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

Abstract

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.

Endogenous contributions to egg protein formation in lesser scaup Aythya affinis

“…The high elevation (2033 m) of the Centennial Valley provides a narrow growing season for scaup that is shorter in duration to that of more northerly breeding areas where the majority of lesser scaup breed (i.e., the western boreal forest). For example, the mean growing season length at the Refuge (latitude=44 o ) was on average 16–73 d shorter than for sites in the Northwest Territories (latitude=63 o ) and Alaska (latitude=61 o ) recently used to compare intra‐specific initiation dates and clutch size in lesser scaup across North America (Gurney et al 2011). Furthermore, arrival dates for 4 adult female scaup in 2008 that were radio marked in 2007 was 7 May, whereas arrival dates for scaup on the Old Crow, Yukon (latitude=63 o ), was 15 May in 1960.…”

Relative contribution of lipid sources to eggs of lesser scaup

“…The high elevation wetland has a short growing season comparable to northerly breeding areas where the majority of scaup breed (i.e. the Western Boreal Forest; Gurney et al 2011).…”

Full Issue

“…We also delineated wintering ground origins for 2 populations of breeding scoters: Redberry Lake (studied during [2002][2003][2004] in southwest Saskatchewan (52. 668N, 107.178W;Kehoe 1989) and at Cardinal Lake (studied during 2002-2006) in the Northwest Territories, southeast of Inuvik (67.618N, 133.668W; Gurney et al 2011; Figure 1; Table 2). …”

“…Predictor variables in models of clutch size were the same as for timing of breeding but also included clutch initiation date to account for seasonal declines in clutch size, a pattern observed consistently in singlebrooded birds (Krapu et al 2004, Gurney et al 2011. To assess whether effects of clutch initiation date and winter origin on clutch size were confounded (because Atlantic birds tended to nest later), we also ran a clutch size model that included winter origin but not clutch initiation date.…”