Pennsylvania Game Commission: Nature vs. Bluebirds: 5-0

Wet spring rough on many wild birds and mammals

HARRISBURG, Pa., May 27, 2011 /PRNewswire-USNewswire/ -- In an unfortunate turn of events, the first nesting attempt for bluebirds behind the Pennsylvania Game Commission's Harrisburg headquarters appears to have lost out to nature. What made this loss different from most is that it all played out in full view of those who tuned into the Game Commission's website (www.pgc.state.pa.us).

Earlier this year, a pair of bluebirds had successfully nested and laid five eggs. While only four were visible at first, after some readjustments of the camera lens, all five eggs were visible.  

"The first set back for this nest was when only two of the five eggs hatched," said Doug Gross, Game Commission ornithologist.  "While it is not usual for an egg or two of a clutch to fail to hatch, having three fail to hatch appears to have been a harbinger of bad luck for this nest.

"We don't know what happened to claim the pair of chicks that did hatch, and we can only speculate. It is possible that one or both adults died. Wet weather makes it difficult for adults to find food and feed young. They have to wander farther to find food, making them vulnerable to predation or other kinds of mortality, such as getting hit by a car. The more you have to wander around, the more likely something will get you."

While there is a strong possibility that the adult bluebird pair may attempt to re-nest, Gross and other Game Commission biologists talked about how, in a larger sense, the excessively wet spring has been difficult for many kinds of birds and mammals. 

"Most songbirds, including bluebirds, forage on insects during the nesting season," Gross said. "When it is raining regularly, they have greater difficulty finding adequate amounts of food for their young. The nestlings are very demanding of food, requiring several visits each day. The very young nestlings also are poorly insulated with natal down, so prolonged absences by the adults mean that they are unprotected from the cold, often dying of exposure if not starvation.  

"If the adults are away longer, the nests and their contents are more vulnerable to predation from domestic cats left to run free, as well as wildlife predators, such as raccoons, skunks, chipmunks, squirrels, opossums, snakes, crows, ravens, jays and hawks."

Gross also noted that ground-nesting birds are particularly vulnerable because hard rains and run-off can literally drown the exposed eggs or young.  

"Birds that nest along streams, including embankments, can have their nests flooded," Gross said. "Belted kingfishers, northern rough-winged swallows, and bank swallows are among the species that nest right in stream banks. In the deep woods, several songbirds nest in roots and on the ground near streams including Louisiana waterthrush and winter wren. 

"Large stick nests of some of our raptors are vulnerable to getting soaked and weighing down their supporting tree or snag. Some bald eagle nest trees have been washed away by flood waters this spring. High muddy waters make it more difficult for visual predators, like bald eagles and ospreys, to find their food, causing them to range farther from the nest to provide adequate food for their young. Some raptor nestlings starve when their parents cannot hunt prey during bad weather." 

Mary Jo Casalena, Game Commission wild turkey biologist, said wild turkey nests may be impacted from this wet spring, too.

"Some researchers call it the 'wet hen' theory, in which hen turkeys incubating their nests must tough it out during rain events and get wet," Casalena said. "Wet hens emit more odor than normal, so mammalian predators, with their keen olfactory sense, can more easily locate these 'smelly' hens, and either cause the hen to abandon their nest, or actually kill them on the nest. Keep in mind that, being a ground-nester, predation to nests normally is high and hens are most vulnerable to mortality during nesting season.

"To compensate, wild turkeys are able to re-nest and can lay two complete clutches with one successful breeding by a male turkey."

John Dunn, Game Commission Game Management Division chief, noted that cavity-nesting wood ducks, common mergansers, and hooded mergansers can have their homes washed away or flooded by high waters.  

"Game birds can re-nest if losses occur to nests or young, but second clutch sizes are always lower and nesting success is reduced compared to first nests," Dunn said. "Cold springs accompanied by wet weather have a bigger impact than just high precipitation. Since the peak of hatch is late May early June for turkeys, grouse and pheasants, the weather we have the next couple of weeks will be more important than what occurred earlier.

"While we still are compiling the results from the annual waterfowl breeding survey, it appears the number of Canada goose nests and broods were down as a result of nest loss from extreme flooding along streams and rivers this year. Mallard numbers also seem to be down somewhat.  There will be a renesting effort, but it likely will not be as productive as first nest attempts."

Ground-nesting mammals, such as cottontail rabbits, also are affected by extremely wet conditions.

"Cottontails construct a nest at the bottom of a slanted hole about seven inches below the ground surface," said Tom Hardisky, Game Commission game mammal biologist. "Newborns are left unattended by the adult female, except for periodic feeding, until the young leave the nest at about two weeks of age. Cottontail litters rely on body heat from one another and are particularly vulnerable to flooding rain and high water tables.  Females will re-nest if a litter is lost.

"Most mammals that reproduce in a den will move their newborns to a drier site. However, many species of small mammals, as well as most rodents, nest on or below ground level. Some aquatic rodents in stream habitats, such as muskrats, are very susceptible to mortality from sudden water level rises. Muskrat burrows that quickly fill with water can entrap adults and their young, causing them to drown. Prolonged flooding will displace surviving muskrats to new areas, where they may experience food scarcity, greater exposure to disease, or increased predation."

"Most carnivores utilize protective dens to rear their young and are less affected by wet weather," said Dr. Matthew Lovallo, Game Commission Game Mammal Section supervisor. "Smaller mammals are more likely to experience increased mortality due to cold temperatures and excessive precipitation."

Calvin DuBrock, Game Commission Bureau of Wildlife Management director, noted that the bottom line is that weather-related phenomena can definitely be tough on wildlife in the short term, but should be kept in perspective.

"As long as overall populations are healthy and adequate habitat is maintained on the landscape, there's little cause for concern about long-term effects," DuBrock said. "Pennsylvania's birds and mammals have demonstrated their resilience to wet weather, extreme drought, and harsh winters in the past, so there is every reason to believe that despite whatever increased mortality or decreased reproduction they experience this spring, they'll soon bounce back as strong as ever."

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SOURCE Pennsylvania Game Commission