Range Expansion into the Delaware Valley
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Feb 10, 2009 | by Adrian Binns
Some ‘southern’ species have naturally expanded their range northwards. The increase in backyard feeding stations surely has something to do with this expansion as it has made it easier for some species to survive the winters, but on the other hand could global warming be the primary reason?
Though there were rare reports of Red-bellied Woodpeckers (left) in the tri-state area (PA, NJ and DE) as early as the late nineteenth century, and breeding records in the early twentieth century, it was not until the 1950’s that they expanded their range northwards from the southeast into the Delaware Valley.
Boat-tailed Grackles (above) are coastal birds that have edged northwards from the Carolina’s since the late 19th century. Prior to 1950 there were only 4 New Jersey records, though they were breeding a little further south in Delaware by the mid 1930’s. By 1982 they had successfully colonized the Atlantic coast in New Jersey as well as the lower Delaware Bay shore and had reached Long Island.
Brown-headed Nuthatches were first recorded in Delaware in 1903-04, making this the very northern edge of its range. They favor loblolly pines whose northern limits also happen to be here. While the previously mentioned species seem to be expanding their range northwards, the nuthatch is in decline.
The most recent species to colonize our area is the Cattle Egret (left) which reached Florida in the 1940’s and our area by the mid 1950’s with breeding records shortly thereafter. Though their numbers have fluctuated and they are very sporadic in our area. The largest concentration of Lesser Black-backed Gulls in the United States in centered on the Delaware Valley (though no confirmed breeding pairs in the US), with numbers sharply increasing each winter in our area since 2000. These are good examples of worldwide natural range expansion.
So what is the next species? Could it possibly be the Eurasian Collared Dove, a species that reached Florida in the early 1980’s after being introduced to the Bahamas in 1974. It has been expanding its range north and westwards ever since.