Journal archives for March 2019

March 18, 2019

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.

Posted on March 18, 2019 17:42 by sam_blair sam_blair | 4 observations | 0 comments | Leave a comment

March 23, 2019

Field Observation 3: Social Behavior and Phenology

I walked a ~ two mile loop in Centennial Woods on Saturday, 3/23 from 1:30 to 2:45. The weather was fair, with light-moderate winds, 50% cloud cover, and temperatures around 32° F. It was snowing in the mountains, and there was ~3 inches of fresh wet snow on the ground and clinging to tree limbs in the woods.

I heard BCCH making contact calls (high-pitched chips) and some love songs (chee-dee, chee-dee). I also heard a few territorial calls (chick-a-dee-dee-dee). The contact calls seemed to be a sort of "background noise," accompanying feeding and movement through the canopy of a stand of mature pines. The territorial calls and some louder chips were heard when I "pshh"ed in the vicinity of this small flock. I believe this sound works because it could represent a range of animals' alarm calls. It sounds kind of like a chipmunk or squirrel that is irritated about something. Small birds listen to one another and to other animals in their environment to detect danger or things out of the ordinary. This sound seems to replicate that type of cue, which explains why it can be met either with increased interest or a rapid departure from the area, depending on how it is perceived.

I noticed that contact calls generally accompanied movement from one foraging site to another, and that this movement sometimes seemed to involve wing flares that were more flashy than would simply be necessary for changing feeding location - this suggests to me that what I heard as "contact calls" can also serve an assertive function in establishing dominance hierarchies at food resources. Another sound that seems to serve a communication function was the drumming of a Pileated Woodpecker, which I heard at a distance but was still loud and clear. It must have found a good hollow tree to use as a drum. This sound communicates territoriality, which makes sense given the time of year, when birds are generally beginning to establish breeding and feeding territories.

A small Brown Creeper I observed made very high pitched, single notes (tseee, tseee). I thought I heard another individual responding, which suggests to me that these calls served a contact function. The Brown Creeper's foraging behavior involved frequent movement among small and medium sized trees, on which it spiraled up the trunk, apparently feeding on something in the bark. I did not quantify the intensity of this feeding, but it seemed somewhat desultory, especially given how much of the bird's time was spent calling and moving as opposed to feeding (about 2:1). I frequently saw the Brown Creeper in the same area of a tree as a BCCH, but they seemed to effectively partition the resource by utilizing different parts of the tree - the Brown Creeper stayed on the trunk, while the BCCH stayed on smaller side branches.

The behaviors observed in the Brown Creeper make sense given both the time of day and the time of year. In early afternoon on a bright, somewhat warm spring day, the Brown Creeper has presumably reached a positive energy balance and is now foraging to build up stores for night time. However, given the relatively mild weather and the length of the day now that we are past the equinox, it makes sense that the individual observed was using its time to move and call more than it was to feed. This has to do with the time of year - early spring - which in many passeriformes is a time for establishing beginning to attract mates and establish dominance hierarchies and breeding territories. Perhaps this Brown Creeper was starting to allocate more energy towards these activities, while still needing to feed enough to fuel its metabolism and begin to build stores for the energetically expensive business of mating that is soon to come. I will also note that at this point in the season, many of the most easily available overwintering insects and spiders found in tree bark may have been consumed, while the emergence of insects from their overwintering stage has likely yet to begin. So this is in all likelihood a time of some scarcity for the Brown Creeper - its frequent movement and its somewhat unfocused feeding may simply have been a reflection of food scarcity.

Two different plumages I observed were that of the Brown Creeper and the male Northern Cardinal. The brown creeper has a mottled brown and black pattern on its back. When it moves up the bark of a tree, it blends in so effectively that you can't even see it unless it's moving. This plumage is highly adaptive as a form of camouflage in the bird's feeding environment. It's also hard not to notice the pure white of its belly, especially when it flies. Perhaps this white is flashy enough to serve as a signal of attractiveness, and its location on the belly makes sense in this case because it is only visible when the bird is in flight (i.e. not foraging, when it wants to remain invisible). This plumage contrasts sharply with that of the male Northern Cardinal, which is about as conspicuous as could be. The bright red of the cardinal's feathers must serve as a mating cue, and certainly makes no effort to hide. Instead, in the dead of winter when nature is purely in shades of black, white, and brown, this red stands out like a sore thumb and must be associated with an early breeding/mate attracting season. It requires carotenoids from winter berries to maintain, so it serves a double function in that it makes creative use of a well-preserved winter food resource to indicate relative fitness.

Posted on March 23, 2019 19:46 by sam_blair sam_blair | 8 observations | 0 comments | Leave a comment