FJ3: FIELD OBSERVATION: Ecological Physiology
FJ3: FIELD OBSERVATION: Ecological Physiology
Date: February 23, 2021
Observation Period: 2:20 p.m. - 3:40 p.m. (1 hour 20 minutes)
Location: Gilbrook Natural Area, Winooski, VT, 1.82 miles
Weather: 31 degrees, Partly Cloudy, Wind-3 mph SSW
Habitat: Walking trail adjoining residential and college campus area through mixed woods, mainly oak and birch, with a large reservoir and two ponds.
I chose Gilbrook Natural Area for this walk because I thought it would provide good habitat for snag watch, which it did, however, there were very few birds. In one area where a little stream was flowing a mixed flock of two Black-capped Chickadees, two Tufted Titmice and one White-breasted Nuthatch were darting around the trees in search of food. I saw one Tufted Titmouse collect a red berry, fly to a nearby tree branch and break it open to eat. The feathers on the Black-capped Chickadees were noticeably fluffed up. At one point along the trail, five American Robins flew by and landed in a tree outside the park boundary. I saw three American Crows flying together overhead.
With over 150 days when nighttime temperatures in the Burlington area fall below freezing, birds who spend the winter here have evolved and are adapted to survive the environmental conditions. Daily activity involves searching for food and trying to keep warm.
A bird's digestive tract is specialized for diets that change seasonally. They must eat more in fall and winter to build up body fat. When food is scarce in winter, birds may forage most of the day. They may supplement natural food sources such as nuts, seeds, fruit and insects with food from bird feeders and seek unfrozen water sources. Cedar Waxwings supplement berries with catkins. Some birds like Black-capped Chickadees, Tufted Titmice and White-breasted Nuthatches gather in mixed flocks in search of food. These birds cache food for later use. The birds at Gilbrook Natural Area have access to bird feeders in the adjoining neighborhood.
Birds have evolved with feathers that provide insulation and the ability to increase aerobic metabolism which allows them to regulate their body temperature for warmth. Small birds lose heat faster than large birds, but some birds like house sparrows molt into thicker plumage. A bird's contour feathers contribute to insulation, but the down feathers underneath are the primary sources of insulation. Birds can change their feather positions by fluffing out their feathers to create air pockets to trap body heat for added insulation. I noticed this on the Black-capped Chickadees. Another technique we may notice, especially with ducks, gulls or herons, is that a bird may stand on one leg and the other is tucked under the body or their bill is tucked under the wing feathers for warmth. Birds can also waterproof their feathers with oils from the uropygial gland, and this will provide insulation to the barbules in their feathers.
Birds have high body temperatures of around 105 degrees F and a high demand in winter for them to regulate their body temperature to conserve energy. Black-capped Chickadees put on extra fat in winter and will fatten up during the day, then burn off fat during the night to produce heat. They have evolved to conserve their energy reserves by lowering their body temperature at night in a condition called facultative hypothermia. Gulls and ducks have a countercurrent blood exchange system that regulates the rate of heat loss in their feet and legs to prevent them from freezing. Shivering is a short-term response birds may use to generate heat, however, tensing its muscles to do this requires more energy. When resting, birds may position themselves to take advantage of heat from the sun or shelter from the wind.
Birds have different strategies for finding shelter to provide warmth and cope with winter nighttime temperatures. Crows and European Starlings roost communally for warmth and protection. Microclimates create a warmer place that will reduce the rate of heat loss. Grouse and Common Redpolls can burrow into the snow for warmth. Conifers also provide a protected place for birds to spend the night. Birds such as Black-capped Chickadees, White-breasted Nuthatches and Tufted Titmice may join together and seek shelter in tree cavities.
Snag Watch:
Gilbrook Natural Area has an abundance of snags that provide foraging, shelter, caching, perching and nesting sites for birds. There was a diverse array of cavities ranging in size, texture, age and location on the snag. Some of the smaller circular holes had diameters of ¼ inch, 1 inch and 2 inches. Other larger cavities varied in size and shape and various trees had loose or missing bark. Whether a cavity is located higher up on the snag or lower may indicate whether it was used for nesting or shelter since the higher cavity may provide more protection from predators. A review of ebird observations for the past year indicates that Pileated Woodpecker, Downy Woodpecker and Northern Flicker have been observed here. On several snags recent activity by the Pileated Woodpecker was observed with fresh wood chips on the ground at the base of several snags and elongated cavities. I poked with a stick inside some cavities, but didn't notice any movement. Some snags were soft or hollow inside showing signs of decomposition and others had a more solid inner core. On the more solid snags, some round small cavities were filled with leaf litter. Woodpeckers are able to excavate the hard core snags, and the cavities they create can be utilized by smaller birds like the Black-capped Chickadee, Tufted Titmouse and White-breasted Nuthatch. The Pileated Woodpecker excavates different cavities for nesting and roosting. Snags are so important for birds and other wildlife that in forest management plans, foresters recommend maintaining a certain number per acre depending on the area. One snag near the trail's edge had a painted X which may indicate that it posed a hazard and is scheduled for removal.
Date: March 6, 2021
Observation Period: 3:10 p.m. - 3:30 p.m. (20 minutes)
Location: Gilbrook Natural Area, Winooski, VT .5 miles
Weather: 23 degrees, cloudy, wind-7 mph WNW
Habitat: listed above
I returned to Gilbrook Natural Area today to see if I could spot any Pileated Woodpeckers. I didn't go far on the trail because it was too icy. The only birds I saw were two American Crows that stopped for a drink of water that had melted amidst the frozen reservoir.
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