high rates of EWL were initiated, suggest that nighthawk chicks are tolerant of high ambient temperatures, even with relatively high humidity. Given the high rates of mass loss and high Tbs at hot ambient temperatures, chick heat tolerance mechanisms could be detrimental for rooftop-nesting nighthawks given projected increasing trends for both heat and humidity in the midwestern United States. LAY SUMMARY Climate and land use trends may interact to stress physiological capacities for avian heat tolerance. Common Nighthawks belong to the heat-tolerant nightjar order and, in the midwestern United States, nest almost exclusively on hot and humid urban rooftops. We exposed 7- to 14-day-old chicks to laboratory conditions simulating their rooftop thermal environment and measured rates of oxygen consumption, evaporative water loss (EWL), and body temperature (Tb). Chicks survived ambient temperatures up to 51°C and Tbs up to 48°C with comparable rates of EWL under heat exposure to adults but EWL resulted in body mass loss. Chicks were hyperthermic under heat exposure, suggesting that increases in Tb help reduce EWL. Thermoregulation under hot, humid conditions, which are projected to increase in the future, might precipitate a decline in urban nighthawk populations, despite their capacity for heat tolerance.
  • Publisher: Chicago: University of California Press
  • Language: English;Spanish
  • Identifier: ISSN: 0010-5422
    EISSN: 2732-4621
    EISSN: 1938-5129
    DOI: 10.1093/ornithapp/duab016
  • Source: Freely Accessible Journals
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