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The Dyke Marsh Breeding Bird Survey
Some Trends

The 2004 Dyke Marsh Breeding Bird Survey is now complete and the raw data is now being entered into the database. After a decade of being the compiler, we are able to see some trends in the breeding avian population. The survey volunteers have gained a familiarity with the marsh unequaled by any similar group in northern Virginia. They, including Kurt Gaskill, Rich Rieger, and Paula Sullivan, to name a few, have devoted many hours and considerable effort into making the survey a success.

Ospreys are the prime success story at Dyke Marsh.  When I assumed the role as compiler in 1993, the marsh hosted a maximum of 4 nests and at least 2 of these consistently fledged young.  We can now proudly boast at least 8 nests with at least 4 producing nestlings to the fledgling stage.  A very satisfying trend indeed!

Least Bitterns and Marsh Wrens have always been high visibility species at Dyke Marsh.  Least Bitterns appear to have a stable population.  Least Bittern nests are extraordinarily difficult to locate, but the expertise gained by the volunteers has given them the insight to know when and where to look for family groups.  The canoe surveys conducted by Kurt Gaskill and Chip Johnston and Don Robinson, Elizabeth Ketz-Robinson, and I during July have become a routine part of the survey protocol.  Due to time constraints, the Robinsons and I limit our survey activity to the Big Gut, but Kurt and Chip investigate the entire marsh.  They have been successful in locating up to 3 family groups or breeding pairs during these outings. 

Marsh Wrens, unfortunately, are a cause for concern.  I estimate that Dyke Marsh was home to over two dozen territorial males in the 1990s, but in 2000 the number of breeding males dropped by 60% to 70%.  The cause is still being debated.  The population appears to have slowly recovered and stabilized at perhaps over a dozen territorial males.  Breeding activities, however, are no longer distributed over the entire marsh as in the past.  The heaviest concentration is now on the islands and the marsh vegetation to the north of Haul Road.  I will feel considerably better when the Big Gut and the south marsh fill in with breeding Marsh Wrens once again.

When one thinks of the picnic area, Warbling Vireos instantly come to mind!  This area has been the prime concentration for this species over the years, with up to 4 breeding pairs present, and Paula Sullivan, Kurt Gaskill, and Ed Eder have been particularly successful in finding nests or fledged youngsters.  Eastern Kingbirds and Orchard and Baltimore Orioles, by contrast, can be found anywhere in the open wooded areas, and except for a major oriole breeding failure in 1998, these 3 species have no difficulty churning out the youngsters.

When turning to woodpeckers, I think of Rich Rieger because he is generally the guy who discovers the first Downy Woodpecker nest!  They and Red-bellied Woodpeckers are confirmed every year as breeders while Northern Flickers, and Pileated and Hairy Woodpeckers are documented as breeders slightly less than yearly.

Acadian Flycatchers and Eastern Wood-Pewees are now being documented more frequently as breeders, but this may be more a function of the growing expertise of the volunteers rather than the fact that these species are recent breeders at Dyke Marsh.  Great Crested Flycatchers, on the other hand, may indeed be new arrivals, and have been documented as breeders within the past 3 years.  Although there have been no successful breeding attempts that I am aware of during this time, they are definitely being observed more frequently. 

Yellow Warblers are yearly breeders at Dyke Marsh and concentrate their nests along the brushy areas along Haul Road while Prothonotary Warblers are generally confirmed every year, although we dipped on this species in 2004.  The evidence suggests, however, that the Prothonotary Warbler breeding population is stable, or perhaps even slightly increasing, in the southern marsh where are numerous snags that are a prerequisite for their breeding success.  Red-eyed Vireos are now being confirmed as yearly breeders, with at least one or two nests being discovered during the last few years.  Again, this is most likely a result of the expertise of the volunteers.  Northern Parulas and Common Yellowthroats are not confirmed on a yearly basis, but the nests of these species or their fledglings can be extraordinarily hard to locate, even with trained eyes and ears.  However, singing parulas and yellowthroats are present during every season.

Barn and Tree Swallows are consistently documented as breeders while the Northern Rough-winged Swallow makes the breeding list occasionally.   Tree Swallows use the nest boxes along the north shore of Haul Road and this year occupied 2 of the 4 boxes erected by Chip and Kurt across from the marina.  Several of the volunteers, including Linda Millington, Sandy Farkas, and the Robinsons and I, have located breeding pairs in natural snags.  Barn Swallows have faced a particularly hard time of it over the last two years, at least the ones using the foot bridge crossing the Big Gut in the south marsh.  Two consecutive wet springs in 2003 and 2004 produced unusually high tides that washed the nests out from under bridge.  Yet these guys persisted in trying again and Kurt Gaskill found Barn Swallow nestlings during the last week in August 2003.  If I am not mistaken, this late date may set a Virginia record for an occupied Barn Swallow nest.

Finally, let's look at one species that may very soon be elevated to the confirmed breeder status at Dyke Marsh.  That is the Indigo Bunting.  In 2002 territorial Indigo Buntings were noted along Haul Road and brushy locations in the south marsh.  They were also present during the 2003 and 2004 seasons.  Only one female has been observed during this period, but I am fairly confident that a documented breeding attempt is in our near future.  A welcome addition to our avifauna to be sure!

  Overall, with the possible exception of the Marsh Wren, the picture at Dyke Marsh currently seems fairly good despite numerous threats such as invasive nonnative plants and persistent erosion that degrade the ecosystem.  But what of the future?  How will the introduction of the snakehead into the Potomac affect fish species that are the prey base for Ospreys?  What will be the impact of the new construction on the Maryland side of the river?  The long term effects of the new bridge and increased siltation?  Potential new and unforeseen sources of pollution?  Well, with the baseline provided by the breeding bird survey and Kurt's weekly records, a long term negative trend will now be apparent.  How we react to it will be purely up to the Friends of Dyke Marsh, concerned citizens, and the National Park Service.

Submitted by Larry Cartwright

Dyke Marsh Breeding Bird Survey Coordinator      

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