Shorter migration distances associated with higher winter temperatures suggest a mechanism for advancing nesting phenology of American kestrels Falco sparverius

Abstract

Global climate change has affected avian migration patterns and nesting phenology. Changes in one phase of a bird's cycle will most likely affect other stages, but few studies focus simultaneously on multiple life‐history events. We used western North American ringing records and Christmas Bird Counts to examine whether changes in migration patterns were concordant with advancing American kestrel Falco sparverius nesting phenology. Consistent with previous findings, male kestrels migrated shorter distances than female kestrels, and kestrels nesting in southern latitudes migrated shorter distances than kestrels nesting in more northern areas. In addition, kestrel migration distance decreased significantly from 1960 to 2009 and was negatively associated with winter minimum temperatures. Christmas Birds Counts from the same time period showed increasing indices of overwintering kestrel abundance in northern states (Washington, Idaho, and Utah), where winter minimum temperatures have increased significantly, and concomitant decreases in southern states (California and Arizona). Finally, changes in nesting phenology of kestrels in southwestern Idaho were best explained by warmer winters, not springs. Warmer winters may decrease energetic demands on migrants by allowing for shorter migration distances, decreasing thermoregulatory costs, or both. Decreased energy demands during winter may allow birds to gain resources necessary for reproduction earlier in the nesting season. Higher winter temperatures that decrease (former) constraints on early nesting may be a particularly important mechanism leading to advancing nesting phenology for species with strong seasonal declines in fecundity or intense early season competition for high‐quality nesting areas.

Local Recruitment and Natal Dispersal Distances of American Kestrels

“…Alternatively, warm winters may be associated with an increased proportion of birds that overwinter in the study area in any particular year. American Kestrels tend to migrate shorter distances in warmer winters (Heath et al 2012). Overwintering kestrels that do not undertake long-range movements may be less likely to nest outside the natal region, and they avoid the risks and energetic costs of migration.…”

“…Winters with high DD were more severe than winters with low DD. In winters with higher DD, birds may experience a higher energetic demand for thermoregulation (Ardia 2002), or they may migrate farther from the breeding area (Visser et al 2009, Heath et al 2012. .…”

Using Banding and Encounter Data to Investigate Movements of Red-Tailed Hawks in the Northeastern United States

“…Other studies have documented changing migratory distance and range shifts in many landbird species worldwide (Doswald et al 2009, Visser et al 2009, Paprocki et al 2014). Both global climate change and land-use change have been suggested as factors influencing changing migratory behavior (Visser et al 2009, Zuckerberg et al 2011, Heath et al 2012). Changes to migration include increased winter residency, shorter migration distances, or both (Visser et al 2009, Goodrich et al 2012, Heath et al 2012.…”

“…Both global climate change and land-use change have been suggested as factors influencing changing migratory behavior (Visser et al 2009, Zuckerberg et al 2011, Heath et al 2012). Changes to migration include increased winter residency, shorter migration distances, or both (Visser et al 2009, Goodrich et al 2012, Heath et al 2012. As avian breeding and wintering distributions shift in response to climate and land-use change, and as migratory behavior changes, it will become increasingly important to use data from multiple seasons of the annual cycle to better understand changes in avian populations (Hitch and Leberg 2007, La Sorte and Thompson 2007, Link and Sauer 2007, Link et al 2008, Visser et al 2009, Zuckerberg et al 2011, Heath et al 2012, Martin et al 2014, Paprocki et al 2014.…”

“…A regionally comprehensive and standardized assessment of migration and wintering data across a range of raptor species could greatly clarify our understanding of raptor population change (Bildstein et al 2008a). Several assessments of individual raptor species have used both migration and wintering data (Farmer and Smith 2009, Heath et al 2012, Bolgiano 2013. These studies set the stage for our continent-wide assessment, which offers an improved approach to account for the variability inherent in CBC data.…”