Category Archives: Birds

Our target taxa, and other avians of interest

Aerial Mist Netting: Necessity is the Mother of Invention

Another crucial skill for field ornithologists is being familiar with mist netting and bird banding. Stringing up mist nets is often the most effective way to capture birds, especially when used in conjunction with audio playback to draw in potential targets. The nets are usually placed between two trees or poles, creating a nearly invisible barrier for unsuspecting birds to fly into. They then become tangled in the finely-woven web, allowing for the biologists to step in and carefully remove them. Birds can be caught in this way for any number of processing procedures, including banding, physical measurements, and collection of blood or feather samples. They can also be turned into specimens.

Our Cardinalid project here in Tompkins County did not specifically require any data from netted birds. Our focus for this season was primarily on behavioral ecology, which can be observed in the bird’s natural setting. However, we still recognized our study site as a great location for learning the basics of mist netting. More importantly, it was imperative that the Borneo crew be well-versed in proper net set-up and bird handling, as much of the information they hoped to obtain in Tawau was dependent on the capture of individual birds. However, there was an additional snag that came along with this need: many of the target Bornean birds live at higher levels in the forest foliage. While mist nets are typically placed on the ground and extend as high as the poles they attach to, a significant number of the target taxa for Tawau are primarily birds of the canopy. As such, we were faced with the challenge of not only refining our basic net and bird handling skills, but also trying to come up with a way to catch higher-flying species.

The answer to this problem turned out to be surprisingly simple, largely thanks to the ingenuity of crew member Justin Hite. Using the tools at our disposal, we were able to design and construct an elegant and efficient means of placing nets at greater heights than usually possible. To begin, a “backbone” of p-cord was strung between two trees at the desired vertical level for the nets to hang from. This was achieved either by throwing the ends of the rope or using the large-size slingshots provided for us by the Cornell Outdoor Education department (COE). Next, full loops of p-cord were then attached to the “backbone” at either end. These loops were large enough to run from the ground up to the line, and they were fastened in such a way that they held their position horizontally while still maintaining the freedom to move in a continuous loop. Lengths of PVC pipe (with holes punched in them for attachment of mist net trammels) were then tied to these loops so they could easily be brought down to ground level or run up to full height. The ends of these loops would be tied to nearby trees to keep the nets taught, but could easily be undone to lower them on command. Once the nets were strung between these pipes, the system was ready for operation.

We set up several “net backbones” at various heights in different locations of interest. Our on-the-spot solution to a very important problem proved more effective than we ever expected. We caught a wide variety of species in our nets over the weeks, including Ovenbirds, titmice, and various thrushes. This allowed us the chance to practice extracting birds from the netting and processing them for data and banding. What’s more, our system was found to be surprisingly efficient even when capturing birds in the treetops. The total time it took from a bird hitting the net to returning the emptied net to position was only about 2 minutes. Mind you, that includes getting to the net, freeing the loops, lowering the PVC pipes and net, extracting the bird and placing it in a bird bag, running the nets back up, tying them off, and returning to the banding station! Not bad for a morning’s worth of crafting.

We can only hope the system we devised has been equally effective for our colleagues in Borneo!

Advertisements

Leave a comment

Filed under Birds

(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!

1 Comment

Filed under Birds

What Could be Better than Ice Cream?

Two Fridays ago, our research team headed into the field, eagerly anticipating the prospect of Purity ice cream at the Lab of Ornithology’s social that afternoon. Little did we know that we were in for a very different (and as much as we love Purity ice cream), even better, treat.

Opening up what we’ve termed our “nest contents” spreadsheet in Excel, we briefly scanned our timeline to gauge the approximate time of hatching for our only active Scarlet Tanager (Piranga olivacea) nest at the time. The Scarlet Tanager account on BNA (the Birds of North America Online) describes departure from the nest on day 9 or 10 after hatching; by our rough calculations, the fledglings at our nest of focus would either be near the nest, already out and begging for food, or in the nest, close to fluttering out. With that in mind, Jen and I decided to head out for a two-hour nest watch, lugging – just in case – the HDV camera lent to our team by Macaulay.

While Eric and Tim went in search of new nests and juveniles, the two of us settled down in a spot where we could get a clear view of the nest (SCTA5 is notorious for being extremely well-hidden). After focusing the video camera on the delicate, saucer-shaped nest far above our heads, we started the watch. The first 30 minutes or so were much like any other day of nest watching involving parental care of nestlings – one parent at a time arrived to the nest at varying time intervals – the only exception, however, was that within that first half hour at SCTA5, only the male visited the nest.

For a brief (and of course, always exciting!) snapshot of our nest watch that day:

At 10:55 AM, as the parents were out foraging, there was some slight movement on the nest.
At 11:01 AM, the male was singing softly as the female called in the under-story, on a branch remarkably close to the observer – both aspects being atypical for the behavior of a female tanager while foraging for her nestlings.
For the next five minutes, the female gradually moved closer and closer to the forest floor directly below the nest, continuously chck-brrring.
At 11:05 AM, sounds that seemed to be begging calls were heard. The male and female continued to sing and call until suddenly, there was a small flash of a fluffy grey bundle scurrying towards a log.

Yes, indeed – it was a Scarlet Tanager fledging, our first one seen straight out of the nest.

The HDV camera Jen and I had luckily brought out was quickly trained on the fledgling, who was remarkably agile. He was able to make his way across the forest floor fairly quickly and was capable of short, fluttery flights. As Jen and I followed him from one log to another, he eventually tried to move up along a small sapling – an evolutionarily helpful instinct for avoiding predators.

Scarlet Tanager Fledgling

Hello, world!

As we were wholly engrossed in our careful stalking of the fledging, we almost forgot to call Tim and Eric to join us. When they finally arrived, armed with a Marantz audio recorder, an extra battery for the camera, and an additional tape for the video camera, our small but extremely excited fan club for the fledging was complete.

Eric Gulson taking an audio recording of begging calls.

Our team spent the next five hours collecting digital media on the fledging, who finally decided to stay on a thin sapling branch (which oscillated up and down every time the male tanager came in to feed his fledgling, leading to some adjustments with the video camera). In the course of those five hours (time does fly when you have a fledgling to occupy your thoughts), Eric found another young Scarlet Tanager fledgling about 6 meters up a maple. This second fledgling was being fed by the female in the territory, indicative of a rather common practice among parent birds of splitting up feeding duties among their fledged young.

Jen Goforth recording a video of the fledgling.

At the end of the field day, we reluctantly left the SCTA5 territory and headed back to the data trailer with our photos, videos, audio recordings, and of course,  some lasting memories – perhaps not of ice cream, but certainly of a very endearing fledgling.

1 Comment

Filed under Birds

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.

Leave a comment

Filed under Birds

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.

Leave a comment

Filed under Birds

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!

Leave a comment

Filed under Birds