The single most important requirement for studying breeding birds is locating breeding birds to study. For the long-standing swallow project that is also being carried out here at the Ponds, this is relatively simple. The ponds at this site, and the others like it around Tompkins County, are home to several hundred nest boxes designed specifically with swallows in mind. The birds return season after season to use the nesting environment provided for them, and finding nests is simply a matter of checking all of the boxes around the sites for signs of nest construction. Out in the woods, however, things are not nearly as neat and tidy. Our target taxa build their nests on branches instead of in cavities, so they are not attracted to convenient birdhouses. Additionally, due to the exposed nature of a cup-nest in a tree, these birds make a strong effort to keep their nests well-hidden and protected from predators. This is what leads to the fundamental problem behind locating nests for study: trying to find something that the birds work very hard to make unfindable. Nests are often put in places where they are difficult to access or even see from the ground. To the prospective parents, our prying eyes are every bit as undesirable as a hungry jay or chipmunk looking for an easy meal.
Nest searching is a very contradictory practice. It can be surprisingly simple or maddeningly challenging. It requires a certain level of skill and know-how but often comes down to dumb luck. Following a bird is a delicate dance between keeping on your target at all costs but at the same time not disturbing them so much that they do not return to the nest site. Even the specific cues that indicate a nearby nest change as the season progresses. All of these factors coming together results in a potentially frustrating task that may be a turn-off to budding biologists. Those of us involved in CEFO, however, are not so easily discouraged. It all comes down to patience, persistence, and familiarity with your study subjects.
The first step towards successfully locating a bird’s nest is putting yourself in a suitable environment. Searching for tanager territories in the fields along the road to the research site is about as productive as trying to find breeding puffins along our forest trail. However, locating proper nesting territory is even more in-depth then simply looking in the right type of habitat. Birds often have specific microhabitats in which they like to nest. Grosbeaks, for example, are typically found nesting in “edge” habitats, such as interfaces between brush and trees or on the rim of clearings in the forest. Tanagers often set up shop deeper in the woods, but they seem to have a preference for branches that have a clear view of the ground below the nest. Other aspects of microhabitat include nest height, the availability of preferred building materials, and even the type of tree or shrub used. By familiarizing yourself with the specifics of where your target likes to nest, it is possible to begin the search from a proper location.
Once you’ve begun searching in a potential nesting habitat, following the birds themselves is the most surefire way to locate a nest. Simply noticing or stumbling upon the nest itself can happen, but this method is too difficult and luck-based to rely on. Singing males are the best indication of nearby territory, since all that birdsong is their way of defending their turf. Oftentimes, walking through the woods and listening for male birds can be the best way to determine where to begin the search. Find the male, and the female is usually not far away. The real goal, however, is to get visual confirmation of a bird exhibiting a behavior associated with nesting. Early in the nesting period, the most obviously visible of these is material carrying. When a female (and in some cases, a male) appears with nesting material such as twigs, grass, or lining, there can be little doubt that a nest is being constructed nearby. Later, when the chicks hatch and their are hungry mouths to feed, the parents can often be seen with beaks full of tasty insects and other food. Upon seeing either a material or food carry, the primary objective becomes to follow the bird, without losing it or spooking it, until it returns to the nest site. In Cardinalids, the female does most (if not all) of the construction, but both sexes feed the nestlings.
However, there are many times during the breeding season where things are not as simple as noticing a mouthful of sticks or caterpillars. The female begins laying her eggs shortly after nest building ends, but she does not begin to incubate them until all or most of them have been laid. If you happen upon a territory during the laying period, even if you locate the pair, finding the nest can be incredibly difficult. The female has no reason to return to the nest during this time, so she usually doesn’t. One could spend hours doggedly following a female, but so long as she isn’t incubating she will simply continue to forage and go about her own business. Once incubation starts, a different challenge arises. Both birds tend to be comparatively quiet around a nest. Short calls or soft singing may be used to keep contact between pairs or signal changes in incubation shift (for grosbeaks), but although these can be good indicators they can be difficult to pick up on. Additionally, the bird stays on the nest for longer periods of time, making fewer, shorter forays out to feed. It can be difficult to locate a female off the nest during these short trips, but fortunately if you can locate her she is likely to return to the nest quickly.
Nest searching is undoubtedly a grueling task at times, and it requires a great deal of dedication and awareness. The rewards, however, are great. Once a nest has been successfully “staked” it becomes a focal point for the study: a location where it is possible to conduct a wide range of study activities. Nests can be monitored for behavioral observations, and they are also great sites for taking photos or video. Since both parents are guaranteed to return to the nest, it can be a great spot to wait for adults to appear in order to carry out specific observations that may require following them. Construction, incubation, feeding, territoriality, and pair interactions can all be studied from a established nest site. With this in mind, it is easy to see why searching for and studying nests has become the backbone of our work here in Tompkins County.