Moulting makes birds tough to identify
When thinking of a particular bird species, most new birders likely visualize the adult male in breeding plumage. These often bright colours are what draw many of us to birds in the first place. Most birds go through at least one moult per year however. This replacement of feathers freshens up plumage and gives many birds a different look.
Because of this, moults also present advanced birders with endless identification challenges.
The moulting process is energy-intensive so plumage for many species is replaced after nesting season and before the southern migration. Many birds replace their bright feathers with an often drab look that is known as basic plumage. This is most noticeable in male birds.
For small birds, an annual moult has just happened. Chickadees, swallows, woodpeckers, vireos, and flycatchers are among those that moult once each year in late summer.
Birds including warblers, tanagers, and buntings moult their feathers now but they also have a partial moult before the next breeding season.
This is why many warbler species in their so-called basic plumage are difficult to identify. By the time they return in the spring however the colours and other field marks are completely distinctive.
The blackpoll is utterly transformed, for example. Its basic plumage that is seen now is a drab green. The breeding plumage is a bold black and white look.
A few of our birds such as marsh wren and bobolink go through two complete molts each year. Like a blackpoll warbler, the adult male bobolink has a completely different look in spring and fall.
Since many of the feathers of our larger birds including eagles, vultures, and gulls are so big, their moults occur over the course of years.
This allows us to age bald eagles that are between one and five years. Gulls’ moults represent perhaps the greatest identification challenge.
Many duck species have distinctive breeding plumages. This is particularly true of drakes. Ducks moult in late summer and both the males and females of most duck species will appear brown. This is referred to as eclipse plumage. While the birds’ primary feathers are being replaced, they can’t fly for a short period.
During this so-called eclipse phase, bird watchers will key in on other details such as bill colour and shape to help get to a species iden- tification.
In 1959 Philip Humphrey and Ken Parkes introduced a system and lexicon meant to assist in the study of moulting. Published as An Approach to the Study of Molts and Plumages, the Humphrey-Parkes system has stood the test of time.
Several interesting books have since been written on the subject. My go-to volume is Molt in North American Birds, a Peterson Reference Guide written by Steve Howell.
Nature notes
• Last weekend, Hawk Cliff hawk watch co-ordinator Dave Brown and Bob Johnstone, an official raptor counter and president of the St. Thomas Field Naturalists, commented on the relatively low broad-winged hawk numbers. For the third year in a row, the count of these buteos migrating through Hawk Cliff is down. For daily sightings search on “Hawk Cliff by the numbers.”
• Saturday and Sunday are the final two days of the Hawk Cliff Weekend. Events are organized by Thames Talbot Land Trust, St. Thomas Field Naturalists, and Monarch Watch. Events start at 11 each day. Visit thamestalbotlandtrust.ca for details.
• Swift Care Ontario is a Komokabased registered nonprofit organization that has for many years focused on the rehabilitation of chimney swifts and other bird species at risk in Ontario. The 2017 rehab season wrapped earlier this month with the successful release of rescued hatchlings at the Labatt’s Brewery chimney near downtown London. I learned from Swift Care’s co-directors Carolyn Denstedt and Debbie Lefebre that because of Swift Care’s national reputation, this season’s rehab and release included swifts from outside of the province. For more information about Swift Care, go to their Facebook page.
• Forest City Image Centre hosts a nature photography day at Circle R Ranch in Delaware on Sunday, Oct. 1. This will be an opportunity to chat with industry experts and try new equipment. Birds of prey will be on hand. Tickets are $15 and must be purchased in advance. For details visit http://www.semhq. net/naturephotographyday/. g.paul.nicholson@gmail.com