President's Corner | Sharyn Magee
Warblers seemed everywhere in Central America in late November. Our North American breeders are spread out over a large area in the breeding season but in their wintering grounds in Central America, they are concentrated and very noticeable despite the lack of song and the muted colors of many species. Warblers are the most noticeable of our Neotropical breeding birds, but a closer look finds vireos, thrushes, flycatchers, and others among them. Central America is essential to these unsustainably declining birds.
Many of the birds seen in Central America seem familiar. Seventeen of the thirty-eight warbler species that overwinter in Central America breed in the Greater Sourland Important Bird Macrosite. Other central New Jersey breeding passerines that overwinter in Central America include two orioles, six flycatchers, five swallows, the blue-gray gnatcatcher, and two thrushes. Black and Turkey Vultures are abundant, Ruby-throated Hummingbirds mix with the local species, and familiar herons gather in wetlands and waterways. The list goes on.
It seems strange to see Hooded Warblers sitting on a fence post in the open and Kentucky Warblers sulking at the edge of the lawn, but birds don’t necessarily use the same habitat in winter that they use for breeding. Mature birds take the prime habitats in both the breeding and wintering grounds. Immature birds are left with the poorer habitats. Male and female birds of some species have differing winter habitats. In one study, Hooded Warbler males outnumbered females eight to one in primary forest, but females edged males out in secondary forest. A study of overwintering Redstarts in the West Indies showed adult males taking the best habitat, a forested area, and females and immature birds using substandard habitat, a garbage dump. This is an extreme case, but differential habitat quality is a factor in the higher survivability of adult birds and the high mortality of young birds. Most young birds do not survive their first year.
The Neotropical region is undergoing rapid deforestation. Primary growth forest is rare and becoming rarer. While many Neotropical migrants use second growth forest, new second growth forest is not keeping pace with loss of primary forest, resulting in a net loss of forest habitat. Land cleared for pasture is not suitable for forest birds but will support a variety of flycatchers and seed eaters. Land cleared for monocultures are strongly depauperate in bird species. Palm oil plantations are virtually devoid of bird life. Coffee has driven the rapid deforestation of the highlands. When sun grown coffee is converted to shade grown coffee, habitat is restored. When the understories of primary forests are destroyed and replanted in shade grown coffee, habitat quality decreases. The highest quality coffee is shade grown on the rich volcanic soils of Northern Central America and Europeans have developed an insatiable appetite for it, resulting in much habitat degradation. The factors driving habitat destruction and degradation are complex with the net result that major habitats are changing faster on the wintering grounds than on the breeding grounds.
According to ornithologist Douglas Morse, two-thirds of the breeding bird populations in many areas of North America winter in the tropics and half winter in a limited area in Mexico, northern Central America, and the West Indies that is one-seventh to one-eighth the size of the breeding grounds. The wintering ranges of many Neotropical migrants are entirely within this region. The density of migrating Neotropical birds drops rapidly south of northern Central America. Northern Central America, adjacent parts of Mexico, and the West Indies are essential for conserving these Neotropical migrant species.
Looking out the window at the grayness of winter, thoughts turn to spring and inevitability to birds and plants. Winter is a good time to take stock of the property and plan for the spring’s gardening. Intelligent gardening is applied ecology. Gardens play an increasingly important role in protecting our unsustainably declining biodiversity as too much habitat has been lost, fragmented, or degraded and increasingly our wildlife has no place to go. Even for obligate forest interior bird species, a well planted garden can be a welcomed migration stop. Birds need food, cover, and water. A well-planned garden can provide those needs.
If I want a healthy bird population on my land, I need a healthy diversity of native plants that attract a healthy diversity of native insects, not alien plants that produce toxins to which native insects have not adapted. I need to garden organically so I don’t poison the invertebrates that are part of a healthy ecosystem and provide essential protein for young birds of all species. I need to plan for a secession of berries from late spring to winter so there is food year-round for berry-eating species. I need plants that attract pollinators to ensure that my berrying shrubs produce well.
Native dogwoods, genus Cornus, are among our most valuable plants for birds. Eaten by ninety-eight species of birds, dogwood berries have a high lipid content that make them especially valuable for migrating birds. Migrating thrushes co-evolved with the Flowering Dogwood, Cornus florida. Unfortunately, because of problems with anthracnose disease, Flowering Dogwood has been too often replaced by Kousa Dogwood, which berries at the wrong time for migrating birds, if it berries at all. Ironically, Kousa Dogwood was probably the source of the anthracnose fungus. Not only do non-native plants provide sterile habitat, they too often introduce devastating fungal diseases and insect pests. Planting flowering dogwood in an area out of full sun in a more natural wooded setting helps mitigate the fungal problem. Other native dogwoods, especially the white berrying ones such as Gray Dogwood, Cornus racemose, are excellent wildlife plants.
Going native is easier said than done. The landscape and nursery industries are slow in understanding the need. When we replaced dead trees in an area that needed an evergreen buffer, we asked our landscape architect for native red cedar. He sent us a plan with a red cedar/ Chinese cedar hybrid, favored in the trade for its near perfect shape. We insisted on the native red cedar Juniperus virginiana. He replied “Oh, you want the one with the blue berries.” Yes, we want the one with the blue berries that help keep our bluebirds, waxwings, myrtle warblers, robins, and over fifty other bird species alive all winter. We want the one that is a functioning member of our ecosystem, not the one that is aesthetically pleasing but sterile. The non-native cultivar should not be more readily available and less expensive than the native plant. Consumers need to push the industry toward native.
Fortunately, there is a growing grassroots movement toward planting native, both in ecological restoration in preserves and on private property. The planting of pollinator meadows on school properties is especially heartening as it engages the younger generation. WCAS continues to support native planting through Holden Grants. We had a record number of requests for invasive species control and native plant replacement this year from grassroots groups that are improving wildlife habitat in their local preserves. If home owners will fill in the gaps between preserves by planting native, connecting corridors would form that would ultimately create a vibrant sustainable natural community.
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