This fall has been notable for the scarcity of birds. Baldpate Mountain, the Sourland Ecosystem Preserve, Cedar Ridge, St. Michaels’s, the Watershed Institute, and Mount Rose Preserve, the places I normally see good numbers of fall migrants, have been strangely quiet. The lack of warblers has been especially notable. One wonders where they have gone.
Along the eastern migration corridor, the traditional fall migration pattern for long distance migrants is that hatch year birds follow the coast and mature birds follow the mountains. Migration is partially innate and partially learned. Following the coast is innate. Birds that survive the first winter follow mature birds north along the mountain route, learning as they go.
It is possible that young birds have been pushed inland by the unsettled weather patterns this fall. Radar studies of migrating birds have shown birds being pushed into the central flyway this fall both before and during the atmospheric disturbances caused by Florence. Birds are very sensitive to atmospheric pressure and will alter course to avoid areas of low pressure. More normal flight patterns resumed after Florence. Unfortunately, radar gives no information on demographics.
Bird banding stations which study demography are essential for determining if the birds are changing route or if there was widespread nesting failure. Most fall migrants studied at Hannah Suthers’ Featherbed Lane Bird Banding Station in the Sourlands are hatch year birds, a pattern that has held for four decades. The majority of fall migrants studied at the Powder Mill Bird Banding Station in western Pennsylvania are adult birds. This fall the number of birds at Featherbed Lane is significantly down, but Powder Mill is reporting only a small decrease in the number of birds. While banding records show that the number of birds and number of species are showing long term declines, sharp short-term declines are especially worrisome since they may indicate widespread nesting failure.
This summer Featherbed Lane showed the lowest population recruitment in the history of the banding station. The summer of 2017 had the second lowest population recruitment. A wet late spring followed by a brutally hot summer may have been a factor in 2018. Hopefully, this extreme weather pattern is not the new normal. A study in California showed that resident birds were tracking global warming but that migrants were not, indicating that migrants will be especially hurt by climate change. The Featherbed Lane data supports this study, showing low numbers of hatch year Neotropical migrants, especially warblers and thrushes. In contrast, resident woodpeckers had a good breeding season. Juvenile pileated woodpeckers were the bright spot in an otherwise drab and depressive breeding season.
Habitat loss, degradation, and fragmentation continues to be the primary cause of bird decline both on the breeding and wintering grounds. Despite active measures to improve habitat at Featherbed Lane, habitat quality continues to decline, largely due to the opening of the canopy by dying ash trees and the subsequent invasion of Japanese stilt grass. Unfortunately, this scenario is playing out over the entire central New Jersey region as ash trees succumb to the Emerald Ash Borer, opening up the understory to non-native invasive plants. Birds that depend on the leaf litter for nesting and feeding are especially affected as the thick growth of the stilt grass denies the birds’ access to the leaf litter. Ovenbirds are declining where stilt grass is invading and are eliminated in areas of heavy growth.
The data shows that bird numbers are down this year and indicates that nesting failure was a factor in this decline. Bird banding station data is essential in documenting this decline. Since bird banding stations are few and far between, eBird data is essential in determining if the banding station data is local or reflects regional trends. While it is not as much fun to bird when birds are scarce, the data collected is essential to solve the puzzle of bird decline.
~ Sharyn Magee