For many animals, an adequate shelter is paramount for their successful reproduction. Here’s a sample of some of the lower Susquehanna valley’s nest builders in action…
Many of our year-round resident bird species get a head start on the breeding season as cavity nesters. Some of these mated pairs use naturally occurring hollows, while still others take advantage of the voids left vacant by the more industrious previous occupants. Woodpeckers in particular are responsible for excavating many of the cavities that are later used as homes by a variety of birds and mammals to both rear their young and provide winter shelter. Pileated Woodpeckers, like other members of the family Picidae, have an almost mystic ability to locate diseased or insect-infested trees for selection as feeding and nesting sites. In this composite image, a pair is seen already working on a potential nursery during mid-January. After use by the woodpeckers, abandoned cavities of this size can become nesting sites for a variety of animals including bees, small owls, Great Crested Flycatchers, Wood Ducks, Hooded Mergansers, and squirrels.After use as a nesting site, a void excavated by Downy Woodpeckers can be occupied in subsequent years by chickadees, titmice, nuthatches, wrens, and other cavity-dwelling species.This Muskrat (Ondatra zibethicus) with a leafy twig in tow takes advantage of spring’s new growth to construct or repair its house,……a process that can be repeated or renewed as necessary throughout the year.A Muskrat house in March. In the absence of leafy twigs, dried cattail stems will suffice. As it ages and decays, the house’s organic matter generates heat and makes an ideal location for turtles to deposit and hatch their eggs.Soon after Neotropical migrants begin arriving in the forests of the lower Susquehanna watershed, they begin constructing their nests. The majority of these species build “outdoors”, not within the confines of a tree cavity. Here we see a Wood Thrush with its bill full of dried leaves and other materials……ready to line the cup of its nest in the fork of a small understory tree.Though it often arrives during early April after spending the winter in sub-tropical and even some temperate climes, the Blue-gray Gnatcatcher must wait to start construction of its nest until many of the Neotropical migrants arrive in early May.You see, the Blue-gray Gnatcatcher relies on plenty of web-spinning spider activity to supply the construction materials it needs.A Blue-gray Gnatcatcher pulling apart a spider’s web on a warm May morning.Back at the nest site……the sticky spider webs bind together lichens and small bits of bark……to form a perfect little cup for the nesting Blue-gray Gnatcatchers.Baltimore Orioles weave one the most unique nests of any species occurring in eastern North America.Unfortunately for them, man-made litter can often seem to be the ideal material for binding the nest together. In an area only sporadically visited by anglers, this oriole had no trouble finding lots of monofilament fishing line, trash that can fatally entangle both adult and young birds of any species. If you see any fishing line at all, please pick it up and dispose of it properly.Always keep an eye open for fishing line and get it before the birds do!Like many other avians, male Brown-headed Cowbirds are now relentlessly pursuing females of their kind.All his effort is expended in an attempt to impress her and thus have a chance to mate.This male can indeed put all his energy into the courtship ritual because Brown-headed Cowbirds toil not to build a nest. They instead locate and “parasitize” the nests of a variety of other songbirds. After mating, the female will lay an egg in a host’s abode, often selecting a slightly smaller species like a Yellow Warbler or native sparrow as a suitable victim. If undetected, the egg will be incubated by the host species. Upon hatching, the larger cowbird nestling will dominate the brood, often ejecting the host’s young and/or eggs from the nest. The host parents then concentrate all their efforts to feed and fledge only the young cowbird.Watching and waiting. The Indigo Bunting evades cowbird parasitism by first recognizing the invader’s egg. They then either add a new layer of nest lining over it or they abandon the nest completely and construct a new one. Some patient buntings may delay their breeding cycle until after cowbird courting behavior ceases in coming weeks.
