Where do the Warblers Wander? Migratory Connectivity of Canada Warblers and Connecticut Warblers

This summer, biologists from the University of Alberta and the Smithsonian Migratory Bird Center were back in action in Alberta’s boreal forest. In an effort to find out more about where boreal breeding birds spend the winter, and what routes they take during migration, our crews have been putting tracking devices on a variety of bird species including: Broad-winged hawks, Rusty Blackbirds, Olive-sided Flycatchers, Common Nighthawks, Palm Warblers, Canada Warblers, and Connecticut Warblers as part of the Migratory Connectivity Project.

I have spent the last two years researching Canada Warblers for my M.Sc. thesis, so I jumped at the opportunity to work with the Smithsonian’s Michael Hallworth (post-doctoral fellow) to catch both Canada Warblers and Connecticut Warblers and fit them with light-level geolocators: tracking devices that record ambient light levels which are then used to determine locations. An estimated 85% and 95% of the breeding populations of these species, respectively, occur in Canada, and these neotropical migrants make the long journey to and from South America each year. Canada Warblers are listed as threatened in Canada, so there has been plenty of recent interest in finding out more about the drivers of population declines, and in what part of their range these impacts are occurring. Connecticut Warblers are highly under-studied, and known for secretive behavior during migration, so information on their migration ecology is scarce.  img_3031
Photos: Male Canada Warbler with distinct black necklace (left) and male Connecticut Warbler with full grey hood (right)

We headed out to Lac La Biche, Alberta to begin a whirlwind 10 days of “warblering”. Because both Michael and I had previous experience conducting research on Canada Warblers, and because I had worked on Canada Warblers in this area the previous year, we thought this species would be a good place to start. Using mist-nets, playbacks of male territorial songs and a decoy (“Agro Al” made by Hedwig Lankau) to lure them in, we set out to capture some birds. Within three days we had captured our quota of 15 Canada Warblers, including recapturing two of the males that I had colour-banded in 2015 (pictures here). This means these 10 gram birds had successfully migrated to South America and back, returning to the exact same breeding location in Alberta! We fitted all captured males with geolocators as well as unique identifying coloured leg bands to make them easier to relocate next year if and when they return to their breeding grounds.20160608_111640cawacrop220160608_104720Photos: “Agro Al”, our decoy, checks out a caterpillar while trying to lure in a territorial Canada Warbler (left); Anjolene fits a geolocator on a Canada Warbler using a leg loop harness (centre); This male shows off his geolocator light sensor, which will use ambient light to track his location during migration (right).

With the Canada Warblers taken care of, we set out to catch our second species, the potentially more elusive Connecticut Warbler. With our relatively limited knowledge of this species, we were anticipating a lot more difficulty finding and capturing them. We started our day planning on bushwhacking our way ~1 km to an area where this species had been previously detected. However, seconds after opening the door of our truck, we heard a Connecticut Warbler singing its heart out only 50 metres off of the highway. We hurried over and were able to capture the male fairly quickly and fit him with a geolocator. While we were processing our first bird, we heard another not too far away, and so the trend continued for the next few days, in which we caught our 15 Connecticut Warblers (including two in the same net!).

20160607_113110img_3027cawacrop3Photos: Michael extracts our first Connecticut Warbler from a mist-net (left); This Connecticut Warbler displays his new colour bands, which will be used to identify him next year (center); Michael fits a male Connecticut Warbler with a geolocator using a leg loop harness (right).

With the captures complete for this year, we now wait with anticipation until summer 2017 to recapture our males, collect the geolocators and find out where they’ve been!

-Post by Anjolene Hunt

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