Human Population and Bird Habitat
Of the many reasons given to explain the decline in some bird species such as warblers, thrushes, shore birds and grassland birds, habitat loss seems to emerge as the primary cause. Some species require large uninterrupted tracts of forest, grassland, marsh or beach and cannot thrive in small, limited islands of habitat. At the same time, there are some species of birds that do well in the edge habitat provided by the fragmentation of woodlands by suburban sprawl. The burgeoning population of the common crow is due, in some part, to the fragmentation of woodlands.
In order to get a sense of how urban development has overtaken our region, look at the series of maps of housing density (See sidebar "Density Population Maps") that represent a residential density of three houses per 2.5 acres. On Long Island, it appears that only parks, the pine-barrens preserves, wetlands and some remaining farmland remain free of development. The same is true for New Jersey and the Connecticut coast and river valleys. Steep topography remains a limiting factor for dense development. The risks associated with living on a barrier beach do not seem to limit dense development.
The very sharp decline of grassland birds in the mid-west stems from changes in agricultural crops and mowing/harvesting practices. Double cropping - getting two crops a year on a single tract of farm land - means mowing or harvesting early in the summer when birds still have young in the nest. Here in the east, many fields of hay and alfalfa have been converted to housing tracts.
One of the first large development tracts, in the New York City metropolitan area, was Levittown. This development was built on the largest natural grassland in the northeast; the Hempstead Plains.
The grassland birds had some nesting habitat in the hay fields of the dairy farms in New Jersey and upstate New York. Also, many airports cover vast tracts of land, and are, in effect, man-made grasslands which still support ground-nesting birds such as upland sandpipers, meadowlarks and grasshopper sparrows. Now, some older and obsolete airports are being decommissioned and converted into industrial parks and shopping malls.
From the mid-1970s into the '80s there were breeding grassland birds such as grasshopper sparrows, meadowlarks, upland sandpipers, American kestrels and northern harriers from Southern New Jersey to the eastern tip of Long Island. That range includes New York City itself. In New York City, the last record for a nesting short-eared owl - another ground-nesting grassland bird - was in 1981 in Floyd Bennett Field. Although short-eared owls continued to breed in New Jersey and on Long Island for a few years after that, they no longer do.
As open space surrounding some breeding bird habitat becomes covered by development, some birds may return to raise their young where they have been successful in the previous season. This return to less than optimal habitat is called site fidelity. But such diminished space is unlikely to attract replacements once the holdouts die off or nesting failure occurs. The smaller the continuous open space, the less likely it is to attract a first-time grassland bird breeder.
The desire for some open green space around their homes also seems to be one of the reasons why people want to move to the suburbs and beyond. The developers claim to be meeting the housing demands of the increasing population in this and other metropolitan regions but that does not account for the rate of urban sprawl. Between 1970 and 1990, while urbanization in this region increased by 65%, the actual population increased by only 8%. An expansive road system, economically marginal farms, cheap energy and water have facilitated the sprawl into the region's open space. Some of these very same factors may, eventually, define the limits of development. The availability of clean water from wells has already set some limits on Long Island. But the damage has been done and developed land will not revert to open fields and woodland.
Some of the bird nesting habitat loss from urban sprawl will be reflected in the data coming out of the 2000 to 2005 New York State Breeding Bird Atlas when compared to the same type of breeding bird survey done from 1980 to 1985. The sharp decline in breeding grassland birds in this region will become apparent. Undeterred by all the loss of habitat in this region, the New York City Audubon Society will continue to make every effort to preserve and protect wildlife habitat here in the five boroughs of New York City.