Now that the dust from the Spring migration is settling, I get a chance to look through some of the data we’ve collected. I am particularly interested in the retrap data – the chronicle of birds that we’ve banded at a previous time and have recaptured again. Of course, we retrap a lot of the full-time residents – chickadees, woodpeckers, nuthatches – proving that they are indeed residents. But the most fascinating for me are the long-distance migrants that return year after year. Here’s a few that we encountered this Spring:
Orchard Orioles are trans-Gulf (of Mexico) migrants in the Spring. They spend the Winter anywhere from Mexico to northern South America in open forests and edge habitat where flowering trees are found. The flight distance from Ruthven to San Jose, Costa Rica is about 3,700 km. What a flight. This bird has made the return flight 6 times!
Baltimore Orioles also spend their Winters from southern Mexico right down to northern South America spending their time in moist forest and shade coffee plantations.
The Blue-winged Warbler winters in humid evergreen and semideciduous forest and edge habitat from southern Mexico to Costa Rica and, sometimes, right down to Panama or the West Indies. So its flight distance is about the same as that of the orioles – but it weighs only 7.5-8 grams versus their weight of 32-35 grams. So a 9-year old Blue-winged Warbler is a marvel in and of itself.
The thing I would like to stress here is that these birds aren’t returning willy-nilly to just anywhere. When they set out from their wintering ground they have the destination down pat – they are flying to their Summer home: Ruthven Park, where they know the habitat intimately, probably right down to the trees and shrubs present in the territories they would like to carve out and the to food that these habitats contain. It’s not a random thing and these recapture records clearly show that.
But what happens if they return and find that their “home” has been destroyed, doesn’t exist anymore? Chaos. They have to use precious resources (and remember that they have used up most of their energy reserves to get here – returning local residents usually are not carrying any fat) to try to find another suitable habitat to nest in – one that probably already has resident birds which will fight hard to preserve their right to it. There’s a good possibility that the breeding season for these displaced birds will be lost – and maybe the bird itself.
Take a look around. Urban sprawl is exploding in southern Ontario. Binbrook and Caledonia, once two nice rural towns are now small cities (or soon will be) housing the workforce that runs Toronto. Over 3,000 new (large) houses are currently being constructed on the outskirts of Caledonia on the north side of the river and there’s plans for an even larger number on the south side. Agricultural lands are herbicided deserts awaiting planting or vast monocultures. On my walk this morning just outside of the village of York I observed a large field of winter wheat and another awaiting tilling. I never saw a single bird associated with them. I saw a couple of birds flying over, going from one place to another, but never into them to look for food or to return to a nest. For wildlife such fields are wastelands. And, now we are learning that they are insidiously toxic wastelands….for ALL life.
I’d like to be able to point to a simple solution but when all is said and done if humans aren’t willing to curb their propensity to breed then I can’t foresee a positive outcome. And beautiful retrap stories like those above will be a rarity if they happen at all.
But enough gloom (it can sure get you down if you let it). Take a look at this next picture: retrap cards for a Yellow Warbler and an American Goldfinch. Sure, it’s just coincidence. But wouldn’t their connection make for a marvellous children’s story!? The tale of two very different apecies that grow up together, go their separate ways for the Winter but, before going, agree to meet again at Ruthven at a particular time in order to “catch up”.