Weekly Reports

After a slow start, fall migration seems to be picking up out at the Lesser Slave Lake Bird Observatory. Every day we see an increase in the number of songbirds heading south overhead. These birds can be extremely challenging for us to identify. For starters they are high in the sky and little more than bird-shaped specks to the naked eye; then to exasperate identifying them visually, they are moving fairly quickly and not in straight lines – making finding them with binoculars before they are gone tricky. If we are able to get them squarely in our sights, we are presented a brief view of just their undersides, an angle not covered very thoroughly in most guide books. Sometimes these quick-moving bird-shaped silhouettes offer us assistance by making flight calls. A bird species’ flight call, just like its song, is unique to its species. Unfortunately, although I’m sure the birds can tell them apart, to our ears they sound practically identical. They are so similar that researchers who do call monitoring of nighttime migrants generally have to get all the sounds converted into sonograms so they can see the differences. After many years of practice though, we have gotten well-practised at this rapid-fire form of birding. On a good day we are able to positively identify about half of the birds that are passing overhead, the other half we are able to at least identify to a family i.e. unknown warbler, unknown sparrow etc. On a bad day, however, many birds get counted as the dreaded unknown songbird code. Myrtle warblers, black-and-white warblers, Tennessee warblers, ovenbirds and Swainson’s thrush are making up the bulk of the migrants right now. Many of the individuals passing overhead are adults, but the vast majority of the ones that we are catching are juveniles. This isn’t very surprising; juvenile birds are not nearly as strong of flyers as the adults. They don’t have the strength or the experience to fight winds or avoid predatory birds up in the open sky so they tend to fly either through the forest or at least just above it so they can rest if they have to. This puts them in range of our nets. Another reason we are catching so many young birds, is that they actually migrate before the adult birds. Unlike ducks, geese and other large birds, songbirds do not need to be taught where to go by their parents, they are instinctually programmed to know exactly where their wintering grounds are. So without any urging or guidance from their parents, young migrants embark on journeys thousands of kilometers long as soon as they are old enough to fend for themselves, which, for most species, is a scant three to four weeks old.