Time constraints in temperate-breeding species: influence of growing season length on reproductive strategies


  • K. E. B. Gurney,

  • R. G. Clark,

  • S. M. Slattery,

  • N. V. Smith-Downey,

  • J. Walker,

  • L. M. Armstrong,

  • S. E. Stephens,

  • M. Petrula,

  • R. M. Corcoran,

  • K. H. Martin,

  • K. A. DeGroot,

  • R. W. Brook,

  • A. D. Afton,

  • K. Cutting,

  • J. M. Warren,

  • M. Fournier,

  • D. N. Koons

K. E. B. Gurney (kirsty.gurney@usask.ca) and R.G. Clark, Univ. of Saskatchewan, Dept of Biology, 112 Science Place, Saskatoon, SK S7N5E2, Canada. (Present address of RGC: Environment Canada, Prairie and Northern Wildlife Research Centre, SK S7N0X4, Canada.) – S. M. Slattery and L. M. Armstrong, Ducks Unlimited Canada, Inst. for Wetland and Waterfowl Research, MB R0C2Z0, Canada. – N. V. Smith-Downey, Univ. of Texas at Austin, Jackson School of Geosciences, TX 78713, USA. – J. Walker and K. A. DeGroot, Univ. of Alaska Fairbanks, Inst. of Arctic Biology and Dept of Biology and Wildlife, AK 99775-7000, USA. (Present address of J W: Ducks Unlimited, Great Plains Regional Office, ND 58503-9011, USA.) – S. E. Stephens, Ducks Unlimited, Great Plains Regional Office, ND 58503-9011, USA.) – M. Petrula, Alaska Dept of Fish and Game, Wildlife Conservation, AK 99518, USA. – R. M. Corcoran, US Fish and Wildlife Service, Kodiak National Wildlife Refuge, AK 99615, USA. – K. H. Martin, US Fish and Wildlife Service, Endangered Species, AK 99701, USA. – R. W. Brook, Ontario Ministry of Natural Resources, Wildlife Research and Development Section, ON K9J 7B8, Canada. – A. D. Afton, US Geological Survey, Louisiana Cooperative Fish and Wildlife Research Unit, LA 70803-6202, USA. – K. Cutting and J. M. Warren, US Fish and Wildlife Service, Red Rock Lakes National Wildlife Refuge, MT 59739, USA. – M. Fournier, Environment Canada, Environmental Conservation Branch, NT X1A1E2, Canada. – D. N. Koons, Utah State Univ., Dept of Wildland Resources and the Ecology Center, UT 84322-5230, USA.


Organisms that reproduce in temperate regions have limited time to produce offspring successfully, and this constraint is expected to be more pronounced in areas with short growing seasons. Information concerning how reproductive ecology of endotherms might be influenced by growing season length (GSL) is rare, and species that breed over a broad geographic range provide an opportunity to study the effects of time constraints on reproductive strategies. We analyzed data from a temperate-breeding bird, the lesser scaup Aythya affinis; hereafter scaup, collected at eight sites across a broad gradient of GSL to evaluate three hypotheses related to reproductive compensation in response to varying time constraints. Clutch initiation date in scaup was unaffected by GSL and was unrelated to latitude; spring thaw dates had a marginal impact on timing of breeding. Clutch size declined during the nesting season, as is reported frequently in bird species, but was also unaffected by GSL. Scaup do not appear to compensate for shorter growing seasons by more rapidly reducing clutch size. This study demonstrates that this species is remarkably consistent in terms of timing of breeding and clutch size, regardless of growing season characteristics. Such inflexibility could make this species particularly sensitive to environmental changes that affect resource availabilities.