No this article isn’t about basketball - it’s about birds! Raptors, which include hawks, eagles, falcons, harriers, owls and vultures undertake prolonged and extensive migrations over a protracted period of time. What drives them? Where do they go?
Let’s talk about owls first. Most owls are actually quite sedentary and only move short distances during the migration period, but some like the Snowy Owl undertake longer journeys, which are thousands of kilometers long in search of food. One even made it to Hawaii recently. It is generally the availability of food that drives ‘northern’ owls such as the Snowy and Great Gray southward, but if winter food is plentiful, they will stay on their northern breeding grounds all year.
Other smaller owls, such as the Northern Saw-whet, also migrate but follow very specific patterns, routes and timing, not solely linked to food availability. In fact, these small owls may be fleeing the larger raptors such as Great Horned Owls and Northern Goshawks that will relentlessly hunt them in winter when other food is harder to find.
In the spring, hawks migrate northbound, starting in January and complete their migration as late as early May. Why they undertake such a prolonged migration is puzzling. Wouldn’t they want to get back earlier and claim territories and mates? The ones that migrate latest are the ones that won’t stop here but will continue northward, well beyond our borders. Some will go to the edge of the boreal forest and beyond to nest. And anyone who has traveled there in late spring knows that the boreal forest can be snow covered much later than here.
Since the snow hides the prey they rely on, it makes sense to delay their arrival. The earliest migrants are local nesters, which time their arrival to the availability of food. Throughout the spring season, we see the same pattern repeated, the further north they travel, the later they arrive generally.
Vultures are increasingly becoming a fixture in Ontario. We now have two species that regularly overwinter or migrate through the province. The Black Vulture is a newcomer and its migrational patterns are still being established, but the Turkey Vulture is well known and studied. It begins its migration in late March or early April, and is essentially done by the end of April. Likewise, in the fall, Turkey Vultures start to move out in mid-September but the bulk of the birds migrate throughout October and into early November.
October is also the time we see the peak of Golden Eagle migration. This is another species which nests in the high Arctic and leaves those lands only when the local prey is exhausted. Bald Eagles on the other hand have a protracted migrational cycle that can last for weeks in both the spring and fall. This may be because they nest over a much greater part of the province and eat a wider variety of food. The Golden relies on carrion, hares and ptarmigans for the most part, while the Bald will scavenge fish or hunt ducks and mammalian prey. Falcons move through in September and October, often following migrating dragonflies, which provide a mobile food source for the Merlin and Kestrel.
The Broad-winged hawk is anomalous, for it migrates out enmasse in mid-September with most birds moving past in only a few days. Likewise in the spring it travels in sometimes huge flocks, Greater then 50,000 birds on occasion.
Why does this bird leave so quickly and why does it never linger into winter, unlike all the other hawks? Perhaps it has to do with its food sources. It will eat a variety of critters but insects, reptiles, small mammals, nestling birds and amphibians make up an important part of its diet. So with this restricted type of diet it doesn’t make sense to stay here where food will be hard to find. The Tropics is a much better bet!
So, it appears food and weather are the driving forces as to why raptors go and when raptors migrate. Now is the time these great birds are on the move, so get out and see what you can find!
Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line, at www.avocetnatureservices.com and on LinkedIn and Facebook
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Geoff Carpentier is a published author, ecotour guide and environmental consultant. Visit Geoff on-line, at www.avocetnatureservices.com and on LinkedIn and Facebook.