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Breeding Bird Survey

Larry Cartwright Marks 20 Years at Breeding Bird Survey
The Friends of Dyke Marsh honored Larry Cartwright at the quarterly meeting on May 16, 2012, with a certificate of appreciation for organizing and leading the survey for 20 years. This activity, a continuing biological inventory of the birds of the Dyke Marsh Wildlife Preserve, has provided trend information since the 1960s. The Friends also gave Larry a portrait a prothonotary warbler, Larry's favorite bird. FODM President Glenda Booth presided.  Larry Cartwright

Breeding Bird Survey, 2017

The 2017 Dyke Marsh Breeding Bird Survey was conducted between Saturday, May 27 and Tuesday, July 4, but any data collected outside of this period that confirmed a breeding species was entered into the database. This permitted us to filter out most migrants that do not use the marsh or surrounding habitat to breed. I also included information provided from the Sunday morning walks and reliable individuals to supplement data reported by the survey teams. The survey tract encompasses the Belle Haven picnic area, the marina, the open marsh, that portion of the Big Gut known as West Dyke Marsh that extends from the George Washington Memorial Parkway west to River Towers, the Potomac River from the shoreline to the channel, and the surrounding woodland from the mouth of Hunting Creek to south of Morningside Lane. 

The Dyke Marsh Breeding Bird Survey is undertaken as part of a continuing biological inventory of the tidal wetlands.  Our methodology uses behavioral criteria to determine the breeding status of each species that is recorded in the survey tract.  Species are placed into one of four categories: confirmed breeder, probable breeder, possible breeder, and present.  We found 87 species at Dyke Marsh during 2017. There were 46 confirmed breeding species, 8 probable breeders, and 11 possible breeders.  An additional 14 species were documented as 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.

Marsh WrenA territorial male Marsh Wren in the south marsh. Photo by Ed Eder.Marsh Wrens were last confirmed as Dyke Marsh breeders in 2014 with approximately 16 singing males and fewer than a dozen nests confined to the marsh vegetation north of Haul Road.  Marsh Wrens disappeared from the Big Gut in the south marsh after 2006, but a few birds returned to occupy a tributary of the Big Gut that we unofficially call the Northeast Passage between 2011 and 2013.  They failed to return to the south marsh in 2014.  In 2015 and 2016 no more than three singing males were documented in the marsh surrounding Haul Road.  There was no confirmed nesting and Marsh Wrens dropped to a probable breeder status.   

 The same sparse representation of Marsh Wrens was present around Haul Road during the 2017 survey, but surprisingly two or three males in the south marsh occupied territory in the Northeast Passage after a three-year absence.  During a June 25 survey, a canoe team spotted a Marsh Wren carrying nesting material. A subsequent canoe trip to the Northeast Passage reported three Marsh Wren nests.  Two were apparent dummy nests, built by males to attract females.  However, the third nest contained interior lining characteristic of active nests that are accepted and completed by females.  A territorial male was close to the nest. Based on this information, I determined that this lone nest was active and met the criteria to confirm breeding.

I caution against interpreting this one active nest as potentially leading to a return of a viable Marsh Wren breeding population.  The decline in the fortunes of this species at Dyke Marsh has been an ongoing process for over two decades.  It may be part of a regional decline.   Hopefully the marsh restoration will lead to some stability in the marsh habitat and in the absence of other unforeseen negative influences, the Marsh Wren may establish a presence that we can once again enjoy. 

Least BitternA Least Bittern peers from the marsh vegetation on Dyke Island. Photo by Ed Eder.

The Least Bittern is another species at Dyke Marsh that receives our special attention.  Our survey teams have documented the retreat of Least Bitterns from the southern portion of the Big Gut, apparently because of the accelerated erosion.  The data collected during the 2017 survey suggests that there is a strong presence of Least Bitterns at least in some areas of Dyke Marsh. Three separate surveys conducted on June 25, two by canoe and one by foot, collectively reported nine Least Bitterns.  Five of the birds were in the north marsh, including two breeding pairs in a tributary of the Little Gut along the southern edge of the Haul Road peninsula, and the remaining four were in the upper portion of the Big Gut.  Additional breeding pairs also were identified near the Northeast Passage and close to the boardwalk at the end of the Haul Road peninsula during other June surveys.  Despite these apparent positive signs, we found no Least Bittern nests or fledged young and Least Bittern could only be listed as a probable breeder.  My primary concern is that Least Bitterns are being forced into increasingly smaller areas of acceptable breeding habitat at Dyke Marsh and that these heavier concentrations will have a negative impact on breeding success.  It seems odd to be able to document Least Bittern activity in northern locations of the marsh while the entire southern half of the Big Gut remains devoid of these birds.

