For many locals we are in the thick of summer, but for us at the Lesser Slave Lake Bird Observatory and our songbirds, it is already fall as most of our local birds have finished breeding and southward migration is well underway.
Overhead we are seeing a steady trickle of warblers, sparrows, and blackbirds with the odd finch, shorebird, or hawk. Yet very little has been captured as a bear encounters, a habituated fox, and bad weather have conspired to keep the nets closed to keep birds safe. Similar to last week, much of the activity is thanks to migrating Myrtle Warblers and Tennessee Warblers.
Above: This juvenile Tennessee Warbler was caught recently already migrating south.
Last week’s articles featured Myrtles, so this week let’s highlight Tennessee Warblers. Tennessses hatched nearby just months ago are already on their long journey to Central and South America while their parents hang around replacing all their feathers. In fall, this species is fairly unremarkable and overall olive-green with white underparts to join the ranks of confusing fall warblers. They can be distinguished by their unmarked short, square tails, white undertail coverts, and thin eyelines.
Most of our warbler species exhibit high site fidelity meaning they will return to the same place to nest year after year. But not Tennessee Warblers. They are nomadic and it is very uncommon for us to recapture a Tennessee Warbler we’ve banded in previous years. Similarly, their populations ebb and flow following spruce budworm outbreaks and can see extreme highs and lows. With 59 captured so far this fall, we may be entering another population peak in coming years. We’re a little concerned since the last Tennessee Warbler peak in 2021 banded 1,174 birds and almost used all the bands of the size we use for Tennessees before replacements could arrive from Ottawa.
Another well-researched spruce budworm specialist is Bay-breasted Warblers. They are also an overall olive warbler in the fall, but with white tail spots and two white wingbars. We have been surprised this year that this species has also been found frequently breeding in our monitoring sites with at least five breeding pairs detected where normally we don’t find a single one. At least one of these pairs successfully fledged young.
Above: This female Bay-breasted Warbler was half of a pair that successfully fledged young in our MAPS site RESI.
A recent study suggests that Bay-breasted Warbler detections can be used as an early indicator of spruce budworm infestations, so we are waiting to see if our spruces will soon be crawling with these caterpillars.
It seems that when we have a big year for Tennessee Warblers, our eastern counterparts will have a big year for Bay-breasted Warblers. Perhaps this year we will see high counts from both species!
To see our monitoring program for yourself, join our public Bird Observatory Tours every Wednesday and Saturday from 9 to 11 AM until the end of August (weather and wildlife permitting). For more information, please call the Boreal Centre at 780-849-8240.
By Robyn Perkins, LSLBO Bander-in-Charge
