Experimental Restoration of Mid-Atlantic Coastal Grasslands
The landscape-scale CRFRS experiment in native grassland restoration of recently retired croplands began in 1999. Special priority was given to the restoration of the mid-Atlantic coastal grasslands that once dominated the eastern Atlantic seaboard in pre-colonial times but are now a virtually extinct habitat. After two centuries of tobacco cultivation, intensive grazing on exotic pasture grasses, extensive peach and cherry orchards, and forty years of row-crop rotation in corn, wheat, barley, and soybeans since WWII, 228 acres of relatively unproductive sandy, acid soils were placed under 15-year, renewable contracts with the Conservation Reserve Program (CRP) of the US Department of Agriculture and Conservation Reserve Enhancement Program (CREP) with the State of Maryland. Twelve replicated fields of 23+ acres (see map below) were planted in eight species of native warm-season grasses and two cold-season grasses in five seed-mixture treatments in April 1999.
Management protocols (herbicide, mowing, and fire) were designed so that several structures of grasslands (short, tall, mixed) might be maintained. We monitored the establishment and maturation of the grasslands, and measured the rates of colonization of new plant species (i.e. increases in the species diversity), changes in the relative abundances by percent cover, and rates of vegetative growth and reproductive performance of the principal prairie grasses. The matched colors on the map below depict the replicate experimental CRFRS fields.
Avian Grassland Demography Studies
Colonization of the restored grasslands by obligate grassland birds started within one month of planting - Horned Larks, Killdeer, and Grasshopper Sparrows appeared in April 1999 and immediately established territories, engaged in courtship, and nested successfully.
Other rare grassland birds, including Vesper Sparrow, Northern Bobwhite, and Dickcissel also colonized the Grasslands within the first two years, albeit in smaller numbers. Dickcissels have returned every year since. In 2004, 2005, 2010 and 2012 Sedge Wrens appeared and established late summer territories.
We directed our ornithological research effort toward Grasshopper Sparrows, to use them as bio-indicators of the differences, if any, in the value of the alternative prairie types we installed and managed. Our mist-netting techniques proved satisfactory - we have banded 865 adult and 1898 hatch-years on the CRFRS Grasslands in ten years, and another 200 in other nearby habitats.
All adult Grasshopper Sparrows are captured, and color-banded for easy field identification and observation. The breeding population is 70-80 pairs each summer; an additional 10-20 males are caught each year that do not set up territories. We infer that males have higher annual survival than do females, generating these excess males. In contrast to reports of birds in the Mid-West our territorial male GRSPs exhibit remarkable site fidelity, predictably returning to the same acreage as held previous years.
Breeding adults and HY Grasshopper Sparrows have returned to the CRFRS Grasslands at exceptionally high rates. Population structure seems to have stabilized since 2002 with an average of 45% of adults returning to the grasslands from previous years. We have confirmed a minimum average (since 2000) of 57% of adult males (a high of 81% in 2003), 32% of adult females, and 11% (a high of 18% in 2004) of marked HYs returning to the grasslands each year.
We estimate we catch about half of the annual production of the 360-400 nestlings from an estimated 120 successful nests on the grasslands each summer. In addition, we have seen several banded (USGS only) males on neighboring properties that we are confident are our HYs that have returned to the region but dispersed from the grasslands.