An interesting relationship developed between Ospreys and Bald Eagles at Dyke Marsh during the 2017 breeding season.  Volunteers documented ten active Osprey nests in an area extending from Porto Vecchio in the north to Angel Island in Pipeline Bay.  Five of these nests, including the highly visible nest at the marina, produced fledged young while the remaining five failed. Although it is often difficult to determine the cause of nest failure in even large breeding birds like Ospreys, we know that two of the Osprey nesting attempts were disrupted by a pair of Bald Eagles.  The Bald Eagles in question could have been the Tulane Drive breeding pair, whose nest also failed by early April or a confused Bald Eagle duo that started building a nest along Haul Road in June when most eagle nests would be fledging young.

A pair of Bald Eagles was first reported perched beside the Osprey nest on Dyke Island on April 7, effectively blocking repeated attempts by the Osprey breeding pair to access the nest.  The Bald Eagles soon became interested in the Osprey nest on the adjacent Coconut Island and perched beside this nest as well.  With the larger and more dominant eagles controlling the situation on the islands, both Osprey pairs eventually abandoned their breeding efforts.  The Bald Eagles never made any attempts to destroy or use either the Dyke or Coconut Island nests but seemed content in just preventing the Ospreys from using them. 

Bald Eagles did have a successful breeding record in 2017.  The Morningside Lane breeding pair had at least one healthy, active youngster in the nest last seen on June 8.  The bird apparently fledged within the following week.

Dyke Marsh hosts a respectable number of neotropical migrant songbirds during the breeding season, including Great Crested Flycatchers, Eastern Kingbirds, Warbling Vireos, Yellow Warblers, Orchard Orioles, and Baltimore Orioles, that are confirmed as breeders every year.  A walk down Haul Road, especially past the dogleg along the peninsula, will likely reveal all six species to the careful observer.  Sometimes the careful observer turns out to be a female Brown-headed Cowbird.  Although we are delighted to watch these species feed their own youngsters, one observer on July 7 reported a bedraggled female Yellow Warbler feeding two Brown-headed Cowbird fledglings that were bigger and likely outweighed her.

Yellow warblerA female Yellow Warbler feeds a much larger Brown-headed Cowbird fledgling. Photo by Ed Eder.Most songbirds are careful about concealing nests to protect them from predators and brood parasites like Brown-headed Cowbirds that victimized the unfortunate Yellow Warbler.  Eastern Kingbirds sometime don’t concern themselves with such incidentals as nest concealment.  During a June 18 canoe survey into the Big Gut, I was surprised to find a completely exposed Eastern Kingbird nest with nestlings about 40 feet up in a dead Sycamore.  Another canoe team doing a different route on the same day also reported an exposed Eastern Kingbird nest containing nestlings, this one just four feet off the ground.  Eastern Kingbirds are quite aggressive and perhaps this aggressiveness just might help negate the need for complete caution and total nest concealment.

Several years ago, I noticed a trend for Mallard hens to have delayed single broods or perhaps even multiple broods containing fewer young.  In the 1990s, the norm would be to observe a Mallard hen in April or May with perhaps a half dozen or more recently hatched young in tow.  After 2000, volunteers noticed Mallard hens with as few as two or three recently hatched ducklings much later in the summer.  Volunteers still reported large broods after 2000, but with reduced frequency.  The 2017 breeding season now holds the record for reduced size late broods at Dyke Marsh.  On September 17, several volunteers observed a Mallard hen in the marina in the company of two youngsters no more than one week old.  A review of my records indicates that this is the first September record for breeding Mallards since I became compiler in 1994.

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.  Orchard OrioleFledged Orchard Oriole young with mother perched above them. Photo by Ed Eder.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.

