Tag Archives: Birds

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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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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