It’s July 21, early Friday morning, as I write this week’s column. We had a wonderful ¾ inch of rain last night, but it came with strong wind gusts. The five baby bluebirds were safe in their nest box when I checked on them. They should be ready to take wing and join their older brother and sisters in the big outside world next week. Four baby barn swallows fledged last week from their nest on a platform above our garage door. We enjoyed three successful robin nests on nesting platforms I built under the eves of the house earlier in the nesting season, too. I assumed that robins were still nesting because I had seen the adults carrying food. The nest platforms were empty, so the new nest was in one of the trees. I wasn’t sure where until this morning when I found three half-grown baby robins dead on my driveway. It took some searching, but the nest was soon found, well-hidden in leaves near the end of a branch in the top of our lilac tree. Last night’s wind shook the branches so hard that the little ones were tossed out.
Birds have a great deal to consider when they select a site for their nest. First of all, the habitat has to be right. The nesting territory that a bird selects must supply all of the family’s food and water needs and provide suitable sites for a safe nest. The various foods must be present at the right times, too. Most species require insects to feed their young, even though some adult birds eat primarily seeds. Some birds eat only flying insects. Others eat mostly caterpillars, and yet others primarily worms. Each bird has its own unique combination of food, water and nesting site preferences. The habitat has to be diverse if it is to support several species.
Tree leaves hadn’t fully formed to provide hiding cover when those early-nesting robins began their nest building in the spring. The nest platforms under the eves of my house were a good sheltered alternative. They provide nearly perfect cover from spring storms, but are easy to find for birds like blue jays that raid robin nests for their nutritious eggs. Jays weren’t around this year, but they have typically stolen the eggs from at least one of those early robin nests each year. Once the trees leaf out, they provide better hiding places for robin nests. Though well hidden, the branch-end nest proved to be a poor choice for weathering a gusty storm.
Ground-nesting birds have other things to consider. Most prefer good overhead cover to screen their nests from aerial predators, but some, like killdeers, like nothing better than an open, gravely surface where their eggs look just like the rocks they’re sitting on. Gravel roads and parking lots look great until car tires roll over their nests. Ground nesters need access to water, too, but it can become their enemy in a storm. Low sites like ditch bottoms, waterways, or poorly drained pockets can flood during heavy storms, and even a few hours of flooding is enough to chill eggs or young birds to death. Ditches and waterways are known as linear cover. It’s often the only permanent vegetation that’s left in our heavily agricultural landscape. Pheasants, meadow larks and other ground-nesting species therefore have little choice but to nest there. Though cover over the nest may be good, there isn’t much of it, and nest predators like coons, skunks, cats and foxes have little difficulty in finding nests in such narrow strips of habitat. Waterfowl must have access to water, as you might expect, but local nesting ducks, like mallards and blue-winged teal, nest in grasslands that are often well away from the nearest water. Any nest in a narrow fringe of grass around a pond is almost certain to be lost to a predator.
Larger blocks of nesting cover like hay fields can be attractive nest sites for a variety of species. They are large enough to make it more difficult for predators to find the nests. Hay field nests face another threat, though. It takes a month to six weeks for birds to initiate a nest, incubate the eggs and (at least for songbirds) raise the young to a point where they’re able to leave the nest site. The birds may avoid predators and survive storms, but if the hay mower arrives before the young can get out of the way, all is lost.
It’s not easy being a wild creature, even in good habitat. I was sad to find those poor little storm-tossed robins this morning, but I wasn’t surprised. I wasn’t surprised, either, when I saw two very overworked little chipping sparrows feeding a single baby cowbird that was more than twice their size. Their nest was a failure as far as reproducing chipping sparrows goes, but there is no hiding from a nest parasite cowbird, no matter where the nest is built.
Steve Lekwa is a former director of Story County Conservation.