Tuesday, September 2, 2008

how many broods for Wisconsin songbird species?

While doing a set of early fall/late summer bird surveys these past few weeks, I was struck by the number of species of passerine birds that were/are still on territory(or at least still singing) as of this date. This made me wonder how many Wisconsin passerines have multiple broods, and are still engaged in that aspect of their annual cycle in late August or even early September. Using the Breeding Bird Atlas and a variety of other references, I tracked down the following information:

1) A fair number of WI passerine bird species have multiple broods.
2) A good percentage of Neotropical migrants that breed in WI have only one brood (not surprising given their brief stay in WI each summer), but some do have more than one.
3) Some permanent resident species have only one brood, even though they do not need to leave on migration.
4) There is still a need for more research on this aspect of some species’ annual cycle; in other words, we simply don’t know for certain how many broods are raised by some species.

I am finding some Eastern Wood-Pewees and Red-eyed Vireos still singing this week and many more last week. What's going on? These two species both probably have only one brood, (but this is not certain for the pewee). Why would males still be singing now if they had completed their nesting cycle? I have not yet found an answer to this in the literature.

Utilizing this as a framework for questions, I developed a set of lists (not exhaustive lists, to be sure) for some relatively common species, with this information. There's a lot more to learn.

One brood

Willow Flycatcher
Least Flycatcher
Great Crested Flycatcher
Eastern Kingbird
Warbling Vireo
Purple Martin
Red-eyed Vireo
American Crow
Bank Swallow
Cliff Swallow
N. Rough-winged Swallow
Black-capped Chickadee
White-breasted Nuthatch
Blue-gray Gnatcatcher
Chestnut-s. Warbler
Yellow Warbler
Black-throated Green Warbler
Cerulean Warbler
Black-and-white Warbler
Blackburnian Warbler
American Redstart
Mourning Warbler (probable)
Scarlet Tanager

Multiple broods (number)

Eastern Phoebe 2
Barn Swallow 2
House Wren 2
Sedge Wren 2
Marsh Wren 2
Eastern Bluebird 2
Wood Thrush 3
American Robin 2
Gray Catbird 2
Brown Thrasher 2
Cedar Waxwing 1-2
Common Yellowthroat 2
Field Sparrow 2
Chipping Sparrow 2
Eastern Towhee 2
Grasshopper Sparrow 2
Henslow’s Sparrow 2
Vesper Sparrow 2
Savannah Sparrow 2
Song Sparrow 2
Swamp Sparrow 2
Clay-colored Sparrow 2
White-throated Sparrow 1-2
Northern Cardinal 2-3
Rose-breasted Grosbeak 1-2
Indigo Bunting 2
Red-winged Blackbird 2-3
Eastern Meadowlark 2
Western Meadowlark 2
Common Grackle 1-2
American Goldfinch 1; occ 2

Number of broods is unknown or uncertain

Eastern Wood-Pewee
Acadian Flycatcher
Cedar Waxwing
Veery (probably 1, but?)
Yellow-rumped Warbler
Northern Waterthrush

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