Tag Archives: Pheucticus ludovicianus

(Un)happy Endings

Even for birds, things sometimes don’t go as planned.  In fact, we’ve found that for Rose-Breasted Grosbeaks, life often doesn’t follow its intended course.  None of the Grosbeak nests we’ve found have lasted until the chicks fledged, and many were “popped” (eaten) or abandoned before the eggs even had a chance to hatch.   After six failures, but before we resigned ourselves to the apparent curse of the Pheucticus, we did a little research.  Friesen, Cadman, and MacKay found that only 46% of the Rose-Breasted Grosbeak nests they kept tabs on made it to completion, i. e. 54% of their nests did not yield any fledglings (1999).  Compared to our 0% success rate, 46% was looking pretty good.  However, Dungay, Woods, and Nichols reported a success rate of only 32% (2001).  Consultation of the Birds of North America account revealed that our Grosbeaks’ low success rate may also be a consequence of the fragmented nature of the available habitat.  Despite their preference for fringe habitats, Rose-Breasted Grosbeaks also tend to have a lower nesting success rate in more fragmented habitats.

Taking all this into account, and pushing valiantly through the heartbreak of losing yet another nest, we decided we needed to make darn sure the nest was empty.  We had assumed the happy Grosbeak couple was incubating when one or the other was constantly on the nest, which we first observed on July 2.  This meant that there should have been eggs in the nest.  To check for the presence of eggs, we used a very special piece of equipment: a nest mirror (also known as a mechanic’s mirror).

The basic plan was as follows:

Much more difficult than anticipated!

Operation Nest Mirror

Simple enough, right?  We thought so.  However, we forgot that the nest, although located relatively close to the ground, was also directly over a giant patch of honeysuckle.  After several tries, Hilary eventually managed to hold the mirror in a position that reflected the image of the tragically empty inside of the nest to Emma and me, who were looking on intently with binoculars and a camera.  Although our hard work revealed nothing but an empty nest, we felt we had accomplished something by figuring out how to look inside a nest that was way above our heads.  Hopefully the next time we use our ingenuity to look in a nest, we’ll be greeted by the sight of happy little chicks!

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Nest Searching Tales

The following are several accounts of nest finding by team member Eric Gulson.  We named the nests after the species (RBGR=Rose Breasted Grosbeak, SCTA=Scarlet Tanager) and the order in which the nests were found.

RBGR 4

Earlier in the season, we were working with several Scarlet Tanager nests and one Grosbeak nest. However, one day Cat monitored that Grosbeak nest (RBGR 1) and found that it was abandoned: no adult came during those two hours or ever again.  Because of this, finding a Grosbeak nest became a more pressing matter, and we began looking for more adults. Two days later, Jack and I were heading into the woods on the trail we take every day and I was lingering behind. As I passed a group of shagbark hickories to my right, I heard the Grosbeak call, similar to a sneaker squeaking on a basketball court. Around five meters up a pair was perched, but they immediately left and flew across the corner of a small field, a total of around 20 meters. I followed them and it seemed as though the female was collecting nesting material. She was near the ground, but disappeared momentarily behind a tree. Soon though, to my surprise, they flew back to the group of trees they came from, where the female headed straight up and towards what proved to be a nest under construction. The nest, as if to humiliate us, was over halfway done and directly above the trail. We had passed by it several days straight without taking notice. We immediately began monitoring it and by the end of the field day, it looked considerably less like a platform and had a clear bowl shape. The pair also copulated in a nearby sapling that day, and the flashing of the male’s white rump and wing patches along with its pink underwing coverts was a striking sight.

SCTA 4

One afternoon in late May I decided to stay after everybody had left, because I had my bicycle and did not depend on anybody else for a ride. It was the day after RBGR 1 had abandoned their nest, so I checked on that site before heading headed further south. Here, I heard the chck-brrr of a Scarlet Tanager, followed by two more. Four individuals, two pairs, appeared and I was clearly at their territorial boundary, since one pair stayed around in an oak tree while the other flew south. I lost track of the pair in the oak, but after a while was able to hear the other pair calling and decided to follow them. Here, I found the male in a small tree, while the female was moving around quite near the ground. She was looking around and dropped to the ground, where she hopped around several times and began pulling at something between a leaf and the floor: spider silk. She was collecting the fibers for a nest, but I quickly lost track of her when she left the floor. However, the male was always to be found in a group of small trees and I resolved to visit the next day. I did, and once again found the male in a group of trees and the female on the ground. I lost track of her until I noticed her flying into a group of basswoods, high above the ground. After watching her enter the area and loosing her four times, I finally saw the nest, twelve meters up, on the fork of a major branch. It immediately struck me how obvious its position seemed, with twelve meters of open space between it and the ground, but it still took me two days to find. I was particularly attached to this pair because the male often came quite close to us when we monitored its nest, and both individuals had distinctive patches of yellow on the head, especially the female. Unfortunately, we lost track of them once their chicks fledged.

