Weekly Reports

Just the other day I was marveling at the quality of this summer; not just the sun and heat, but the lack of wind. I blame myself for saying it out loud, but the Lesser Slave Lake area seems to have remembered that it likes being windy. The arrival of wind has certainly put a damper on migration and our banding totals over the past week. I know I have said it many times to many people that birds aren’t very active on windy days, but I also know that people are sometimes confused by that. Why birds don’t migrate when there is a headwind makes sense, but I often get asked why birds don’t take advantage of tailwinds to help them migrate faster. To a certain extent they will, but it doesn’t take much for the wind to go from helpful to dangerous. Most migratory songbirds have a cruising speed of about 30 km/hour. Our wind speeds are often 30 gusting to 50. To put it into perspective, it is like you driving down the highway with a tailwind of 100 gusting to 170. Also take into account that birds are extremely light in comparison to their surface area – so it’s like driving a tiny little car with a billboard on its roof through extreme winds. So what do birds do in the wind? Some will definitely continue to migrate, but they will do so slower and deeper in the forest, moving through the treetops in between gusts of wind. Most, however, will use poor weather as an opportunity to rest and feed so that they are ready to give it their all once the weather becomes favourable again. If the wind becomes extremely strong they often simply hunker down near the trunks on branches lower in the trees. This leads into an interesting and related topic. How do birds stay perched in such strong winds? A visitor asked the other day how birds stay so firmly attached to their perches and how they are able to sleep without falling. Birds have very specially designed legs and feet that make keeping their grip an involuntary reflex. They have long thin tendons that run along the backs of their legs attaching the muscles high in their legs all the way down to their toes. When a bird bends its legs the tendons are pulled tight over the outside/backside of their ankle joint and the toes lock onto the perch (the main joint you can see on a bird’s leg is its ankle and the main part of its ‘leg’ is actually congruent with our foot). The toes will stay locked until the bird straightens its leg and relieves the tension on the tendon. Falling asleep actually helps a bird to further tighten its grip because as it relaxes its weight settles onto its legs and causes them to bend even more which adds even more tension to the tendons.