Breeding Bird Survey





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Results of the 2012 Dyke Marsh 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 on this his twentieth year as the Coordinator of the Breeding Bird Survey. This activity, a continuing biological inventory of the Dyke Marsh Wildlife Preserve, has provided trend information on the Marsh since the 1960's. The Friends also gave Larry a portrait of his beloved Prothonotary Warbler. President Glenda Booth presided.

Larry Cartwright

FODM President Glenda Booth awards a certificate of appreciation to Larry Cartwright.  Photo by Dorothy McManus.

The 2012 Dyke Marsh Breeding Bird Survey was conducted as part of a continuing biological inventory of this dwindling tidal wetland. The breeding status of each species was determined by means of behavioral criteria. Species were placed into one of four categories: confirmed breeder, probable breeder, possible breeder, and present.

    The official survey was conducted between Saturday, May 26, and Sunday, July 1, 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 to supplement data reported by the survey teams. The survey tract encompassed the Belle Haven picnic area, the marina, the open marsh, the Potomac River shoreline and the surrounding woodland from the mouth of Hunting Creek to Morningside Lane.  The volunteers reported 84 species at Dyke Marsh during the 2012 survey.  By the time data collection was completed, they had collectively categorized 39 species as breeders, eight species as probable breeders and 23 species as possible breeders.  An additional 14 species were present in the survey tract during the official reporting period, but were considered not to be in suitable breeding habitat.

Screech Owl

One of the breeding pair of Eastern Screech-Owls in Dyke Marsh.  Photo by Ed Eder.


    The Eastern Screech-Owl pair returned for a second breeding attempt in 2012 after last year’s highly successful nesting that produced three healthy fledglings.  The tree hosting the cavity in which the birds bred during 2011 fell down during the following winter, but the breeding pair found a suitable replacement nest cavity for the 2012 breeding season.  The gray morph male was first reported on March 24 in a cavity not more than 25 feet from the original nest site.  Unfortunately, the last observation was on May 6 as the developing foliage made the cavity and the owls more difficult to see. We did not document any fledglings and do not know the outcome of this year’s breeding attempt.

    The Bald Eagle breeding pair at the Morningside Lane nest did well again this year, fledging three healthy youngsters by June 8.  The fledglings perfected their aerodynamic skills during the next week and a canoe team reported the birds in flight near the nest
Osprey at nest

One of three Osprey nestlings on the rootball nest.  Photo by Roger Miller.

on June 17.  Five of nine Osprey nests produced young this year.  Three of the successful nests, including the well-known and closely observed marina nest, were on platforms, one was on a root ball and one was constructed in a tree. The most interesting nest for me was the successful root ball nest that is situated between the two islands just south of the marina.  Here three nestlings and their unconcerned parents calmly watched while canoeists passed as close as five feet from the nest to inspect the growing youngsters.  It appears that both adults and nestlings perceived no malicious intent on the part of the canoeists and adapted well to human presence, as have the marina Ospreys.  The ability of some birds to adapt is positive, but may also make them vulnerable to anyone wishing them harm.  Fortunately, I am aware of no instances at Dyke Marsh where humans have deliberately tried to hurt or harass breeding Ospreys.

Purple Martin

Purple Martins nest under the Osprey platform at the marina.  Photo by Ed Eder.


    Even after 20 years of conducting the survey, I am sometimes amazed and even entertained by what we find while in the field.  This year it was nesting Purple Martins.  Purple Martins nesting in gourds or bird house apartments erected for them are hardly a new phenomenon, but the location and circumstances were quite unique at Dyke Marsh because the birds bred at the base of the Osprey nest in the marina.  It just so happens that the slats or dividers in the platform that supports the nest served as nice nesting compartments for the Purple Martins.  The birds were first noted hanging around the nest platform on June 1 and within a few days were actively bringing nesting material into the compartments.  The collected data indicates that a minimum of six breeding Purple Martin pairs were nesting in the platform.  We observed fledged young around the nest site in the company of well over a dozen adults on August 5.  The breeding Ospreys seemed to take little notice and certainly did not interfere with the species sharing the platform with them.  The story ended on a happy note for all as both Ospreys and Purple Martins successfully fledged young.

Yellow Warbler

An adult Yellow Warbler is observed feeding one of its five nestlings.   Photo by Ed Eder.


An active Yellow Warbler nest within a yard of the boardwalk also delighted both survey teams and participants in the Sunday morning walks. An observer first documented the boardwalk nest on June 4, which was followed by reports of five nestlings a few days later. The leader of one Sunday morning walk stated that the male Yellow Warbler would fly into the nest with a mouthful of food and then sing for a moment before feeding the nestlings. This nest provided another success story as volunteers reported on nestling growth, development of feathers and finally fledging as youngsters began departing the nest on June 13. In this case, fledging appeared to be a two-day event, as three of the young left the nest on June 13 and the remaining two the following day. It has been my understanding that songbird nestlings fledge simultaneously, but such it would seem is not always the case.

    Among the most prolific breeding migrant songbirds at Dyke Marsh are Eastern Kingbirds, Warbling Vireos and Orchard and Baltimore Orioles.  When I first began compiling the data for this survey in 1993, Warbling Vireos were confined to a few breeding pairs in the picnic area, but have now expanded throughout the area covered by the survey.  I believe that up to 18 territorial males present in 2012 would not be an unreasonable estimate.  Despite the ease of picking up singing males, Warbling Vireo nests remain incredibly hard to find.  This year’s survey yielded one documented Warbling Vireo nest.  It was located in a sycamore tree beside the bridge on the Haul Road peninsula and presumably produced the two fledglings found in the area with their parents on June 30.  The sycamore tree that hosted the Warbling Vireo nest also was popular with both oriole species in 2012 and provided nest site locations for at least one Orchard Oriole breeding pair and two Baltimore Oriole pairs.  Despite the proximity of the oriole nests, all of which were active simultaneously, the breeding pairs displayed little interaction toward each other.  Indeed, tolerating nearby nesting pairs with no evidence of territorial hostility seems to be an attribute of at least some, if not most, breeding orioles at Dyke Marsh.

