Breeding Bird Survey
Larry Cartwright Marks 20 Years at Breeding Bird Survey
Breeding Bird Survey, 2015
Forty volunteers participated in the annual Dyke Marsh Breeding Bird Survey from May 30 to July 4, 2015, adding the part of the marsh west of the George Washington Memorial Parkway to the survey for the first time. FODMers documented 48 species as confirmed breeders, which Larry Cartwright, Survey Coordinator, believes is a new survey record.
Least bitterns (Ixobrychus exilis) appear to have one of the best breeding seasons ever, reported Larry, with a nest or fledged young documented from at least three locations. Most species of woodland songbirds experienced higher than normal nest failures at the beginning of the breeding season, but seemed to have greater success with second or even third clutches beginning in mid-June. At least two, species stood out because of their reduced presence: northern parula (Setophaga americana) and Baltimore oriole (Icterus galbula). Ospreys (Pandion haliaetus) did extremely well with most nests producing young.
Especially disappointing was the surveyors' observation that the breeding population of marsh wrens (Cistothorus palustris) may have finally crashed. Teams found only two vocalizing males and they were not identified until late June, well after spring migration concluded. They likely were relocated failed breeders and did not establish territories at Dyke Marsh, as far as we know. See Marsh Wren - Loss of Habitat, Loss of Birds for more information on the marsh wren.
Breeding Bird Survey Results
The 2015 Dyke Marsh Breeding Bird Survey was conducted between Saturday, May 23 and Sunday, July 5, but any data collected outside of this period that confirmed a breeding species was entered into the database. This permitted us to weed out most migrants that do not use the marsh to breed. I also included information provided from the Sunday morning walks and reliable individuals. In previous years, the survey tract encompassed the Belle Haven picnic area, the marina, the open marsh, the Potomac River from the shoreline to the channel, and the surrounding woodland from the mouth of Hunting Creek to south of Morningside Lane. In 2015 we added the West Marsh to the survey tract. The West Marsh is defined as that portion of the Big Gut and the surrounding woodland that lies west of the George Washington Memorial Parkway up to River Towers.
The Dyke Marsh Breeding Bird Survey is undertaken as part of a continuing biological inventory of the tidal wetlands. The breeding status of each species is determined by means of behavioral criteria. Species are placed into one of four categories: confirmed breeder, probable breeder, possible breeder, and present. Volunteer observers participating in the 2015 survey reported 84 species at Dyke Marsh between May 23 and July 5. The 2015 list contains 48 confirmed breeding species, four probable breeders, and 13 possible breeders. An additional 19 species were present, but either were not in suitable breeding habitat, were colonial breeding waterbird species not using a rookery inside the survey tract, or out of range.
There was a void in the marsh during the 2015 breeding season, a profound absence in the Narrowleaf Cattails that have supported the nests of Marsh Wrens for so many years. The Dyke Marsh breeding population of Marsh Wrens failed to arrive in 2015. Canoe teams reported two calling Marsh Wrens on the large island north of the Haul Road peninsula for the first time only in early July, but at that late date, I believe that these birds were possibly relocated failed breeders from another population. Whatever the case, Marsh Wrens dropped from their normal status as Dyke Marsh confirmed breeders to merely possible breeders in 2015.
The failure of Marsh Wrens in 2015 to arrive and occupy the marsh during spring migration in May was hardly unexpected. In her study of Marsh Wrens at Dyke Marsh in 1998 and 1999 as part of her Master’s Thesis, Population Abundance and Habitat Requirements of the Marsh Wren (Cistothorus palustris) at Dyke Marsh Wildlife Preserve: An Urban Conservation Challenge, Sandy Spencer found slightly less than three dozen territorial males at Dyke Marsh. Sandy pointed out that Marsh Wrens were once abundant along the Potomac River close to Washington DC, but were experiencing declines by the 1960s. Habitat loss was the overriding cause, but Sandy also saw additional problems with the Dyke Marsh breeding population, including high rates of nest predation, and narrow preferences for nesting territories. She speculated that this could put the Marsh Wren breeding population at risk over the long term.
Sandy’s concern was warranted. Soon after her study, the number of territorial or singing males dropped from less than three dozen to around 18. The decline was more immediately noticed in the Big Gut portion of the south marsh. The birds disappeared from the Big Gut for several years and then briefly returned between 2011 and 2013, with an active nest documented in 2013. Then in 2014, there were no Marsh Wrens to be found anywhere in the Big Gut.
