Ecological Physiology

Date - 3/6/2021
Start Time: 9:10am
End Time: 10:30am
Location: UVM Centennial Woods
Temperature: ~18 degrees Fahrenheit
Wind: 10mph West
~80% cloud cover

One of the main adaptations of birds to winter that we saw in our area of Centennial Woods was the mixed species flocking in the woods. Overall it seemed most birds were hiding away from us wherever their nesting sites were, likely resting and conserving energy in the face of the winter cold. The times when we did see birds were mainly to see them feeding. When we were walking down the trail at the start of the path there would be bursts of sound from multiple species of birds, which would then peter out. Many birds would flit between the trees quickly before flying away. It seems clear that all these birds are flocking towards a food source in the tree, and that travelling together would increase each individual’s chances of finding food without as much effort spent. The more diverse a travel group is, the higher competitive advantage one has over those who are only reliant on what they know themselves.
I think it’s also possible that these mixed species groups flocked in order to find nesting cavities. Throughout the trail there were many dead snags, especially on the edges closer to the residential area, which incidentally is where we heard the brunt of the mixed species calls. The snapgs have cavities punctures into their bark, many of them that were fairly small in accordance with the snag size. At the beginning of the path near the residential areas, the snags were a good deal smaller and shallower than those deeper in the forest. Deeper in the forest the cavities got more numerous and deeper on the taller snags, around the size of tennis balls. All of the cavities tended towards the top of the tree, giving credence to the fact that birds form them for nesting purposes during the winter as a form of thermoregulation to stay out of the cold. The majority of the mixed flock flitted among areas with larger snag size and more numerous, deeper cavities. It is possible birds abandon smaller snags as the tree continues to age and decay in favor of the taller, denser newer snags.
It is also extremely possible that insect-eating (e.g. the White and Red-breasted Nuthatches we observed) and wood pecking birds are the species that utilize cavities the most often, especially with wood pecking birds physically forming the cavities themselves. There is a huge lack of insects as a food source during the winter, so cavity formations are an adaptation to staying maximizing the scarcer source of food available. Other birds species take to finding fruiting trees in place of insects, especially the Red Crossbill. The highest abundance of fruiting trees (especially crabapple trees) during the winter appeared in residential areas as opposed to the deeper forest of Centennial Woods - and that was where upwards of twenty Red Crossbills flocked. Many birds on the trail also flocked towards areas where they likely could find seeds on the ground or in the trees.
A tell-tale sign of a winter adaptation that was slowly starting to evolve back was the prevalence of the Black-capped Chickadee’s song over its call. Every once in a while we’d get a “chicka-dee-dee-dee,” but the “hey sweetie” was consistent. This was a sign that while the majority of birds were resting or feeding, slowly some species were starting to transition into their spring/summer behaviors. The Black-capped Chickadee was sending out its mating song more often than its normal call. Eventually, the mixed species flock that we came across will separate, with individual species going back to finding food and shelter and focusing their energies on breeding when the summer months come.

Julkaistu maaliskuu 8, 2021 04:22 AP. käyttäjältä