Eastern Kingbird

An Eastern Kingbird brings building material to its nest near the water.  Photo by Ed Eder.


    Eastern Kingbirds building nests along the water’s edge often place them in fairly open locations that provide particularly good views for canoe-based survey teams.  This was true again in 2012 as nests with young near the boardwalk and Pipeline Bay were well documented by several canoe teams.  The young are highly visible even at rest.  They also can become noisy and competitive with nest mates when parents bring them food.  Another advantage to being in a canoe is that even if things get fairly quiet, there is a host of Red-winged Blackbirds in the area that you can watch building nests, carrying food or tending to fledged young.  There is always something to delight the senses on the water.

Canoe teams also often get the best views of three high-visibility bird species -- Prothonotary Warblers, Marsh Wrens and Least Bitterns.  In the case of Prothonotary Warblers in 2012, canoeists found a nest while foot teams documented the results of successful breeding.  A canoe team observed an active Prothonotary Warbler nest on May 27 at a location we happen to call Prothonotary Bay just inside the Big Gut entrance and in June, foot teams reported adults feeding fledged young north of Pipeline Bay and at the dogleg.

The fate of Marsh Wrens and Least Bitterns remain in doubt at Dyke Marsh, but the trend suggests eventual disappearance for at least the Marsh Wren.  Marsh Wren nests were found in the channel separating the marsh vegetation between the Haul Road peninsula and the main island in 2012, but data analysis indicate that only approximately eight territorial males were present.  In 2011, I estimated that 10 males held territories in this part of the marsh.  A tributary of the Big Gut in the south marsh also hosted at least one nest in 2012, but canoe teams reported no more than two singing Marsh Wrens.  Least Bitterns were difficult to locate in the north marsh during 2012, with even canoeists reporting no more than a single bird during each weekly survey.  The south marsh provided a little more hope, with four individual birds and a possible breeding pair documented on June 10, but subsequent surveys yielded no Least Bittern nests or fledged young.

2012 was my 20th year as compiler of the Dyke Marsh Breeding Bird Survey, but there are so many wonderful volunteers who have participated over the past two decades that have made the survey possible.  In particular, I would like to make special mention of Don Robinson and Elizabeth Ketz-Robinson who have participated in almost every weekly survey since 1993. They are truly special.  With that, I would like to recognize those who took part in the 2012 survey, whether they actively participated on a survey team or provided supplemental data during a Sunday morning walk.

In alphabetical order, they are Eugene Ballering,  Andy Bernick, Dave Boltz, Glenda Booth, Julie Bourns, Monique Derfuss, Ed Eder, Myriam Eder, Sandy Farkas, Kurt Gaskill, Susan Haskew, Gerry Hawkins, Jackie Howard, Beth Kemick, Phil Kenny, Elizabeth Ketz-Robinson, Mary Alice Koeneke, Glen Koppel, Ginny McNair, Larry Meade, Roger Miller, David “Nick” Nichols, Kurk Petrovic, Laura Plaze, Marc Ribaudo, Rich Rieger, Don Robinson, Alex Ronkainen, Molly Ross, Peter Ross, Paula Sullivan, Kim Taylor, Margaret Wohler and Chris Wolz.

    The 2012 Breeding Bird Survey Results:

    Confirmed - 39 Species: Canada Goose, Wood Duck, Mallard, Osprey, Bald Eagle, Mourning Dove, Eastern Screech-Owl, Red-bellied Woodpecker, Downy Woodpecker, Great Crested Flycatcher, Eastern Kingbird, Warbling Vireo, Blue Jay, Fish Crow, Purple Martin, Tree Swallow, Northern Rough-winged Swallow, Barn Swallow, Carolina Chickadee, Tufted Titmouse, White-breasted Nuthatch, Carolina Wren, Marsh Wren, Blue-gray Gnatcatcher, American Robin, Gray Catbird, European Starling, Northern Parula, Yellow Warbler, Prothonotary Warbler, Northern Cardinal, Red-winged Blackbird, Common Grackle, Brown-headed Cowbird, Orchard Oriole, Baltimore Oriole, House Finch, American  Goldfinch, House Sparrow.
    Probable - 8 Species: Least Bittern, Eastern Wood-Pewee, Acadian Flycatcher, Willow Flycatcher, Red-eyed Vireo, Common Yellowthroat, Song Sparrow, Indigo Bunting.
    Possible - 23 Species: Green Heron, Cooper's Hawk, Red-tailed Hawk, Killdeer, Spotted Sandpiper, Yellow-billed Cuckoo, Chimney Swift, Ruby-throated Hummingbird, Belted Kingfisher, Hairy Woodpecker, Northern Flicker, Eastern Phoebe, American Crow, House Wren, Northern Mockingbird, Brown Thrasher, Cedar Waxwing, Black-and-white Warbler, Ovenbird, Louisiana Waterthrush, Scarlet Tanager, Eastern Towhee, Chipping Sparrow.
    Present - 14 Species: Tundra Swan, Canvasback, Double-crested Cormorant, Great Blue Heron, Great Egret, Black Vulture, Turkey Vulture, Black-bellied Plover, Ring-billed Gull, Herring Gull, Great Black-backed Gull, Caspian Tern, Forster's Tern, Rock Pigeon.

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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Last Revised: July 27, 2013