Birding: Hatchlings, bird eggs: marauder food
By Phil KyleContributing writer
Jul 27, 2018 at 5:03 PM Jul 28, 2018 at 6:26 AM
Whether scrapes, tunnels, holes, platforms, cups, domed, woven, colonial, mud, bowers or edible, nests provide evidence that birds are the best architects in the animal world.
"Creations from spider's web, caterpillar cocoons, plant down, mud, found modern objects, human and animal hair, mosses, lichen, feathers and down, sticks and twigs — all are woven with beak and claw into a bird's best effort to protect their next generation," says Sharon Beals, a San Francisco Bay-area photographer, concerned with the environment and bird natural habitats.
Nest predation is the primary source of birds' reproductive failure on Cape Cod.
In a recent study, more than 4,200 nests all over U.S. were monitored and affected by multiple nest predators. At least 90 species were identified as nest predators (in numerous cases predators were not identified to species). Mesopredators (medium-sized mammal species including raccoons, skunks and fox, etc.) and snakes were the most common nest-predator groupings, accounting for 24 percent and 23 percent, respectively. Rodents (such as red and grey squirrels), 15 percent; raptors (hawks and owls), 14 percent; corvids (jays, crows), 9 percent; brown-headed cowbirds, 7 percent; miscellaneous predators (crabs, ants, cattle, etc.) 5 percent (Journal of Avian Biology, 2014).
Of the dozen or so snake species found on Cape Cod, only the milk snake and the very rare black rat snake qualify as nest predators. Others include grackles, jays, crows, hawks, owls, raccoons, skunks, fox, opossums, weasels, coyotes and cats.
Piping plovers' nesting success is closely monitored because of its endangered species status. As a result, the numbers are very accurate. In 2017 there were 488 plover chicks fledged on or close to the Cape and Islands. Of the pairs that didn't produce many offspring, 54 percent likely were affected by nest predation. Almost 50 percent of nest failures were because of crows or coyotes.
Nina Coleman, park manager at Sandy Neck Beach, found that a fox family secretly living under a cottage was destroying a significant portion of the piping plover chicks her staff had been guarding. Jonathan Regosin, head of the state's conservation science of endangered species program, said at the time nest predation had been on the rise.
Tern populations increased on Monomoy National Wildlife Refuge last summer (the largest common tern colony on the eastern seaboard inhabits this area). All four Cape Cod species of tern are on list of threatened bird species. Roseate are designated as endangered, while common, Arctic and least terms are species of special concern.
The nesting success of the federally endangered piping plover, on Chatham's neighboring refuge, fell below predictions. The five-year average productivity for plover chicks is .94 (ratio between pair of parents and chick survival), short of the 1.5 fledged goal, according to a report on the 2017 season.
Increased nest predation and "king" tides (extremely high), which washed over the beach and destroyed eight nests, are to blame for the low productivity.
"There's not a whole lot more we can do for plovers besides additional predator management," says refuge biologist Kate Iaquinto. "Coyotes and grackles — which have recently started breeding on the refuge — are the main plover nest predators. Four coyotes were removed by personnel from the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, who spent 40 days on the island in the spring. They also trapped grackles.
"The same predator controls will be in place this season," she adds. "One coyote can do a whole lot of damage if it gets into the tern colony."
While terns did well on Monomoy National Wildlife Refuge last summer — the refuge remains the largest common tern colony on the eastern seaboard — the number and nesting success of federally endangered piping plovers fell below expectations. American oystercatchers should also be included as beach species affected by nest predation.
The vulnerability of the high marsh species like American black duck, willet and saltmarsh sparrow, clapper rail and seaside sparrow are especially susceptible to mammalian nest predators because their habitats are easily accessed at low tides.
Although nest boxes (birdhouses) provide many common birds nesting options, they also can be primary targets for predators. The most passive way to prevent predation is to avoid placing nest boxes in areas where predators are prevalent. But, because some predators are found all over, you should consider outfitting your nest boxes with predator guards.
Year of the Bird 2018 tip: Birdhouses with any kind of predator guards were connected with improved nesting success, but nest boxes with cone-type baffles, stovepipe baffles or entrance hole extenders (wooden block-hole guards) were most likely to result in successful nesting. (Wildlife Society Bulletin 2017)
— Phil Kyle writes about birding every week for the Cape Cod Times. He is a past president of The Cape Cod Bird Club, and in his semi-retirement, works summers as head naturalist for Barnstable Harbor Ecotours. He can be reached by email at archeopt@gmail.com.