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.
Northern Mockingbirds were always resident in Southern Delaware but were considered very rare in the Delaware Valley in the 19th century, mainly due to being collected as caged birds where birds were fetching prices between $7 and $20! Once it became illegal in 1913 to catch native species for the pet trade, the birds began to gradually move northwards and colonize our area. It was first recorded nesting in Pennsylvania in 1937 and by the 50’s they were considered permanent residents in PA, though still ‘thinly distributed’ in New Jersey until the 60’s when they became established.

Cardinals (right) were recorded breeding in Delaware and Southern New Jersey in the late nineteenth century but only began colonizing Southeastern Pennsylvania in the 1920’s. All three of these species can now be found in southern Canada, in small numbers.
Black Vultures (left) have greatly expanded their range northwards in recent decades. In the 1930’s they were first reported in Delaware and by the 1950s’ in New Jersey and Pennsylvania. They are now being seen as far north as Maine. Since vultures are primarily carrion eaters, could the increase in vehicles and road kills be contributing to this northward movement?

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.

all photos © adrian and jane binns

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