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- Title
Clutch and egg size of Tree Swallows along an elevational gradient.
- Authors
Johnson, L. Scott; Iser, Katherine M.; Molnar, Haley A.; Nguyen, Andre V.; Connor, Chelsea L.
- Abstract
Abstract: How avian reproductive behavior changes at high elevations, and whether changes are the result of adaptation or constraint remains unclear. We compared clutch and egg sizes in two populations of Tree Swallows (Tachycineta bicolor), one at an elevation of ~2500 m a.s.l. in Wyoming's Bighorn Mountains and the other at ~1350 m at the base of these mountains. Females at the high‐elevation site began laying 10 d later, on average, than females at the lower site. Females at the high site laid an average of 0.4 fewer eggs than those at the low site, a significant difference. Eggs were also slightly (2.3%), but significantly, smaller at the high site. Smaller clutches and eggs at the high site may have resulted in part from greater energetic constraints on females. Females at this site faced colder, windier weather during egg formation which would have increased thermoregulatory costs while simultaneously reducing the abundance of prey, i.e., flying insects. Laying a relatively small clutch at the high‐elevation site may also be adaptive, however. Having a smaller brood could help ensure there is an adequate supply of food for each offspring during bouts of inclement weather that are more severe at higher elevations. Also, if the delay in breeding inherent at high elevations reduces the survival prospects of the young, then producing fewer young could enhance a female's chances of breeding again, perhaps at a different location.
- Subjects
TREE swallow; BIRD ecology; SPECIES; AGRICULTURAL egg production; BIRD breeding
- Publication
Journal of Field Ornithology, 2018, Vol 89, Issue 3, p234
- ISSN
0273-8570
- Publication type
Article
- DOI
10.1111/jofo.12262