SCTA 5

We found the nest of Scarlet Tanager 5 quite by accident. Hilary, Justin, and I had just spent hours searching for a new Rose-breasted Grosbeak nest in early June and were returning from a swamp through a different route when Justin heard a Scarlet Tanager to our north. We decided to follow it for a moment because it was near SCTA 4, although further to the east. The male was distinctive, because he had a couple of white spots on his wing, so Hilary decided to try to photograph it, and I began recording a description of its foraging movements in a microphone, trying to keep track of the bird’s every movement. As he approached a beech tree, he suddenly attacked a woodpecker that had been in its branches. Because I had seen grosbeaks and woodpeckers forage side by side, it seemed odd that the tanager would ever chase it off, so I decided that its nest might be nearby. Sure enough, a little to above and to the right of the incident there was a group of twigs and grasses, so I called Justin and kept monitoring the birds foraging behavior. As it turned out, where I was standing was the only one of four places where the nest is visible from the ground, I had been extremely lucky. It also became clear that this one and SCTA 4 were neighbors, because we would hear the males counter-singing in the mornings and were able to walk in a nearly straight line from one nest to the other.

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Spot Mapping

Spot mapping is a relatively simple but efficient method of covering an area of study during a field experiment. Requiring only a GPS and a map of the surrounding area, it allows for marking out of specific locations of interest and determination of more general regions such as territories. As such, learning the proper techniques for effective spot mapping was one of our first objectives as a group. This was true of both the local Tompkins County crew as well as the group signed on for the Borneo trip. In fact, the job fell to us to “train” the Borneo crew during the brief period they stopped in Ithaca between their respective vacations and the start of the expedition. This skill is a valuable one for field biologist everywhere, and after taking a short time to familiarize ourselves with the necessary equipment and techniques it begin our primary means of keeping tabs on our study nests.

Our TOCO crew was supplied with several GPSes for use in spot mapping. These pocket-sized devices were outfitted with a variety of options, but the feature we were most interested in was their ability to take measurements on the Universal Transverse Mercator coordinate system, commonly abbreviated as UTM. Unlike latitude and longitude, UTM measurement takes the distance from set x- and y-coordinates laid out in a grid across the earth. These measurements are referred to as easting and northing, and the GPS has a page that shows these precise measurements. A master map back at our “home base” showed the UTM grids laid out over an aerial view of our study area. This map was then scanned and copied multiple times, then split up into page-sized “zones” for use in the field. To spot map, we would take a GPS and zone maps for the sections of the woodlot we intended to visit, along with a writing implement. At any point of interest, we would simply take the last 3 digits of both measured coordinates and mark them with respect to our gridlines on the map.

This, of course, begs the question of what qualifies as a “point of interest”? The obvious answer is “a nest”, and discovering a nest is definitely grounds for a mark on the map, taking the coordinates from as close to the nest tree as possible for the sake of accuracy. However, as we’ve previously covered, nests can be difficult to find on their own. As such, we used our spot mapping trips to gradually build up an in-depth map of the region, showing us the important “who, what, when, where, and why” of our study subjects. Any observation of a target bird is denoted on the map with its four-letter band code (RBGR for Rose-breasted Grosbeak, SCTA for Scarlet Tanager, etc.). The point for marking it should be measured as accurately as possible, estimating the distance in meters and direction from the observation point to the target. A singing bird is indicated by a circle around the code, while a calling bird is underlined. If the bird is off in a direction where it is difficult to ascertain its exact location, the circle or underline are drawn dashed instead of full. Any additional notes, such as movement, behavior, individual identifiers, and sex are to be noted on the map as well. One behavior that provides us with particularly useful information is the observation of countersinging between rival males. This behavior, where two males in opposing territories sing to each other to defend their turf, indicates a clear territorial boundary. These behaviors and map observations, over time, provide us with a very clear picture of the territories and home ranges of the birds in our research area. Multiple observations on different days help us build a map of the territories these birds defend, providing us with a much more focused starting point for our nest searches.

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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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