(26-03-15) “ HERBIVORES” busted preying on bird nests

Article taken from Casper Star Tribune, August 20, 1998
David Boyd
Biologists taking advantage of the latest advances in surveillance technology are recording big game animals doing some pretty wild things these days, like elk eating sage grouse eggs and white-tailed deer preying on songbird nestlings.
So what's going on in the wilds of North America? Has El Nino driven our cervids mad?
No, say biologists, these things have probably been going on a long time. Only now, with technology such as miniature video cameras allowing biologists to monitor nests, have they been able to discover and document such behavior.
"You come up with stuff that just surprises you because nobody's documented it before," says Wyoming Game and Fish chief biologist Reg Rothwell.
While probably not common, biologists say, the predaceous behavior of deer and elk is probably not that unusual, either. The animals are simply taking advantage of a quick, easy, nutritious meal.
"You think of these animals as grazers or browsers," says Rothwell, "but they occasionally eat some pretty weird stuff." Last year, for instance, a Game and Fish researcher's remote camera captured an elk eating eggs from a sage grouse nest.
"Some of these animals really are omnivorous," says Pam Pietz, a wildlife biologist at the USGS Northern Prairie Wildlife Research Center in North Dakota. Pietz likely has the first-ever photo documentation of a deer predating a bird nest. "If they come across a nest, where the food doesn't move or run away, they'll take advantage of it."
Using miniature video cameras to document the fate of grassland songbird nests, Pietz has recorded nest predations by white-tailed deer, Franklin's ground squirrels and mice in addition to the more well-known nest predators like foxes and weasels.
In two years of 24-hour-a-day nest monitoring, Pietz has documented nest depredations in 29 nests. White-tailed deer hit two nests and field mice hit three. The most common nest predators, Franklin's and thirteen-lined ground squirrels, preyed on a combined total of 13 nests. She only documented one nest being predated by a red fox, one by a weasel and two by a badger (another nest predator could only be identified as either a fox or coyote).
Biologists have known ground squirrels and deer mice can be serious nest predators, but Pietz's research may have added another rodent species to the list: jumping mice. A video of a possible jumping mouse is currently being analyzed to confirm its identity.
"Nobody's ever implicated them as possible predators of nests. They may be another group of mice that's important as a nest predator that hasn't been recognized as such."
No one has documented white-tailed deer preying on nests before either, she says. A few years ago, Canadian bird researchers capturing songbirds in mist nets reported deer eating songbirds right out of the nets. Although they also suspected the deer as nest predators, they could not confirm it.
But Pietz now has proof they are, at least in North Dakota. The deer her cameras recorded found the nests when they were grazing at night. They may have been attracted to the adult bird flushing as the deer approached. In both cases, the nests contained nestlings. But Pietz is confident that if a deer found a nest containing eggs, it would eat them too. "They don't have to be stealthy predators to take eggs out of a nest," she points out.
When she first recorded a deer eating nestlings, she wondered if they would eat eggs, too. She incorporated the help of a captive deer at the research center to find out. "We presented it with a few quail eggs -- just to see what it would do -- and it munched them right up."
It's not too surprising that a variety of animals would be interested in nest contents, says Rothwell. "There's certainly some nutritional value."
Indeed, by necessity bird eggs are one of nature's most complete nutritional packages. Unlike fish and amphibian eggs, birds and reptiles hatch when they are nearly fully developed (as opposed to hatching into a larval form, like a tadpole).
But since bird and reptile embryos develop outside the body of a female (unlike most mammals), their eggs must provide them with all the nutrients necessary to fully develop.
To meet the demand of a growing embryo, eggs provide high quality protein (containing all the amino acids), as well as fats, lots of vitamins including A, D, and E, and scores of minerals like calcium and zinc.
And nestlings are a good source of protein, fats and other nutrients.
So how big a deal is this ungulate nest predation? Should we blame low numbers of sage grouse or dropping numbers of grassland songbirds on elk or deer?
Rothwell says that these predations probably occur only occasionally and are nothing to worry about. "It's not a huge problem, and it's probably been going on for eons."
To find out more about the Pietz study, visit (http://biology.usgs.gov/news/98-011.htm) on the Internet.

Sources: http://www.npwrc.usgs.gov/news/press/ontape.htm
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