By David Hawke -- If you were to chart the highs and lows of excitement for birdwatchers you would see a high peak in late March when the waterfowl migrate northwards, the ducks, geese and swans following the edge of melting ice as the lakes open up.
Then there is a quieter time as the nearby migrants return from the Carolina area of United States.
The next big hurrah happens now, as a group of small and very colourful birds, known collectively as warblers, finally arrive from their wintering grounds in the Caribbean islands and South America.
Just as the ducks follow the receding ice, the warblers follow the bursting open of the tree flowers. As maples, poplars, willows, birch and elm begin their reproduction cycle with a presentation of pollen-rich blossoms, insects of all kinds are attracted by their sweet inviting nectar. As warblers eat only insects, they have to wait for the seasonal event to kick in as they make their way northwards to their own breeding grounds.
When the spring season is unusually cold as it has been for two springtimes in a row, the warblers delay their migration until the plants can catch up to the weather. In the 1980s, the first and second weekend of May was known as “warbler season” but recently this wave of arrivals has been pushed back to third and fourth weekend.
A few of the warbler species will stay here and begin nest building, while the bulk of them are heading to northern Ontario and the boreal forests. Locally we can find yellowthroat and yellow warblers nesting within in the shrubs of our wetlands, and our woodlots will be the summer home of chestnut-sided, yellow-rumped and golden-winged warblers.
Love those names, eh? As indicated by their monikers, this is a colourful lot and makes for a visual treat when you can see them.
In northern Ontario, where many of these birds nest and raise their young within the black spruce forests, several species of wood warblers live in the exact same habitat, thus vying not only with others of their own ilk, but against other warbler species as well for food and nesting sites. How do they do it, so that one species does not out-compete another? Resource partitioning.
As these birds forage through the forest, each has an area of a tree to cover. The Cape May warblers search for insect food amongst and within the very tops of the spruce trees. Blackpoll warblers search the outer tips of the upper third of the tree. Blackburnian warblers search the interior of the upper tree branches. Chestnut-sided warblers search the outer tips of the branches around the middle of the tree. Yellow-rumped warblers search for food around the base and trunk of the tree. By sharing, or partitioning, the tree into search areas, these five warbler species can each survive by finding enough food within their respective areas or parts of the tree.
The added benefit is that the spruce tree is cleansed of harmful insects. And healthy spruce trees eventually make for lots of lumber, don't you know. It has been interesting to watch the gradual but steady acceptance of the lumber trade to understand the intricate relationships between ‘their’ trees and so many other wildlife species.
As we all struggle to understand what climate change really means, and what effects it is having on the environment, the relationship between the flowering dates of trees, the emergence of insects and the arrival of insect-eating migrants is a revealing task. Birdwatching has gone from an odd hobby of the eccentric to a recognized element of scientific study. So, take a moment and be part of this annual cycle of life.
David’s Notebook: A big "thank you" to the readers who have pledged a support for the Couchiching Conservancy's bio-tally Challenge! The team I am on, the Ivory-billed Woodpeckers, has received an amazing amount of support.
© 2020 David J. Hawke