“So, what is that, Scott, 75?”
“More like 95, Ed, you missed a few while you were looking for that northern harrier over the marsh!”
The location was Mutton Hunk Fen Natural Area Preserve on the Delmarva Peninsula in Virginia, on an October morning perfect for a long walk with binoculars in hand. It is a wonderful 524-acre conservation area with a diverse range of habitats and a lot of birds during autumn migration. Scott was our professional birding guide for a week-long trip organized by famed travel company Road Scholar (formerly known as Elder Hostel, but no one wants to be called elderly these days!). We were based at a former Navy housing facility on Chincoteague Island next to the Goddard Space Center where NASA launches many of its rockets. The scenic highlights of the trip included the marvelous Chincoteague and Assateague Islands and the vast wetlands around them. Yes, we also enjoyed seeing the famous wild ponies scattered around the area.
The count in question had to do with a chickadee-sized bird you may have seen around Harpswell, at least during spring and autumn migrations. The Yellow-rumped Warbler (Setophaga coronata) is not particularly flashy in comparison to its cousins Blackburnian and Magnolia Warblers, and few of them stop here for breeding purposes. I normally come across them while fly fishing or hiking in areas like Rangeley or Moosehead Lake. During the week in Virginia, however, we encountered the bird known locally as “butterbutt” in the thousands, with some zipping around at every stop on our itinerary regardless of habitat.
I traveled to Chincoteague knowing that I owed Amelia an article for this month’s newsletter and had a couple species in mind for further thought and research. However, the lovely Yellow-rumped Warbler swept away the competition for mind-space in my off hours. Please understand; I was fortunate in seeing a wonderful array of birds during the trip, well over 100 different species, with ten species that were new to my life list including beautiful Forster’s and Caspian Terns, the unique Black Skimmer, and the elusive Tri-colored Heron. Maybe it was simply the vast number of Yellow-rumped Warblers we encountered that turned the tide in its favor, or the fact that it is one of the most reliable warblers for viewing pleasure.
The Merlin app from the Cornell Lab of Ornithology describes the Yellow-rumped Warbler exactly as we encountered the multitudes last week: “in migration and winter, found in any woodland or open shrubby area, including coastal dunes, fields, parks, and residential areas.” As with many other warblers, breeding is generally done in coniferous or mixed forest areas. I enjoy seeing them along Maine’s trout streams, often sitting on an exposed perch such as an alder bush above the water, frequently darting out for a short flight to snatch a tasty insect from the air and returning to their perch. The birds are tolerant of human presence when engaging in this feeding behavior.
During breeding season, the male is mostly black with white highlights on his back and wings, showing a black mask and white throat, with yellow patches on the crown, on either side of the breast and the defining yellow patch on the lower back, at the base of his long tail. There is some streaking on the white breast but the belly is mostly white. In the autumn, some of these black feathers fade to a light brown or tan color. Females are more modestly colored than the males for camouflage, but they also show yellow on the flanks and lower back.
The Yellow-rumped Warblers we see are a sub-species known as Myrtle, while out West you are more likely to see the sub-species known as Audubon. These were formerly classified as unique species but ongoing research and DNA studies led to them being combined in a single species. Audubon birds vary in appearance, with males being darker than the Myrtles, with both sexes showing some yellow on their throats. There are other differences in their eye rings and calls but these can be difficult to distinguish. Apparently, the sub-species sometimes interbreed which would yield hybrids even harder to identify. Scientists have identified additional sub-species in Mexico and Guatemala but we would be unlikely to find them in our neighborhoods.
These lovely birds have an extensive range with breeding taking place from Alaska to the Canadian Maritime regions, mostly north of the US/Canada border other than states like Maine, New Hampshire, Vermont, and New York. Some breeding takes place in upper Michigan, Wisconsin, and Minnesota along with higher elevation locations in the Rocky Mountain states, up to 12,000 feet. Migration takes the warblers to the southern US and Mexico, with many birds flying further south to Central America and Caribbean Islands. With climate change, we can expect to see birds changing their patterns; Scott said that a few birds we saw will over-winter in Virginia if they find good habitat and food supplies.
These birds have a varied diet around the calendar. As with most other warblers, they focus on caterpillars and insects during the breeding and nesting season because of availability and nutrition. During the colder months, this warbler is known to feed regularly on berries from the wax myrtle tree, juniper, bayberry, and poison ivy. Their ability to digest the waxy coating on such berries gives them an advantage over many other birds and supports their habit of staying in more northern locations during winter.
These robust warblers often raise two broods during the season, with four or five creamy white eggs incubated for just under two weeks, mostly by the female. Once the eggs hatch, the growth rate of the hatchlings is amazing with both parents feeding them. The young leave the nest in just 12-13 days and are flying in another 2-3 days. Feeding the young birds mostly falls upon the male since the female is off to build another nest and raise her next crop of offspring.
In a world where songbirds face so many challenges, scientists report that the Yellow-rumped Warblers are generally doing well. While their numbers are falling in some areas where development and farming practices may be limiting their habitat, the birds in our part of the world are expanding their range and numbers. I could not find definitive population estimates but that is partly due to the difficulty of studying birds that prefer more remote sites for breeding at higher elevations. Rated as a species of least concern, it appears that we can look forward to enjoying these beautiful birds for the long haul. Just keep an eye out for that yellow patch as a tiny bird flies away from you, old butterbutt is on the move once again!
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