2007 Dyke Marsh Breeding Bird Survey Results

The 2007 Dyke Marsh Breeding Bird Survey was conducted as part of a continuing biological inventory of this productive, but fragile and now shrinking tidal wetland.  The official survey was conducted between Saturday, May 26 and Wednesday, July 4.   The volunteers documented 79 species at Dyke Marsh during the 2007 survey. By summer’s end, they collectively confirmed 35 species as breeders, tallied 11 species as probable breeders, and reported 21 species as possible breeders.

Marsh Wren at Nest - photo by Ed Eder

             The fortunes of 2 high-visibility species, the Marsh Wren and Least Bittern, may be in grave doubt.  Last year, I reported that the 5-year decline in the Marsh Wren population apparently had ended and that the birds seemed to be recovering. A dozen territorial males, up from 8 or 9 in 2005, occupied the north marsh around Haul Road and a small group of males established territories in the Big Gut for the first time since 2001. The volunteers discovered active nests at both locations.  Unfortunately, the recovery seems to have ended. No Marsh wrens were documented in the Big Gut in 2007 and a mere 6 territorial males were present in the marsh vegetation on Hog Island and the northern shoreline of Haul Road. The first male was not even tallied until 9 June.  The population of Marsh Wrens now seems more perilous than at any time since I became compiler 15 years ago.       

The status of the Least Bittern is even more surprising. Unlike the Marsh Wren, the Least Bittern seems to have consistently maintained a robust population.  For example, last year the volunteers documented approximately 13 territories and confirmed the species as a breeder when adults were spotted at two locations gathering food for young.  In contrast, 2007 was a poor year for Least Bitterns.  Despite diligent searching, the volunteers in 2007 documented only a possible breeding pair at the end of the peninsula on Haul Road, another possible breeding pair on Hog Island, a single bird in the Little Gut, and another lone bird near the mouth of the Big Gut.

            On a more positive note, Ospreys are a genuine success story at Dyke Marsh. The volunteers noted 11 nests dispersed throughout the survey area.  Seven of these produced healthy fledged youngsters by the end of the breeding season.            

            As for neotropical migrant songbirds, Eastern Kingbirds, Orchard Orioles, and Baltimore Orioles continue to prosper.  Barn and Tree Swallows, as usual, nested successfully.  Also, if Marsh Wrens and now possibly Least Bitterns are a cause for concern, Prothonotary Warblers should be a source of great joy.  The volunteers documented two active Prothonotary Warbler nests, one in the upper portion of the Big Gut and the other in the south marsh, and adult birds were observed either feeding youngsters or carrying food at three additional locations.

             Confirming nesting songbirds is always difficult at best, but 2007 was an absolutely trying experience for the survey participants.  Even the Yellow Warbler, normally confirmed in May, was not documented until July 8 when an adult was observed feeding a fledgling just north of the Dogleg.  Warbling Vireos, which have dramatically increased over the past few years, Red-eyed Vireos, Northern Parulas, and Common Yellowthroats were all on territory during the survey period, and numerous observers reported the presence of breeding pairs of all 4 species. Yet we were unable to confirm any of them.

Belted Kingfisher - Photo by Ed Eder

             One of the most interesting stories of the 2007 survey was the first recorded breeding attempt by Belted Kingfishers at Dyke Marsh.  These boisterous birds generally dig their nest burrows in steep slopes along rivers where there is a plentiful supply of aquatic life to feed their nestlings.  Steep riverbank slopes are nonexistent at Dyke Marsh, so I was fascinated when I received a report on 24 March of a Belted Kingfisher pair attempting to construct a burrow in a rootball of a fallen tree just south of the marina.  The birds labored over their task for perhaps a week before abandoning the effort.

             Northern Rough-winged Swallows prove to be a more interesting dilemma.  Almost every year in late June, the volunteers report the presence of dependent youngsters perched on snags being feed by their parents.  Suitable breeding habitat is available for this species and I have witnessed young birds emerging from burrows on one occasion.  However, in most years, observers make few reports of Rough-winged Swallows as being present until dependent fledglings make their appearance late in the survey.  Several people have voiced opinions for and against listing this species as a confirmed breeder.  My evidence suggests that dependent birds disperse no more than a mile from their natal area.  At best, we can say that if Dyke Marsh was not the origin of these young birds, then it was from an area very close by. At the very minimum, adult Northern Rough-winged Swallows routinely avail themselves of the resources at Dyke Marsh to feed their young in the period just before fledgling independence.

Larry Cartwright
Coordinator, Dyke Marsh Breeding Bird Survey

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 in suitable habitat or out of its breeding range.
Definition of Safe Dates: We have adopted 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.

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Last Revised: April 25, 2008