Racing time to characterize a community

CCB researchers estimate population sizes of unique community of birds supported by regional marshlands

Interior form of the Nelson’s sparrow captured in winter salt marsh along the western shore of the Chesapeake Bay.They exist as a world apart – utterly different from the familiar uplands just 100 meters away.  Walking through them has the feel of a Midwest prairie or West Texas grassland. With only the sound of water and wind, they feel empty and deserted. But they are not. The winter marshes of the Chesapeake Bay and surrounding mid-Atlantic coast support a unique community of birds.  A community that lives on borrowed time in the path of rising seas.

For three months during the winter of 2013-2014, a team of biologists from The Center for Conservation Biology led by Fletcher Smith have conducted more than 300 transect counts across the coastal plain in an attempt to sample the winter saltmarsh bird community. With funding from the Virginia Department of Game & Inland Fisheries, the project will be the first to estimate population sizes supported by regional marshlands. The estimates will serve as benchmarks or stakes in time against which to compare future population levels. Most abundant species include saltmarsh sparrow, Nelson’s sparrow, seaside sparrow and marsh wren. Other species include sora, clapper rail, Virginia rail, swamp sparrow, savannah sparrow, short-eared owl, northern harrier and American bittern.

Despite the fact that they are very specialized, threatened and essentially in our backyards, we know surprisingly little about these birds. Avoided by most people, marshes are not particularly inviting to the birding public. Even for those who venture into the marsh, they are only rewarded with occasional glimpses of a brown flash along the top of the marsh grass. Not much of a trophy for a long slog through the marsh.

Unlike many birds that seek safety in numbers during winter, the primary strategy of these species is to spread out and get lost in the uniform monotony of grass. Concealment is the key.  They stay hidden within the vegetation and can be very reluctant to flush, a characteristic that frustrates many birders and makes it challenging for biologists to estimate populations.

A unique, rope-drag transect approach was used to collect bird density information within winter marsh patches. Two biologists drug a weighted rope through the marsh, flushing birds within a standard transect, while two other biologists followed the rope and noted all birds flushed. This technique yields a reliable estimate of bird density that may be used in population projections.  The team also used the rope technique to maneuver birds into mist nets for banding.

Featured image: Interior form of the Nelson’s sparrow captured in winter salt marsh along the western shore of the Chesapeake Bay. Photo by Bryan Watts.

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This article was originally published March 27, 2014 on the CCB news website.