This was the second week of fall migration monitoring for the Lesser Slave Lake Bird Observatory. We are actively observing songbirds as they leave the breeding grounds on an arduous journey with the reward of a warm, insect rich winter spent in southern climes. Despite the slow start to bird movements last week, this week’s nicer weather has allowed songbirds to get on the move.
With more birds migrating and pleasant weather letting us safely open our nets, we have banded plenty of birds. As of July 23, we have banded 459 birds from 30 different species in the fall monitoring program. That’s nearly as many birds banded in the first two weeks of fall migration monitoring as we banded for the entire 2020 spring migration monitoring period (banded 494 birds).
Most of the warbler species that you have been able to find throughout the summer are already rushing south. Tennessee Warblers are leaving in droves. You may recall from a recent article that this species has cyclic population trends. This means that their populations are closely tied to that of their favourite food source, spruce budworms. When there are lots of budworms, Tennessee Warblers can feed lots of young mouths and their population grows. After too many Tennessee Warblers are actively foraging, they eat up all the budworms and with little food left, their population crashes. With few predators, spruce budworms flourish, which in turn provides more food to support more Tennessee Warblers and begins the cycle anew. Since we seem to be in a peak year for this species, it only makes sense that they take the top banded spot with 125 banded so far this season.
Pictured (above): Young Canada Warbler captured while trying to fatten up for the journey south.
Among many other warbler species, we have also been banding plenty of Canada Warblers. Canada Warblers are interesting in that they are often one of the last species to arrive and the first to depart. We did not see our first Canada Warbler this year until May 24, but many of our local Canada Warblers seem to already be gone, having flown all the way from Columbia to spend less than two months on the breeding grounds. In late September to early October they will complete their 7,000 km journey south and arrive in South America.
In addition to fall migration monitoring, we continue to run our program that assesses breeding activity. One of the few species still in the middle stages of breeding is the Cedar Waxwing. Similar to Canada Warblers, Cedar Waxwings arrive late to the breeding grounds. Unlike Canada Warblers who are already heading south, some waxwing females are still sitting on nestlings. Since Cedar Waxwings can be found in southern Alberta during the winter months and they do not have nearly as far to go as Canada Warblers, they can take their time breeding to take advantage of the berries that make up most of their diet. Be sure to leave some berries for the waxwings if you find yourself foraging in the coming weeks.
Pictured (right): Cedar Waxwing. Although captured during the fall migration monitoring program, this bird is still actively trying to raise a nest of chicks and won’t be migrating for some time.
By Robyn Perkins, LSLBO Bander-in-Charge
