Are life history events of a northern breeding population of Cooper's Hawks influenced by changing climate?

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.

Riding the storm out: select demographics of a breeding population of Cooper’s hawks (Accipiter cooperii) following a severe spring snowstorm

“…In response to recent and rapid climate change, especially warming spring temperatures, Wisconsin Cooper's hawks in the Great Lakes region have advanced their egglaying on average by about 4-5 days during 1980-2015, concordant with advanced spring phenologies of 55 Wisconsin species of plants and migratory songbirds (Rosenfield et al 2016). Notably, some of these birds, including particularly the ground foraging American robin (Turdus migratorius), are primary prey of this raptor especially during the preincubation period (Bradley et al 1999, Rosenfield et al 2016. It is conceivable that some of these phenological advancements may create a mismatch between the tim-ing of (reduced) availability of prey and optimal brood rearing time for Cooper's hawks with consequential deleterious effects on their production and other demographics (Wellicome et al 2014, Whelan et al 2017.…”

“…This schedule avoided the criterion of 80% fledgling age suggested for other raptor species, an age at which visits could result in premature fledging of some nestlings and/or inaccurate brood counts of Cooper's hawk young (Rosenfield et al 2007). I report average brood counts (± standard error) for successful nests in 2018, which are defined as those in which at least one young reached ≥ 18 days of age (Rosenfield et al 2016). Hatching dates per nest were determined by backdating from estimated nestling ages of the oldest chicks based on plumage development (Rosenfield et al 2016).…”

“…In response to recent and rapid climate change, especially warming spring temperatures, Wisconsin Cooper's hawks in the Great Lakes region have advanced their egglaying on average by about 4-5 days during 1980-2015, concordant with advanced spring phenologies of 55 Wisconsin species of plants and migratory songbirds (Rosenfield et al 2016). Notably, some of these birds, including particularly the ground foraging American robin (Turdus migratorius), are primary prey of this raptor especially during the preincubation period (Bradley et al 1999, Rosenfield et al 2016.…”

“…It is conceivable that some of these phenological advancements may create a mismatch between the tim-ing of (reduced) availability of prey and optimal brood rearing time for Cooper's hawks with consequential deleterious effects on their production and other demographics (Wellicome et al 2014, Whelan et al 2017. However, there have been no adverse effects on the average, relatively high and stable reproductive indices of this population of Cooper's hawks during the 36year period (Rosenfield et al 2016).…”

“…Wisconsin Cooper's hawks are principally ground foraging predators, and snow cover may limit access to grounddwelling prey, which includes songbirds, the mourning dove (Zenaida macroura), and small mammals (especially eastern chipmunks, Tamias striatus). Availability of such prey may trigger egglaying in Wisconsin Cooper's hawks (Rosenfield et al 2016). The intense spring storm in 2018 precluded for the first time in 39 years my travel to my Cooper's hawk study nests because virtually all roads (and landscapes) became impassable with deep, wet snow for four days following the storm in and around Stevens Point, Wisconsin (Fig.…”