I have not satisfactorily determined the cause for this trend toward delayed reduced size broods in Mallards. I have speculated in an earlier report that perhaps small broods were the result of increased predation of young, but significant loss of ducklings in a brood only a few days old seems highly unlikely.  An egg predator would probably consume the whole clutch.  Therefore, I tend to discount predation as a significant cause of small broods.  We often see these small brood young several weeks after hatching and they appear quite healthy, so survival rates may be good in the first months of their lives.  The data also shows that breeding bird survey observers often report the cavity nesting Wood Duck with smaller than normal broods at Dyke Marsh.  There may be explanations here that I have not yet entertained. Research continues.             

Finally, I would like to focus on one species that is never mentioned in my breeding bird survey report.  It’s not a rare species because we see it every year, but we never come close to confirming it as a breeder.  That species is the Chimney Swift.  For over two decades I have watched flocks of Chimney Swifts foraging for flying insects over all areas of the marsh and wooded areas and have pondered where do they breed.  They must breed nearby.  After all, they are here every breeding season.  Yet they never give a hint of breeding at all.  Consequently, I was pleasantly surprised to watch Chimney Swifts engaged in a display flight over the Big Gut Bridge on May 25.  It was a beautiful spectacle to behold.  On a more scientific level, it bumped the species up from possible to probable breeder.  Now the question is where do they breed?  In some Alexandria chimney close to the marsh?  Or in the survey tract?  I will continue to keep a lookout.

The Dyke Marsh Breeding Bird Survey is impossible without the effort and dedication of participating citizen-scientists that conduct the surveys:  Eldon Boes, Glenda Booth, Marla Brin, Ed Eder, Myriam Eder, Renee Grebe, Susan Haskew, Gerry Hawkins, Elizabeth Ketz-Robinson, Dorothy McManus, Ginny McNair, Larry Meade, Roger Miller, Heidi Moyer, Sasha Munters, Nick Nichols, Rich Rieger, Don Robinson, Laura Sebastianelli, Phil Silas, Robert Smith, Karen Snape, Ned Stone, Sherman Suter, Todd Kiraly, Brett Wohler, Marcus Wohler, Margaret Wohler.

The 2017 Breeding Bird Survey Results:

Confirmed - 46 Species: Canada Goose, Wood Duck, Mallard, Mourning Dove, Ruby-throated Hummingbird, Osprey, Bald Eagle, Red-bellied Woodpecker, Downy Woodpecker, Pileated Woodpecker, Eastern Phoebe, Great Crested Flycatcher, Eastern Kingbird, Warbling Vireo, Red-eyed Vireo, Blue Jay, Fish Crow, Purple Martin, Tree Swallow, Northern Rough-winged Swallow, Barn Swallow, Carolina Chickadee, Tufted Titmouse, Marsh Wren, Carolina Wren, Blue-gray Gnatcatcher, American Robin, Gray Catbird, Brown Thrasher, Northern Mockingbird, European Starling, Cedar Waxwing, House Sparrow, House Finch, American Goldfinch, Orchard Oriole, Baltimore Oriole, Red-winged Blackbird, Brown-headed Cowbird, Common Grackle, Prothonotary Warbler, Common Yellowthroat, Northern Parula, Yellow Warbler, Northern Cardinal, Indigo Bunting.

Probable - 8 Species: Chimney Swift, Least Bittern, Barred Owl, Hairy Woodpecker, Eastern Wood-Pewee, Acadian Flycatcher, White-breasted Nuthatch, Song Sparrow.

Possible - 22 Species: American Black Duck Yellow-billed Cuckoo, Common Gallinule, Spotted Sandpiper, Green Heron, Black-crowned Night-Heron, Red-shouldered Hawk, Red-tailed Hawk, Eastern Screech Owl, Great Horned Owl, Belted Kingfisher, Northern Flicker, Willow Flycatcher, American Crow, House Wren, Wood Thrush, Eastern Towhee, Louisiana Waterthrush, Kentucky Warbler, American Redstart, Scarlet Tanager, Blue Grosbeak.    

Present - 11 Species: Ring-necked Duck, Rock Pigeon, Ring-billed Gull, Caspian Tern, Forster's Tern, Double-crested Cormorant, Great Blue Heron, Great Egret, Black Vulture, Turkey Vulture, 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.

Larry Cartwright

Dyke Marsh Breeding Bird Survey Coordinator


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