Monthly Archives: June 2012

Spotlight on: Scarlet Tanager

The Scarlet Tanager (Piranga olivacea) is arguably the bird that led to the conception of this entire project. The story begins with the Piranga tanagers, a genus that also contains familiar North American birds like the Summer (P. rubra) and Western Tanagers (P. ludoviciana) as well as more southerly species like the Flame-colored (P. bidentata) and Rose-throated Tanagers (P. roseogularis). These tanagers were originally classified with…well…the other tanagers, a wide radiation of American birds in the family Thraupidae. Recently, advances in molecular studies have indicated that this is not, in fact, the case. Piranga tanagers are not tanagers at all. According to their molecular make-up and DNA, these birds are actually Cardinalids. The American Ornithologists’ Union has since updated its taxonomy to reflect this change, placing the Scarlet Tanager and its kin alongside the cardinals, buntings, and grosbeaks of the family Cardinalidae. This discovery prompted the realization that, if these birds are so similar at their most basic building-block level, perhaps there are biological and behavioral similarities that had previously gone unnoticed. Thus, the Tompkins County branch of CEFO was born, with the goal of observing and recording the breeding biology of our own local Cardinalids.

Credit: Justin Hite

Tricky taxonomy aside, the Scarlet Tanager is a very impressive bird. They can be found in a wide range of wooded habitats across eastern North America, being replaced by the similar and appropriately-named Western Tanager in the west. They winter in northern South America, but their breeding habitat is the deciduous and mixed forests in the United States and southern Canada. The birds are about 7 inches long, with a greyish bill and feet in all plumages. Adult males have a striking pattern: brilliant red plumage with contrasting black wings and tailfeathers. The female is a dull, inconspicuous olive-green with some yellow and grey mixed in. Immatures and nonbreeding males are similar to females, though nonbreeders possess the black feathers of the breeding season. In their first spring, male tanagers may retain some yellow feathering in patches, while other males have an orange coloration overall. Fledglings often have streaking on their breast and flanks for some time after leaving the nest. The tanager is readily identified by its song, which resembles that of a robin, but with a hoarse, “burry” quality to the phrases. The bird’s “chck-brr” call is a common sound, and a distinctive identifier, in these woods.

Scarlets are birds of the canopy. Even the flashy males can be challenging to pick out as they move about the foliage in the treetops, though they can be spotted when they come into the opening or move closer to the ground. They forage as they go, gleaning insects and spiders from the leaves or snagging aerial arthropods such as dragonflies. They are also known to eat some plant matter. They usually place their nest towards the end of a branch with a clear view of the surrounding area, building a loose-looking cup of twigs and other plant materials. They seem to prefer deciduous trees, but one of our most productive nests was located in a conifer along the trail! Clutch size ranges from 1-6 greenish blue eggs with brownish speckling. Incubation lasts around 2 weeks, and the chicks themselves fledge within 9-11 days after hatching.

At our study site, we found a surprising number of Scarlet Tanager territories spread across the woods. We were able to locate and monitor 7 individual nests over the course of our field season. The birds’ distinctive vocalizations made them easy to locate, and they proved to be very cooperative subjects. The tanagers seemed to adjust readily to our presence, carrying on with their daily activities at the nest with us watching intently. Some individuals even seemed interested in us, with the pairs at nests 3 and 4 often coming down out of the canopy to watch the nest-watchers from nearby branches. We were able to observe a wide range of behaviors related to site selection, nest building, raising the eggs and chicks, and territory defense from rivals and predators. They were also much more successful than our observed grosbeak pairs at making successful nesting attempts where the chicks survived to fledge, but more on that later!

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The Art of Nest Searching

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.

Credit: Cat Lauck

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.

Credit: Cat Lauck

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.

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Introducing…TOCO CEFO

With the end of June fast approaching, the bulk of our field season here in Tompkins County is already behind us. We still have a ways to go and plenty to do before our time in the woods comes to a close, but we have seen and learned a great deal over the months. We set out for this project with a clear goal in mind: studying the breeding biology of local Cardinalids. The species found in Tompkins County include Rose-breasted Grosbeak (Pheucticus ludovicianus), Scarlet Tanager (Piranga olivacea), and of course Northern Cardinal (Cardinalis cardinalis). Our primary interest was to build a better understanding of their behavior in the breeding season with regards to interactions within pairs and between pairs, nest location and construction, care of eggs and chicks, feeding, territoriality, dispersal, and more. The behaviors of these species are of particular interest due to the recent revelation that North American Piranga tanagers are not closely related to the other tanagers in Thraupidae, but are in fact more properly placed in Cardinalidae. Our hope is that by closely studying these birds, with the benefit of knowledge that they are related, we can find similarities or traits in common that link them more closely than science initially recognized.

The woodlot located behind Cornell’s Unit 1 Research Ponds afforded us a convenient opportunity to cover a wide area of suitable habitat with relative ease. The forest proved to be especially productive, populated with many tanagers and grosbeaks defending territories across the study zone. In addition to our target taxa, there is a wide variety of other interesting birds present, including warblers, thrushes, vireos, orioles, and mimids. Our encounters with them ranged from monitoring nests or fledglings to capturing them in mist nets for banding and data processing. The media and observational data on our species of interest have painted an interesting picture of the breeding season for woodland birds here in Tompkins County. As a group, we have grown a great deal, both in understanding of our subjects and in fine-tuning of the skills required for effective field biology. Even with all we have done, the learning continues as the study period marches on. This blog will recount the discoveries, progress, adventures and misadventures of our Summer ’12 Field Season, from the very beginning of the project onward into the days to come.

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