Field Observation 3: Social Behavior and Phenology

DATE: March 24, 2019
TIME: 1:00 PM
WEATHER: Sunny, mostly clear blue sky. 6 °C. Winds: S 9 mph.
LOCATION: Casavant Natural Area, Winooski, VT

Birds are constantly communicating with one another through calls, songs, bright flashes of plumage, or even drumming on a tree. By far the most abundant bird I encountered today was the American Robin. These robins were being very vocal, and I noticed them mostly on the ground of the forest, probably looking for food, judging by their calls and movements. There was a decent sized group of them, about 6-8 individuals, and they were almost constantly calling to one another, as if to say, “I found some food over here!” Now that it is officially Spring, robins are gearing up for their breeding season. Their mating song is very melodic, and sounds very different from the foraging calls I heard today. They have a number of other distinct vocalizations too, each serving a different purpose (ex: alarm calls, defense calls, etc.). Robins (along with many other species of songbirds) have a fine-tuned lexicon of vocal communication.
There was one particular robin that I was able to observe on for a minute or so. This robin was hopping around on the forest floor, probably looking for insects or some fallen berries/seeds. Considering that I went on my bird walk around 1 PM, I wasn’t surprised to see this robin, and the group that it was part of, foraging. The ground is cold and frozen in the morning and at night this time of year, but the sun is at its peak in the early afternoon, and therefore the ground is as thawed out as it is going to get at this time. This would be the optimal time to forage in the dirt. It’s also possible that this was a male robin, perhaps gathering materials to bring to his mate to build a nest, though it may be a bit early in the year for this behavior, and I did not notice any mating songs.
Communication between robins also involves visual cues. Robins are fiercely territorial over their nesting sites, mates, and resources. Male robins use their red breasts to settle territorial disputes, especially during the breeding season. Dominant, older males typically have a larger area of red on their breast, which sends a visual “back off” signal to other younger males. Robins weren’t the only “red” birds I observed today. I caught a quick glimpse of a male Northern Cardinal- but a glimpse is all you need to identify these birds. The males are bright red, all over, save for a black patch around their bill. The red plumage of a cardinal serves a different purpose than the red breast of a robin. Unlike the robin, male and female cardinals are very easy to tell apart. Cardinals exhibit a classic case of sexual dimorphism- while the male is a vibrant, flamboyant red, the female has a mute brown/orange body, with touches of red at the tips of her wings and tail. The bright red plumage of the male cardinal indicates to the female that he would be a mate worthy of choosing- the pigmentation and intensity of his plumage reflects his ability to find food that is rich in proteins and carotenoids. Both the robin and the cardinal display stunning red plumage, but for entirely different reasons.

Publicado el marzo 25, 2019 12:33 MAÑANA por jessharkness2