Although goose migration has tapered off, our songbirds arrived in droves after being held up by stormy and snowy weather in southern Alberta last week. The biggest days for migration at the Lesser Slave Lake Bird Observatory were May 9 and 10 with around 2,500 Myrtle Warblers counted each day and diversity shot up with only one day recording fewer than 65 species.
Breeding male Myrtle Warblers have bright yellow ‘wing’ pits and crowns, a thick black mask, and slate gray back. 
Spring females are drabber, but still more gray with a subtle mask than is present during the fall.
Some residents and short-distance migrants, such as Black-capped Chickadees and American Robins, have built their nests and are sitting on eggs. There is a flush of colour overtaking the grays of winter not only among the trees and grass, but among the birds as well. As our long-distance migrants arrive from Central and South America, they bring with them vibrancy to the forest – often thanks to the arrival of our warblers.
While this typically small and vocal category of birds is rather drab with shades of beige in Europe, here warblers are often completely or partially bright yellow. The term “warbler” describes the often complex songs of these little birds and was used as far back as the 1600s. Perhaps these bright colours inspired early North American naturalists to initially categorize several of our warblers as flycatchers who are drab here, but sometimes brilliantly coloured in Europe. Our bright warblers are not closely related to the warblers of the ‘old world’, but are instead in the Parulidae, or “New World Warbler” family.
Male warblers are normally brighter and more colourful than females of the same species in spring. These brilliant colours are used to attract a mate and are sometimes replaced in the fall to increase camouflage over the winter. Myrtle Warblers are a species that follows this rule. Interestingly, however, one of our most striking males, the American Redstart, does not become their distinct black and orange until the fall. Others remain yellow year-round. This includes the Nashville Warbler, one of which was captured this week to become only the third member of this species that we have banded during spring.
Another common difference between males and females is migration timing. In order to establish the best territories, males arrive on the breeding grounds before females. Since they have more experience migrating and are often more fit, older birds will also arrive earlier than those hatched last summer. This phenomenon is called differential migration.
While our observational counts provide excellent estimations of the number of birds moving through our monitoring site, only capturing birds can provide these details about their approximate age and sex. This is why, despite only accounting for 1-5% of the birds we encounter in a year, banding is such an important part of our protocols.
By the time this article is published we will have already completed our Birdathon fundraising run on May 15. However, it is not too late to donate!
By Robyn Perkins, LSLBO Bander-in-Charge