The Marsh Wren population in the north marsh was centered around the Narrowleaf Cattails to the north of the Haul Road peninsula and the largest of the adjacent islands. After 2000, the number of singing male Marsh Wrens in the north marsh fluctuated from an estimated low of eight to a high of perhaps 16. In 2015, we had absolutely nothing except the late arriving males. The unfortunate loss of Marsh Wrens at Dyke Marsh may be a result of an overall regional decline exacerbated by conditions unique to Dyke Marsh, based on Sandy’s thesis and conversations with local experts and experienced birders. We hope that the absence of Marsh Wrens will be temporary as we prepare for marsh restoration, but know that there are no guarantees.
In contrast to the sad tale of Marsh Wrens, Least Bitterns appeared to have a decent breeding season. During the 2015 survey, Least Bitterns were concentrated in the tributaries of the Little Gut and the channel that separates the Haul Road peninsula from the largest island to the north. Volunteers reported smaller numbers of Least Bitterns at the end of the peninsula just east of the boardwalk, on the north side of the large island, and in the inlet adjacent to the north side of the dogleg. Numbers appeared to be slightly reduced in the Big Gut, but the birds were not impossible to find. It may be that Least Bitterns are gradually withdrawing from the southern half of the Big Gut, possibly as erosion accelerates, and concentrating in the northern half. That, however, is still speculation on my part and bears a close look during the 2016 survey.
Least Bittern youngsters were found, not surprisingly, in areas of their heaviest concentration during the 2015 survey. In late July, I received reports of a fledged Least Bittern and then a family group in the channel separating the Haul Road peninsula from the adjacent island followed a few days later by additional reports of a Least Bittern fledgling attempting to fish in the Little Gut. Admittedly, we conducted more Least Bittern dedicated surveys after Independence Day then we have in the past, but the effort produced positive results. Even during the regular survey, we found more breeding pairs in the marsh, including a pair copulating in one of the Little Gut tributaries, than I can remember in previous years.
I want to add that this does not mean that the Least Bittern will not meet the same fate as the Marsh Wren. One explanation might be that the birds are becoming more concentrated in remaining suitable habitat around the Haul Road peninsula as the marsh erodes in the south, and thus temporarily easier to find at these locations. However, crowded conditions may not be conducive to long term overall breeding success, and provides another reason to keep an eye on these birds in 2016.
Most of our Dyke Marsh raptors had a successful breeding year in 2015. The Morningside Bald Eagle nest was abandoned by January, 2015, but the new nest south of Tulane Drive fledged one healthy youngster by the first week in June. Ospreys constructed a total of 11 nests in the survey tract. Two of these nests were abandoned, but the breeding pair in both cases constructed new nests at different locations. Of the nine active nests, eight fledged youngsters. The highly visible and popular breeding pair at the marina nest saw its three nestlings take their first, but truncated flights, on July 1. One of the breeding pair that abandoned its original nest and rebuilt a second one also fledged youngsters, but at the end of July. Better late than never it seems!
As far as nocturnal raptors are concerned, we hoped to confirm our Eastern Screech-Owl pair as Dyke Marsh breeders. Volunteers documented the pair together, and witnessed copulation, but we could not confirm breeding. That has been the case for several years now. We were in for quite a surprise, however. On April 12, several of us spotted a pair of Barred Owls in a tree in the wooded spot between Marina Road and the south picnic area. One of the birds was raising and lowering its head as if feeding nestlings, but we could not be sure. At least one of the owls was spotted twice after that and then on May 5, I saw the Barred Owl breeding pair near the Haul Road entrance accompanied by a fledged youngster. The Barred Owl family group was perched less than 30 feet from the traditional primary roost cavity of the Eastern Screech-Owls. That’s potentially bad news for an Eastern Screech-Owl because a Barred Owl can easily make a meal out of a smaller owl.
As far as our Dyke Marsh songbirds fared, Eastern Kingbirds, Warbling Vireos, and Orchard Orioles were present in expected decent numbers, and all were confirmed as breeders by the documentation of multiple nests or numerous fledged young and family groups for each species. In one instance, a Warbling Vireo pair in the north picnic area had difficulty with Eastern Kingbird neighbors as the vireos unsuccessfully attempted to prevent the kingbirds from demolishing their nest.Although not as numerous as Eastern Kingbirds, Warbling Vireos, and Orchard Orioles, Eastern Wood-Pewees and Red-eyed Vireos also fledged nestlings, although in one case the youngster being fed by a Red-eyed Vireo parent was a Brown-headed Cowbird. American Crows bred at Dyke Marsh for the first time since 2003 when West Nile Virus swept through the area. Fish Crows have dominated the breeding scene at Dyke Marsh since then, but it appears that American Crows are working their way back into the picture.
