Field Journal 3

Field Journal 3: Ecological Physiology
March 8, 2021
Start time: 9:03
End time: 10:42
Location: Centennial Woods, Burlington, VT
Weather: 19 degrees F, 10-20% cloud cover, NNW wind at 3 mph
Habitats: forested areas, including pine, deciduous, and border near aquatic habitat

Birds, at the moment, are trying to limit the amount of energy being spent in response to the limited availability of food. In order to do this, their activity will be reduced. Resting and sleeping will increase, while behaviors such as singing, which is very energy consuming, will dramatically decrease. As the cold temperatures and harsh weather conditions make survival difficult for many organisms, birds must adapt their diet to allow them to take advantage of any available nutrients. Species such as White and Red-breasted Nuthatch will peck under the bark of trees in search of dormant insects overwintering. Robins were observed near crabapple trees, where they can feed on the dried fruits. Crossbills use their uniquely adapted beaks to pry open pine cones and access the seeds. Other species of birds utilize a caching technique. Black-capped Chickadees will quickly gather large amounts of seeds at one time, and store them away to access later. Species will utilize any human-given food sources as well, such as bird feeders and suet blocks that provide essential fats and energy to help get them through the winter.

In the harsh cold of winter, birds have a number of different behavioral and physiological mechanisms that are used to maintain a warm body temperature. In my own observations, I observed a behavioral technique, where a male Northern Cardinal had his feathers fluffed up to create extra air pockets. This action retains heat and creates an extra form of insulation for the bird. Some species of songbirds utilize the warmer, microhabitat found in tree cavities, and they often utilize huddling as well to shield from the elements and generate more trapped heat. Apteria are areas of a bird where no feathers grow, resulting in large quantities of heat to be lost from them. The most prominent ones we can observe are the feet. To keep these areas warm, some species will tuck their legs under their insulated wings, either from standing on one leg, or laying on their sternum.

Species such as Tufted Titmice and Black-capped Chickadees prefer to overnight inside the hollows made in snags. This allows for enhanced thermoregulation during harsh temperatures. Multiple individuals of these species will tend to huddle together within the cavities to increase the amount of heat generated. Dense vegetation also provides a welcoming area to overnight for many songbirds, providing them with some insulation, shelter, and protection from predators.

Mini activity:

Over the course of my experience I was able to identify a total of 14 snags near the trail through Centennial Woods. Each snag was primarily made from a once living White Pine tree, and contained anywhere from 3 to 18 cavities created by birds. It was seen that there were often more rounded, smaller cavities present in regards to only a few large rectangular ones. This illustrates that Downy or Hairy Woodpeckers may either be more present than Pileated Woodpeckers in the area, or that Pileated Woodpeckers rely on snags less than the other aforementioned species. There was also a distinctive relationship between snag size and cavity abundance. The smaller the size of the snag, the less cavities were present. This may likely be due to the time the snag has existed within the forest. Over time, the snag may have decomposed and disintegrated more, causing more insects to feed, and therefore an increased bird presence on that snag compared to a taller one. This trend was also observed in cavity size, where the cavities were larger in the short snags. This may similarly be as a result of time, or perhaps species presence. If these larger cavities were created solely by Pileated woodpeckers, we can note a relationship between smaller snag sizes and an increased Pileated Woodpecker preference. However, these larger cavities may be as a result of repeated use over time. Species such as squirrels and chickadees often enlarge cavities created by woodpeckers in an effort to access other parts of the snag or create a viable shelter for overnighting. This would be evident in the smaller snags as they are most likely a bit older than the others, allowing more time for cavities to be made and then widened in the future.

Tapping on any of the snags unfortunately did not result in any bird sightings from inside. However, during observations, a White-breasted Nuthatch was seen inside a natural cavity at the top of a snag produced from a decaying pine tree. It was seen rummaging through leaf matter, perhaps in search of insects for food. A Red-breasted Nuthatch was also observed on a broken branch protruding from a snag. It appeared to also be foraging for insects, but underneath bark instead. Although these individuals were not observed within the snag cavities themselves, it is important to reflect on how different species can benefit from the presence of snags and their variable functions. We can see that snags provide a welcoming shelter for many species looking to overnight and avoid harsh weather conditions and predators. These cavities can also serve as nesting locations for many songbirds as well during the breeding season. Black-capped Chickadees and Tufted Titmice are primary species that use snags for shelter, but sparrows, finches, and other small song birds also utilize these spaces for the same reason. As observed, snags can also provide a great habitat for insects, and therefore great food sources for many different species of birds. Holes present throughout all snags, both circular and rectangular, are clear evidence of woodpecker activity from a range of species. Both species of nuthatch were observed foraging along the surface of the snags as well, confirming the importance of snags as a potential food source. Other species within the ecosystem also benefit from snags, where squirrels will utilize woodpecker cavities, and the decaying wood will provide a habitat for many insects and fungal species.

Posted on March 8, 2021 09:37 PM by acshiers