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Harvard Forest Symposium Abstract 2012

• Title: Breeding Birds of the Harvard Forest, 1993 vs. 2011
• Primary Author: Daniel Steven Cooper (Cooper Ecological Monitoring, Inc.)
• Abstract:

  I conducted a breeding bird survey using 75 fixed-radius point counts in the Prospect Hill Tract of the Harvard Forest during two summers 18 years apart, 1993 and 2011. Excluding fly-overs, I recorded approximately 1,300 individual birds each year representing 51 species in 1993 and 54 species in 2011. These data may also be compared with bird observations from the forest in 1948 and 1970 in notes archived at the Harvard Forest. To quantify bird community change from 1993 to 2011, I used the average number of individuals of each species detected at each point over two visits per year (June/July 1993; June 2011), which produced a “detection probability”. These probabilities were then compared to determine which had increased, which had declined, and which were present in similar numbers since 1993. Six bird species were among the 10 most numerous species in both 1993 and 2011: Red-eyed Vireo, Black-capped Chickadee, Scarlet Tanager, and three species of wood-warblers, Ovenbird, Black-throated Green Warbler, and Black-throated Blue Warbler. These may be said to form the “core” songbird community of the Prospect Hill Tract, which is dominated by the Ovenbird, detected at nearly twice the level as the next most common species, the Red-eyed Vireo in both years. All 75 survey points had at least one Ovenbird in either 1993 or 2011, and this species accounted for nearly one-quarter of all bird detections in each year (23%, 24%, resp.). Though the data await a more rigorous analysis, several species showed differences in abundance from 1993 to 2011 that are likely significant. Among the biggest increasers was the Pine Warbler, whose detection probability jumped from .007 (a single pair) in 1993 to .533 in 2011, when it was detected at just over half the survey points. Other increasers in 2011 included the Yellow-bellied Sapsucker (0/.113) and Indigo Bunting (.013/.107). Species showing the greatest declines 1993 to 2011 included the Dark-eyed Junco (.127/0), Blue-headed Vireo (.340/.080), and Winter Wren (.147/.053). Many of the bird species that declined or were totally absent in the 2011 survey are associated with mature coniferous forest, such as native spruce/hemlock and pine plantation habitat, including the Yellow-rumped Warbler, Red-breasted Nuthatch, Golden-crowned Kinglet (absent 2011), Magnolia Warbler (absent 2011), and Purple Finch (absent 2011), in addition to the three declining species mentioned above. The increase in the Pine Warbler would seem to counter this trend; however, its increase appears to be part of regional recent expansion of this species throughout New England, illustrating the difficulty of linking local land use practices to observed bird community turnover at any one site. Furthermore, species that increased in abundance in 2011, including those that appeared in 2011 after being absent in 1993, exhibit a range of habitat preferences, with some typical of deep forest, and others favoring forest edge such as that provided by recent clear-cuts.

• Research Category: Biodiversity Studies
  Conservation and Management
  Historical and Retrospective Studies