Warblers at Muskegon Lake Nature Preserve

Although work has prevented me from banding many days at the Muskegon Lake Nature Preserve this fall, and coverage has been less than the long-term average, I have at least been able run the nets more often than during the last two years. Flooding has hindered net placement this season, and rainfall has been heavy this September. Temperatures also have been warmer than normal, and this September has been the second hottest in the last 11 years of banding (marginally surpassed only by last year).

As a result of the odd weather, the species gamut has varied wildly in abundance and timing. Many species have been early, but certain others are running late. Even within guilds, numbers have been inconsistent. For example, Swainson's Thrushes usually outnumber Gray-cheeked Thrushes by about 5 to 1; this year I have caught 17 Swainson's but no Gray-cheeked Thrushes. (A nocturnal count on Sept. 28 outside my house in Norton Shores yielded 37 SWTH to only 2 GCTH!). A high ratio of adults for many species has also been unusual. Overall, numbers have been down this fall, but there have been several surprises.

Thirty-six species of warblers have been recorded from Muskegon County (23 of these have definitely or probably nested here). Fifteen species occur frequently at MLNP in the fall, but due to the lack of mature forest, otherwise common species can be scarce. For instance, I only capture about one Black-and-white Warbler each year, almost always at the end of August or the beginning of September, so three this year were welcome. While the first appeared on September 6, the other two did not show until October 4! The individual pictured here is a first-year male; an adult male would have a darker auricular.

Identifying fall warblers can indeed be challenging, yet some birders wrongly figure that much of this difficulty stems from most species molting into a drabber plumage in autumn. However, of those 36 warbler species, 21 exhibit the exact same plumage as they do in the spring. Another nine do show subtle changes (e.g. Nashville and Palm Warblers). That leaves only six that look substantially different in the fall (e.g. Chestnut-sided and Blackpoll Warblers). The problem actually stems from first-year birds. Within each sex, youngsters are considerably duller than adults, and immature females can be especially subdued.

Among some species, small sizes and canopy niches add to the difficulty. In the case of the Northern Parula (this young male was banded September 30), this situation is extreme. While Nashville Warbler (8.8 grams), Magnolia Warbler (8.6 grams), American Redstart (8.2 grams), and Wilson's Warbler (8.1 grams) are quite small, Northern Parula (averaging only 7.8 grams) is positively tiny. They frequent high canopies in migration, and if they do not sing, they are likely to be missed. Despite a lot of birding time, this was my experience this past spring in Muskegon.

Finally, the bird pictured above (yet another immature male), caught on October 11, represents one of the best captures in the station's history. I had never before banded this species in Michigan (though I have caught many in Pennsylvania and Virginia). Though never common, the species was more numerous and widespread across Michigan several decades ago, but populations have steadily declined. Now rare, breeders are mostly restricted to a few Lake Michigan dunes. Lawrence Walkinshaw noted several individuals from Muskegon County in the 1940's and 1950's, and even found a nest in June 1949 (and continued to find more thru 1956), but more recent records from Muskegon are scant.

The timing of this capture is likewise aberrant. Fall records from Michigan are unusual after mid-September (all of mine have been in August), and even in Virginia only 7 of the 78 birds I banded were in October (with the very latest being October 15). As far as size, this is another tiny warbler. Those Virginia birds averaged only 8.0 grams. Though it had some fat deposits and appeared otherwise healthy, this Prairie Warbler weighed just 7.5 grams.

- Brian Johnson