Baltimore Orioles and Prothonotary Warblers were tallied in the confirmed breeder category, but neither species seemed as numerous as in previous breeding seasons. In addition, Northern Parulas, not confirmed as 2015 breeders, seemed to be singing from fewer locations than last year. Maybe this is a result of normal yearly fluctuation in population size, but in the case of Prothonotary Warblers, the seemingly lower numbers may be a result of snags falling over at a faster rate, depriving perhaps some birds of an adequate choice of nest cavities.
Brown-headed Cowbirds appeared to have a banner breeding year at Dyke Marsh in 2015, with Eastern Phoebe, Red-eyed Vireo, Song Sparrow, and Northern Cardinal all recorded as host parent species.
I feel personally indebted to all those who have taken the time and the effort to supply data as part of a survey team or who have led the Sunday morning walks during the survey period. Some of you have volunteered for many years, even going back over two decades when I became the survey’s compiler. Thanks so much to all of you. Those who contributed to the 2015 Breeding Bird Survey in alphabetical order are Dave Boltz, Jennifer Cowser, Ed Eder, Myriam Eder, Sandy Farkas, Kurt Gaskill, Susan Haskew, Gerry Hawkins, Ellen Kabat, Lori Keeler, Elizabeth Ketz-Robinson, Ginny McNair, Larry Meade, Roger Miller, Nick Nichols, Marc Ribaudo, Rich Rieger, Don Robinson, Laura Sebastianelli, Robert Smith, Ned Stone, Jessie Strother, Sherman Suter, John Symington, Meg Symington, Russell Taylor, Brett Wohler, Margaret Wohler and Katherine Wychulis.
The 2015 Breeding Bird Survey Results:
Confirmed - 48 Species: Canada Goose, Wood Duck, Mallard, Least Bittern, Osprey, Bald Eagle, Mourning Dove, Barred Owl, Red-bellied Woodpecker, Downy Woodpecker, Hairy Woodpecker, Northern Flicker, Eastern Wood-Pewee, Eastern Phoebe, Great Crested Flycatcher, Eastern Kingbird, Warbling Vireo, Red-eyed Vireo, Blue Jay, American Crow, Fish Crow, Northern Rough-winged Swallow, Purple Martin, Tree Swallow, Barn Swallow, Carolina Chickadee, Tufted Titmouse, White-breasted Nuthatch, House Wren, Carolina Wren, Blue-gray Gnatcatcher, American Robin, Gray Catbird, European Starling, Cedar Waxwing, Prothonotary Warbler, Yellow Warbler, Song Sparrow, Northern Cardinal, Indigo Bunting, Red-winged Blackbird, Common Grackle, Brown-headed Cowbird, Orchard Oriole, Baltimore Oriole, House Finch, American Goldfinch, House Sparrow.
Probable - 4 Species: Eastern Screech-Owl, Acadian Flycatcher, Common Yellowthroat, Northern Parula.
Possible - 13 Species: Green Heron, Black-crowned Night-Heron, Red-tailed Hawk, Spotted Sandpiper, Yellow-billed Cuckoo, Chimney Swift, Ruby-throated Hummingbird, Belted Kingfisher, Marsh Wren, Eastern Bluebird, Northern Mockingbird, American Redstart, Scarlet Tanager.
Present - 19 Species: Lesser Scaup, Double-crested Cormorant, Great Blue Heron, Great Egret, Black Vulture, Turkey Vulture, Greater Yellowlegs, Whimbrel, Semipalmated Sandpiper, Bonaparte’s Gull, Laughing Gull, Ring-billed Gull, Herring Gull, Caspian Tern, Rock Pigeon, Gray-cheeked Thrush, Northern Waterthrush, Magnolia Warbler, Blackpoll Warbler.
Definition of Categories:
Confirmed Breeder: Any species for which there is at minimum evidence of a nest. A species need not successfully fledge young to be placed in the confirmed category.
Probable Breeder: Any species engaged in pre-nesting activity, such as a male on territory, courtship behavior, or even the presence of a pair, but for which there is no evidence of a nest. Since birds can and do sing and display to females during migration, this category cannot be used until the safe dates are reached.
Possible Breeder: Any species, male or female, observed in suitable habitat, but giving no hard evidence of breeding. Unless actively breeding, all birds in suitable habitat before the start of the safe date are placed in this category.
Present: Any species observed that is not in suitable habitat or out of its breeding range.
Definition of Safe Dates: We use safe dates as a means of deciding if a bird can be considered a breeder or a migrant. Safe dates are simply defined as a period of time beginning when all members of a given species have ceased to migrate in the spring and ending when they begin to migrate in the fall. Unless a bird is engaged in behavior that confirms breeding, it will be placed no higher than in the possible breeder category if it is observed outside the safe dates assigned to that species.
Dyke Marsh Breeding Bird Survey Coordinator