President's Corner | Sharyn Magee
Insects are in freefall and that goes a long way in explaining our declining bird populations. Ninety-six percent of North American land birds depend on insects to feed their young. Caterpillars alone help sustain the young of over three hundred bird species. Fewer insects mean lower productivity for birds and other animals that depend upon insects. Many fish, mammal, reptile, and especially amphibian species that heavily depend on insect mass are also unsustainably declining. Insects also pollinate plants that produce the seeds and berries that many bird species need to sustain life as adults. The decline in bird numbers cannot be reversed without increasing the insect biomass.
Insects in turn depend on native plants. Non-native plants attract significantly fewer insects than native plants because insects are attracted to the plants with which they co-evolved. Oaks alone support over five hundred species of butterflies and moths. Willows, cherries, and birches support over four hundred species each. These tree species are among the best places to look for migrating warblers hungry for nutritious caterpillars.
Urban and suburban yards filled with exotic plants are food deserts for our native birds. A recent study by Narango, Tallamy, and Marra showed that Carolina Chickadees, a common species that has adapted to urban landscapes, are struggling to raise young in a landscape of exotic plants. The study showed that the chickadees could not sustain population growth where the native plant biomass was less than seventy percent. Species that are less adapted to human landscapes have an even higher requirement for native plants. Michael van Clif and I studied the plant associations used by breeding Hooded and Kentucky Warblers at Baldpate Mountain and the Sourland Ecosystem Preserve. We found that the warblers were breeding in areas with an average of eighty-two percent native plant cover, mainly Spicebush thickets, which are the best place to look for migrating Black-throated Blue Warblers that relish Spicebush Swallowtail caterpillars. Also, migrating thrushes are attracted by the lipid rich berries of the Spicebush.
Obligate insectivores like swallows and swifts are among our fastest declining bird species. Species such as Whip-poor-wills that depend on night flying insects have also significantly decreased. Decreases in insect abundance, diversity, and size has resulted in the unsustainable decline of these bird species, indicating that depletion of the bird’s food source was the main cause of the rapid decline in insectivorous birds.
Agricultural pesticides, such as neonicotinoids, called neonics, and chlorpyrifos, have been implicated in the decline of insect populations and the vertebrate species that depend upon them. A study in Germany showed significant insect population declines in preserved natural areas surrounded by farms utilizing intensive agricultural practices. Farming practices have a huge impact on insect populations. A study in Finland showed that organic livestock farming was the only mode of farming that significantly increased the population of insectivorous birds because the frequently rotated pastures used in organic livestock farms most closely resemble native grasslands. The swallow population at the St. Michael’s Farm Preserve supports this study. St. Michael’s supports healthy numbers of Tree Swallows, Barn Swallows, and Purple Martins and has a pair of Rough-winged Swallows under the Aunt Molly Road bridge.
Insecticides also have a direct effect on birds. An American Bird Conservancy study showed that a single neonic-coated seed could kill a Blue Jay sized bird. A recent Canadian study shows that non-lethal doses of neonics are having a significant effect on migrating birds by suppressing appetite. Birds exposed to neonics lose a substantial amount of weight at a time they need to be gaining weight, forcing the birds to delay migration which harms their chances to breed. Birds poisoned by neonics may not be in condition to breed once they reach their breeding grounds.
Reversing insect decline is an essential step in reversing bird decline. Fortunately, it is a step everyone can take, starting with increasing the native plant content on their own property or volunteering to plant native plants in restoration projects on preserved land. Not using insecticides and supporting local organic farms that forego insecticides would also help boost local insect populations and make migration safer for birds. The reward is outside your window.
A glorious flock of big, beautiful, raucous Scarlet Macaws inhabit the Copan Archeological site. Raised in a protected area, the macaws are not shy of people, providing excellent views of this often-elusive species, which has become very rare in Central America. These birds were rescued from smugglers as very young birds. Only young birds are suitable for the pet trade since the macaws must be acclimated to people at a young age. Adult birds are killed or driven away and the nesting trees cut down to obtain the young birds. The illegal international bird trade combined with habitat loss is the reason that so many macaw species are in serious trouble.
Stable populations in remote Amazon locations keep the Scarlet Macaw out of the IUCN Red Book of Threatened Species but the species has become very rare in Central America, resulting in a change in CITES status from Appendix III to Appendix I, highest concern, in the nine years between 1978 and 1985. While the pet trade has depressed the species, deforestation is the major reason for their decline. Since 1960, Central America has lost more than seventy percent of its forest cover. Cattle ranches, sugar cane plantations, and coffee plantations are responsible for most of the deforestation. The Scarlet Macaw has disappeared entirely from El Salvador, which is essentially deforested, and is reduced to scattered pockets of forest in the rest of Central America. The closing of the Chalillo Dam in Belize destroyed the strong hold of the Scarlet Macaws in that county by flooding one of the most pristine wildlife areas remaining in Central America.
Lack of suitable nesting holes has constrained efforts to boast macaw populations. Success with introduced nesting boxes has been mixed. Macaws are highly intelligent, social birds with a culture. Much behavior is learned, not innate. Macaws raised in nest boxes will readily use them when they reach breeding age but encouraging the first generation of birds to use the nest boxes has been problematic.
The ancient Maya considered Scarlet Macaws messengers of the Sun God, their highest deity. The fall of the Mayan civilization offers a stark lesson in conservation. Human overpopulation resulted in deforestation which resulted in water loss. Water loss led to agricultural failure, famine, and resulting discord. Eventually the civilization collapsed. Unfortunately, the cycle is repeating itself today in Central America.
The Scarlet Macaw is one of ten large macaws in three genera. Three species are listed as vulnerable, one species is endangered, one is critically endangered, one is critically endangered and possibly extinct in the wild, and one species, the Glaucous Macaw, is presumed extinct. The three remaining species are disappearing on the periphery of their ranges where they are in contact with people and are only considered not of global conservation concern because of stable populations spread out over large, remote areas of the Amazon. Protecting the remaining macaws will not be easy, but the world would be a poorer place indeed if these big, beautiful, highly intelligent birds were to disappear.—
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.