Signs of spring—leaf-out, flowering, insect emergence, and bird migration—are happening increasingly early, and are among the most dramatic changes that have occurred with a warming climate. These earlier shifts in phenology (the timing of seasonal biological events) are one way in which plants and animals are responding and coping with climate change. In years with warmer springs for example, birds may advance the timing of when they breed to coincide with earlier vegetation green-up and peak prey abundance, and this match in timing ensures successful reproduction and survival.
While some species and populations are keeping pace with warmer springs by breeding earlier, others have not changed their timing, and are even breeding later than they have in the past. These inadequate shifts in breeding phenology can pose an increased risk of ‘phenological mismatch’ with prey that has been shifting at a faster rate, a phenomenon which has been linked to population declines in many bird species. Migratory birds are thought to be particularly vulnerable to mismatch, as their journeys place them thousands of kilometers away from changing conditions on the breeding grounds, and limit the time available to breed earlier in the year.
Figure 1. Diagram representing the full annual cycle of a migratory American Kestrel. Migrants must breed, molt, and migrate to spend the winter in areas that are distant from the breeding grounds. A migrant’s annual cycle is relatively complex compared to that of a resident kestrel that remains at the breeding grounds year-round. These additional stages may place constraints on the ability of migrants to adjust their timing during the breeding season, which could increase the risk for phenological mismatch.
Why and how some species and populations are able to shift their timing in response to climate change remains poorly understood, but is critical for predicting how species, communities, and the ecosystem services they provide will change in the future. To understand how factors associated with climate change and migration strategies (from long- and short-distance migrants to residents) affect American Kestrel phenology, the Full Cycle Phenology Project and its partners are collecting range-wide data on timing during each stage of the annual cycle. This allows us to sample populations that exhibit dramatic variation in both their migration strategies and the timing of annual cycle events such as breeding and migration.
We established study sites at 13 US Department of Defense (DoD) military installations, with approximately 20 kestrel nest boxes per site. With the use of time-lapse camera imagery and in-person monitoring provided by DoD biologists, we are banding adult and nestling kestrels, collecting feather samples for DNA analyses, and measuring breeding phenology (date of nest initiation) across these different kestrel populations.
Figure 2. US Department of Defense study sites (purple polygons) established in 2017 and 2018 to monitor American Kestrel nesting phenology, nest success, and survival.
In addition to our DoD nesting data, we are leveraging nest monitoring records from citizen-scientists through the American Kestrel Partnership and Cornell Lab of Ornithology’s NestWatch Program. As a result, we are assembling a comprehensive dataset to better understand how kestrel breeding phenology varies (and what factors drive this variation) at a continental-scale.
For the first time, we are deploying state-of-the-art GPS-Argos satellite transmitters on kestrels on their breeding and wintering grounds to estimate their migration departure and arrival dates, distance, speed, and connectivity in each major flyway. These devices, along with body measurements and feather samples will allow us to understand how individual condition, genetics, and climate experienced at each stage of the annual cycle influences the timing of the migratory period (and in turn, breeding phenology).
Figure 3. A breeding female American Kestrel fitted with a 3.5 g Lotek GPS-Argos satellite transmitter near Manning, Alberta in June 2018 (left). Fall migratory locations and route (red circles and dashed line) of the same individual as of 12 October 2018 (right).
Ultimately, we hope to gain a better understanding of how phenology across the annual cycle is related to climate and other factors. With this information, we can begin to develop better predictive models with the goal of reliably forecasting the responses of kestrels and other migratory landbirds to climate change.
Read about our work on Consequences of the Timing of Breeding in American Kestrels
Text by Jay Winiarski (PhD Ecology, Evolution, and Behavior student).
Project: Environmental drivers of timing of annual cycles of migratory birds.
email jasonwiniarski at u.boisestate.edu