Warning: Migrants Ahead!

By Nick Anich August 1, 2016
Cape May Warbler Setophaga tigrina

As we move into August, it’s a great time to confirm birds using the FL (Recently Fledged Young), CF (Carrying Food), and FY (Feeding Young) codes.

BUT – remember back in April and May when we had to think hard about which birds were breeders versus which birds were migrants? We are about to leave the glorious months of June and July (where you could assume the majority of birds you encountered were at least possible breeders) and head back into migration season.

Shorebirds have been migrating south for a month now, and recently we have begun to see songbirds trickle back in to the state. Moreover, some species that nest within Wisconsin are undergoing post-breeding or juvenile dispersal movements, meaning they are moving around a lot even if not truly migrating yet. Here are a few things to remember for the weeks ahead:

1. Not every bird defaults to H or S anymore. Did you just pick up 3 new species of warbler for your block at the end of July? Be careful! Two processes can result in birds moving around now: one is real migration, birds that are coming to us from Canada, but the other is post-breeding dispersal. Some bird species (think herons, terns, and gulls) are notorious for dispersing in unexpected directions, even north, after breeding. Waterfowl may move to more productive marshes. Even songbirds may move to more productive areas for feeding.

2. Be careful with FL. Late summer migration and dispersal movements can include both adults and young-of-year birds. Just because a bird is in juvenile or immature plumage doesn’t mean it was hatched in your block. The best cue to look for is the tail, which in recently fledged young is typically shorter than that of adults. Short, awkward flights or small groups of closely-associating young birds may be additional signs they were produced locally.

American Redstarts. Photo by Ryan Brady.

American Redstarts. Photo by Ryan Brady.

3. If mom and dad are stuffing food in baby’s mouth, you are probably safe. Although family groups may well wander hundreds of yards from where the nest was, if the young are still dependent on the parents for food, it’s a good assumption that they all just didn’t fly in from Canada. (Some exceptions do apply, perhaps the most notorious being Caspian Terns.)

4. Consult (and help us refine) the Breeding Guideline Bar Chart. You may remember this chart serves as general guidance for when to assume a species is breeding (B), when a species is likely in migration (M), and when we are in the transition period with Either (E) possible. Many species move from B to E in the month of August, so you should be aware and asking yourself if you’re finding the species in a place where you’ve had it before, in suitable habitat, or if you might be dealing with a migrant. See our spring writeup about the bar chart here. Don’t forget that your observations take precedence over the bar chart — if you see a bird feeding young but the chart says migration, don’t hesitate to mark it down as feeding young! Because this is our first field season, we aren’t sure how well the chart will perform during this fall transition phase and expect to revise it — with your help — in the offseason. The Breeding Guideline Bar Chart is available here as a simple .pdf and a sortable spreadsheet. There is a quick link to the .pdf version on the top right side of the Atlas eBird front page.

5. Some birds are late breeders. Birds like Cedar Waxwing and American Goldfinch get started relatively late. Grouse, Wild Turkey, and N. Bobwhite can be found with young broods into August. Rock Pigeon can be found breeding into November! And a few pairs of nearly any species could even nest late into summer if they lost earlier nests for some reason. So there are certainly birds to be found and confirmed, you’ll just have to do so with additional awareness.

American Goldfinch. Photo by Nick Anich.

American Goldfinch. Photo by Nick Anich.

The Atlas season definitely isn’t over yet, we just have to be more aware and cautious going forward as to whether the adults and young you encounter really came from your block, or might be wandering in from elsewhere. When in doubt, please add comments about the situation to your eBird report and consult your County Coordinator, Atlas staff, or fellow atlasers via the many communication channels available from our website at www.wsobirds.org/atlas.