Tag Archives: Activities

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!

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(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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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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