Tuesday, September 05, 2006

75 Black Terns on the Delaware

On this day in 1907, Richard C. Harlow and Richard F. Miller found about 75 Black Terns on the Delaware River behind Petty's Island at Camden. They took six specimens and all proved to be immatures. Miller stated that all the birds they saw were juveniles, but since immature plumage and adult nonbreeding plumage are similar in this species, it is possible that there were some adults mixed in. These were the days of shotgun ornithology.

On 10 September 1907, Harlow and Miller saw 50 Black Terns in this location and at Philadelphia; on that occasion, eight specimens were taken. Again, all the birds that were shot were immatures. The specimens were kept by Harlow and Miller for their collections, except for two that were given to Witmer Stone for his collection. Miller concluded by saying, "The Terns were undoubtedly a migrating flock driven inland by a recent storm." Reference to 1907 hurricane data here does not show any hurricanes near the time of these sightings, so it must have been a different kind of storm system. One also wonders whether the terns were "driven inland," or just grounded by the storm.

This observation may gain extra interest because of the recent fallout of Black Terns across NJ. Most concentrations of migrating Black Terns are found on the coast; the unusual aspect of the recent Black Tern fallout is the fact that terns were found in such locations as Spruce Run Reservoir in Hunterdon County and Assunpink WMA in inland Monmouth County. Walsh et al's Birds of New Jersey gives a high count of 50 individuals found at Hancock's Bridge in Salem County on 14 August 1994. As Dasey says in his 1994 fall season report in Records of New Jersey Birds, "Aug. 14 brought the heaviest Black Tern movement to hit the region in many years...Subsequently, it was shown the movement was widespread, stretching from the NJ coast into at least central Pennsylvania." He also mentions 9 individuals at the mouth of Pennsauken Creek at Palmyra and 5 more at Mannington, but does not link the terns with a particular weather pattern.

However, on the same day, 65 Black Terns were seen at Donegal Lake in Westmoreland County, Pennsylvania, "after a heavy afternoon thunderstorm," according to McWilliams and Brauning's The Birds of Pennsylvania. The "coincidence" of large flocks of Black Terns being seen on the same day in places as widely separated as Salem County, NJ, and Westmoreland County, Pennsylvania, starts to raise even more questions. Did weather conditions concentrate the terns in an unusual way? Or was it just a good year for Black Tern production, leading to more birds coming south, which might then be grounded by localized weather systems? Without a deeper search into the local ornithological literature and archives of weather records, these questions will probably remain unanswered. It sounds like a worthy research project, however.

Dasey, Ward W. 1994-5. 1994 Fall field notes, Region 4. Records of New Jersey Birds 20:97-99.
McWilliams, Gerald M., & Daniel W. Brauning. 2000. The Birds of Pennsylvania. Comstock, Ithaca, NY.
Miller, Richard F. 1908. The Black Tern at Camden, N.J., and Philadelphia, Pa. Auk 25:215-216. PDF here
Walsh, Joan, Vince Elia, Rich Kane, & Thomas Halliwell. 1999. Birds of New Jersey. New Jersey Audubon Society, Bernardsville, NJ.

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