Abstract
Numerous studies have demonstrated earlier timing of spring migration and egg‐laying in small passerines, but documentation of such responses to recent climate change in the life histories of higher trophic feeding birds such as raptors is relatively scarce. Raptors may be particularly susceptible to possible adverse effects of climate change due to their longer generation turnover times and lower reproductive capacity, which could lead to population declines because of an inability to match reproductive timing with optimal brood rearing conditions. Conversely adaptively favorable outcomes due to the influence of changing climate may occur. In general, birds that seasonally nest earlier typically have higher reproductive output compared to conspecifics that nest later in the season. Given the strong seasonal decline in reproductive output, and the heritability of nesting phenology, it is possible that nesting seasons would (adaptively) advance over time. Recent climate warming may release prior ecological constraints on birds that depend on food availability at the time of egg production, as do various raptors including Cooper's Hawks (Accipiter cooperii). Under this scenario, productivity, especially clutch size, might increase because it is likely that this reproductive demographic may be the most immediate response to the earlier seasonal presence of food resources. We demonstrated a statistically significant shift of about 4–5 days to an earlier timing of egg‐hatching in spring across 36 years during 1980–2015 for a partially migratory population of Cooper's Hawks in Wisconsin, United States, which is consistent with a recent study that showed that Cooper's Hawks had advanced their timing of spring migration during 1979–2012. Both studies occurred in the Great Lakes region, an area that compared to global averages is experiencing earlier and increased warming particularly in the spring in Wisconsin. The nesting period did not lengthen. We suggest that the gradual shift of six consecutive generations of hawks was likely in response to recent climate change or warming. We did not detect any long‐term temporal change in average clutch or brood sizes. However, such indices of reproduction are among the highest known for the species and thus may be at their physio‐ecological maximum for this population. Our study population appears to show resilience to and does not appear to be adversely influenced by the recent rate of changing climate at this time.
Highlights
Much evidence suggests that recent climate change has altered life history events of numerous species of birds (e.g., Brommer, 2004; Jenni & Kery, 2003; Wood & Kellermann, 2015)
Sullivan et al (2016) recently demonstrated phenological shifts to earlier spring migration of several raptor species, including Cooper’s Hawks during 1979–2012 in the Great Lakes region of North America, and they indicated that such shifts were consistent with decadal climatic oscillations and global climate change
Such shifts could likely lead to earlier arrival times at breeding territories, which in turn could lead to earlier breeding schedules, a lengthened nesting period, and possibly increased productivity
Summary
Much evidence suggests that recent climate change has altered life history events of numerous species of birds (e.g., Brommer, 2004; Jenni & Kery, 2003; Wood & Kellermann, 2015). Sullivan et al (2016) recently demonstrated phenological shifts to earlier spring migration of several raptor species, including Cooper’s Hawks during 1979–2012 in the Great Lakes region of North America, and they indicated that such shifts were consistent with decadal climatic oscillations and global climate change Such shifts could likely lead to earlier arrival times at breeding territories, which in turn could lead to earlier breeding schedules, a lengthened nesting period, and possibly increased productivity (perhaps an adaptive response sensu Lehikoinen et al, 2010; Fontaine, Stutzman, & Gannes, 2015). The advanced timing of spring migration of these birds was linked to earlier and higher spring temperatures due to climate change (Bradley et al, 1999) One of these species, the American Robin, is the most commonly detected prey item in spring during the preincubation period at Cooper’s Hawk nest sites on our study areas throughout all study years
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