Red-headed Woodpeckers are facultative migrants, meaning that they leave their breeding grounds during some winters but not during others. In general, facultative migration occurs in populations that experience seasonally fluctuating, but year-round food at breeding sites, but it can occur due to other factors such as weather events. In contrast to facultative migrants, obligate migrants tend to leave breeding sites at the same time, in the same direction, and to the same wintering areas each year. The seasonal movements of facultative migrants are not well understood due to their irregular and often unpredictable occurrence.
Our understanding of the migratory movements of Red-headed Woodpeckers is limited to mostly anecdotal accounts and has focused on variation in food resources (i.e., annual mast production) as the primary factor hypothesized to drive whether individuals or populations leave their breeding sites in autumn. Determining the timing and distance of migratory movements, and sites used by Red-headed Woodpeckers outside of the breeding season are important for understanding their population dynamics, informing annual cycle conservation plans, and identifying the cues that may drive their migration patterns.
Over the last three breeding seasons at Cedar Creek we have marked 50 adult Red-headed Woodpeckers with miniature GPS tags to track autumn and winter movements and to better understand the frequency, timing, routes, and overwintering locations of birds that migrate from Cedar Creek. Prior to marking birds with these GPS tags we programmed GPS tags to record location estimates, once per week during the summer and winter months (May-August, December-February) and once every three days during the months in which we expected migration might occur (September-November, March-April). Each spring we attempt to recapture birds wearing these devices so that we can remove them (which are attached using harnesses made with strong ribbon) and download the stored data that shows where birds spent the non-breeding season.
Until recently, all of the data showed that the birds we recovered devices from spent their winters in and around Cedar Creek. However, in June 2019 we recaptured a female Red-headed Woodpecker that had been marked with a GPS tag in 2018, migrated to southeast Iowa in the fall, and returned to Cedar Creek sometime in 2019. The data from this bird’s device indicates that she left Cedar Creek between September 1–4, 2018 and arrived in southeast Iowa sometime between September 7–10, where she appears to have spent the fall and early winter. During this bird’s journey south, the device recorded a location on September 4 a few miles west of Wyalusing State Park, along the Mississippi River. On September 7, the device recorded a location a few miles outside of Dubuque, IA. Both of these locations appear to be in small, dense forest patches within landscapes dominated by agricultural fields.
Location data from the device indicate that this bird spent the next three months in the southeast corner of Iowa, near the borders of Illinois and Missouri, in a patch of dense forest a few miles from the Mississippi River. Battery life on this device was shorter than expected and it stopped collecting data after December 27, 2018. Presumably this bird spent the remainder of the winter in this area, then returned to Cedar Creek in the spring. While the map shows known locations taken during the bird’s fall migration, the lines connecting these points are not representative of the bird’s path—birds do not fly entirely straight during migration afterall! Based on the proximity of the points to the Mississippi River, it seems likely that the bird traveled along the Mississippi River flyway from Minnestoa to southern Iowa.
Our hope is that over the next two years we are able to recover more GPS tags from Red-headed Woodpeckers that leave Cedar Creek for the winter so that we can learn more about their migration patterns and inform conservation planning throughout the species' range.