Year of Award

2021

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Thomas E. Martin

Commitee Members

Jedediah Brodie, Erick Greene, Creagh Breuner, Bret Tobalske

Keywords

energy expenditure, life history theory, nest structures, offspring growth and development, parental behavior, rainfall effects on ontogeny

Publisher

University of Montana

Abstract

Weather creates energetic and survival challenges for organisms that can influence demography. Harsh weather often causes increased energy expenditure in adults, but how weather affects other life stages is less well understood. Juveniles are especially vulnerable because they must use energy to survive weather effects and maintain growth and development while having poorly developed thermoregulatory capabilities. Juveniles that spend energy overcoming harsh weather can have delayed growth and maturation, which can negatively affect competitive abilities, survival, and lifetime fitness. Understanding weather effects on offspring is particularly challenging in altricial species because parents have evolved strategies to ameliorate such effects. However, the degree to which parents ameliorate harmful effects of weather on offspring varies within and across species due to environmental and evolutionary constraints. Our ability to predict accurate ecological ramifications of climate change are currently limited by a paucity of studies of weather effects on developing offspring, and how parents are able and willing to mitigate these effects. This dissertation aims to fill such gaps in knowledge using empirical data within and across species of songbirds on 3 continents.

In chapter 1, I tested whether slower growth and development of organisms living at high elevations is caused by harsh weather. At a study site at ca. 3200 m asl in Malaysian Borneo, I found that Mountain Blackeye (Chlorocharis emiliae) parents in experimentally heated and covered nests warmed their young less and provisioned more often. This behavioral plasticity resulted in faster mass gain and wing growth, and earlier fledging of young. Thus, slower growth and development of montane organisms partially reflects proximate responses to harsh weather.

In chapter 2, I used samples from 664 nestlings across 54 species on 3 continents to test for proximate and evolutionary sources of offspring daily energy expenditure (DEE). Within species, heavier rain, colder Ta, and fewer siblings were each correlated with higher nestling DEE, highlighting the importance of weather and huddling with siblings on offspring energy use. Across species, DEE was positively correlated with adult and juvenile mortality, illustrating the evolved component of DEE that can be shaped by selection from age-specific mortality.

In chapter 3, I simulated rain above nests of 5 species of songbirds in Malaysian Borneo to test the direct effects of rain on offspring DEE and parental behavior, and how these responses varied across nest type. Parents in enclosed nests did not change their behavior in response to rain, while parents in open nests brooded their young more, leading to no difference in nestling DEE in either nest type. These results suggest that parents using exposed nest types can ameliorate costs of short-term rain on young through behavioral plasticity. These results also suggest that parents using open nests may need to modify their behavior in locations where rain is predicted to increase from climate change.

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© Copyright 2021 Adam Elliot Mitchell