Field Observation 2: Physiology

On March 5th from 5:00 to 6:00 pm, Jess Savage and I made field observations at the Episcopal Diocese of VT trails leading to Lone Rock Point and North Beach. This area was south of the bay where I made observations for my first field journal. The temperature was ~16°F with moderate winds from the west and snow flurries initially light but increasing. By the end of my observations, light was just at the point of being able to see the trail.

The only birds I observed were a male and female Northern Cardinal, which I heard and then saw in a dense thicket of winterberry (Ilex verticillata), birch (Betula spp.), and cherry (Prunus spp.). According to the Cornell lab's online Birds of NA, cardinals preferentially consume fruits, seeds and insects, with "bills highly adapted for extracting seeds by cutting or crushing shells." In winter they consume 88% vegetable matter (ibid.). On the basis of this information I suspect that these cardinals were feeding on Ilex berries, and that the sheltered nature of this area may have enhanced its utility as both a source of food and a way to reduce convective heat loss, esp. on a windy night like this one.

I observed the cardinals at this site at 5:24 and again at 5:54. Berries found late in the season generally have a lower caloric content, with less fat and saccharides, which allows them to be better preserved. So the cardinals' ongoing presence and apparently intense and sustained foraging behavior could be explained by their need to consume a large volume of these berries, esp. as they prepared for the demands of nighttime thermoregulation.

Because light conditions were so low on my second observation, I wonder if the brush in fact served as the cardinals' roost site. When I observed them, the male esp. was acting very territorial, making "chips," and hopping through the underbrush and into an adjacent balsam fir (Abies balsamea).

Re the snag activity: I identified seven snags of varying sizes along my route. From bark, form, and nearby species, I was able to identify two as oaks, three as cedars, and two were unidentified. I found that larger snags had more cavities with a wider variability in size and shape. Many cavities in larger trees were oblong, indicating that they were the result of Pileated Woodpecker feeding. I thumped each snag thoroughly but didn't rouse anyone from their slumber. I did not notice any correlation between the location of the cardinals and nearby snags. They were actually in a brushy area in the middle of a field, with no nearby snags.

Snags are important for so many reasons! They provide food for decomposers, which return locked carbon and nitrogen to the soil. These decomposers, both on the bark surface and within the tree itself, in turn feed many spp, including woodpeckers, nuthatches, and brown creepers. Birds ike Pileated Woodpeckers also excavate nest cavities in snags. Once abandoned, these cavities are expanded on and utilized by chickadees, kinglets, and many other species as roosts for protection and to reduce heat loss during winter.

Publicado el 18 de marzo de 2019 por