Flight Lines: Real nature often harsh, not always happily-ever-after
Early one morning last week I walked up the steps of a neighbor's house. Out of the corner of my eye I noticed movement. A moment later there was an explosion of sorts. Three or four young American robins fluttered out of a nest atop the porch light and scattered in every direction. Barely feathered, this was obviously their first excursion out of the nest. Life, from this point on, will get no easier for these birds than it was while snuggled in the care of doting parents.
Most folks from my generation remember well the Walt Disney show which used to air on Sunday nights. Quite often, animals would be a featured theme. As I recall the show, with the benefit of age and experience, it was pretty sanitized. The harshness and cold indifference of nature was whitewashed into tame fairytale versions of reality. Now that I think about it, most shows were like that then. But it left with us the misleading impression that all creatures lived in a sort of harmonious existence where "happily ever after" reigned. The truth, as it is said, is something different.
One area which has received quite a bit of study among birds is nest success. For waterfowl, success is defined as the moment young leave the nest. Often expressed as a percentage, these are numbers which come as a big surprise to most people. "It's not as high as some might think," said Larry Igl, Ecologist at the Northern Prairie Wildlife Research Center in Jamestown.
I found a study (Greenwood, Sargeant, Johnson, Cowardin, Shaffer, 1995) which looked at the nest success of five common duck species in a portion of the prairie pothole region of Canada. From the abstract: "We detected no significant difference in nest success among species: mallard (11%), gadwall (14%), blue-winged teal (15%), northern shoveler (12%), and northern pintail (7%). Annual nest success (pooled by study area and averaged over all study areas) was 17% in 1982, 15% in 1983, 7% in 1984, and 14% in 1985." Not great odds.
What stands in the way? Predators mostly. Greenwood and his colleagues "estimated that predators destroyed 72% of mallard, gadwall, blue-winged teal, and northern shoveler nests and 65% of northern pintail nests."
The list of perpetrators is long. Just about every critter walking, skulking, crawling or flying will feed on one another, and nests with eggs or young represent a ripe target along with brooding parents. "Striped skunk, red fox, raccoon, coyotes, mink, and even Franklin's ground squirrel are just a few," said Igl. "A lot of these mammals are opportunistic feeders and find eggs or young a quick protein meal."
It's really no easier for songbirds. Igl said, "There is a larger suite of predators with passerines (songbirds) than there is with waterfowl; smaller predators such as mice, 13-lined ground squirrels and snakes also will depredate songbird nests. In the forested areas of the Red River Valley, red squirrels may be a major predator on songbird nests."
While predation is the major cause of nest failure among birds, it isn't the only factor. Habitat is likely second on the list. The amount and quality of cover along with the state of the local predator population plays into this, along with location. "Some areas, such as islands, provide a fairly safe location for waterfowl to nest, and nest success may be considerably higher on islands than elsewhere," said Igl.
Weather is another major influence. The cold, wet weather we experienced the first two weeks of May likely took a major toll on local early nesters.
Given all this, one would think we'd be running out of birds by now but that's obviously not the case. Nature has a way of absorbing losses and compensating for them. With most birds the answer is numbers, lots and lots of numbers. Nature factors in losses in any given year so most populations produce many more eggs than is needed to sustain them, often by re-nesting. "Upland-nesting waterfowl and grassland birds have a strong propensity to re-nest," said Igl. "Some will re-nest multiple times, giving them more than one chance to be successful."
The robins I saw bursting from the nest the other day are not even close to making it yet. The rough-and-tumble world of the animals is fraught with pitfalls and peril.
It's a choreography of survival and loss. I've used this borrowed phrase many times but it fits yet again, "Life in the wild is seldom mild."
Corliss is a West Fargo resident, avid birder, and ND Game and Fish volunteer instructor. He serves as a corporate pilot for Forum Communications. firstname.lastname@example.org.