Journal archives for April 2019

April 26, 2019

Field Observation 6: Reproductive Ecology

On my walk in Red Rocks Park in South Burlington, I saw and heard many behaviors related to mate selection and territory selection and defense. In particular, I heard the songs of male Cardinals and American Robins everywhere I went, and the presence of multiple singers in each area I heard them indicates to me that singing, an energetically costly activity, is being undertaken as a way to establish territory and perhaps defend mates. This makes sense for the time of year, since we have just begun to experience the warm spring days that serve as a signal to begin mating for these species. Both Cardinals and Robins are probably nesting in the dense brushy areas immediately adjacent to the entrance trails at Red Rocks (making it easy for me to hear them). At 7:30, I observed a Northern Flicker enter a hole in a beech tree ~ 40 feet above the ground. This tree was located on a rise about 60 feet from the water. The bird very gradually peeked its head and then its body into the hole, and once it fully entered, it did not reemerge. This behavior seems consistent with the Flicker's use of nighttime roost cavities, but the Flicker also builds its nest in cavities. It does not seem unlikely that nest cavity selection is at least partly based on knowledge gained from roost cavity use, so this behavior may have been associated with nest selection. Lastly, I saw at least four Buffleheads on the bay: a male, a first-winter male, and two females. The mature male's head-crest display is striking and conspicuous and serves a role in mate selection, and occasional flapping behaviors exhibited by all the ducks (but perhaps the mature male more often) may have been courtship or dominance displays. They may nest in the vicinity of the bay, someplace quiet where there are dead trees near the water's edge.

Northern Cardinals nest in dense foliage, generally not above head-height, where the female carefully builds a nest cup with four distinct layers. Buffleheads, on the other hand, nest in hollow trees near the edges of ponds and bays. The females do not gather nest material - they simply shed some of their breast feathers and line the nest with these. Some of the nest cavities found and reused by Buffleheads are made by Northern Flickers - the same bird I saw entering a cavity in a beech tree. Flickers build their own nest cavities in dead or diseased trees using their powerful beaks, and leave the cavities bare except for a bed of wood chips.

I heard at least 7 different species during my "sound mapping" exercise. In retrospect I think it was a quiet moment to choose - it was getting cold and dark, and the birds were not singing as much as I might have expected. Interestingly, I noticed "paths" of movement in different parts of the area around me. To the north, American Crows made quiet sounds as they flew overhead from SW to NE. In the area to the west of me, a small flock of Black-capped Chickadees made chips and quiet calls as they moved through a tall stand of white pine. I heard about three Cardinals, two Robins, three American Crows, at least three Chickadees, one of what I think was a Dark-eyed Junco, and one gentle soo-see-see-see song that may have been a sub-song phase White-throated Sparrow.

Posted on April 26, 2019 01:16 by sam_blair sam_blair | 9 observations | 0 comments | Leave a comment

April 07, 2019

Field Observation 4: Migration

I went to Shelburne Pond Natural Area on Sunday, 4/7 from 3:30 to 5:00 pm. It was a mild 50°F with little to no wind and 100% cloud cover. There was no precipitation.

I walked a ~2 mile loop around the southwestern part of Shelburne Pond. I saw two male Wood Ducks (and heard a female) in the whitecedar swamp. I heard and saw a flock of Black-Capped Chickadees in this area as well. I heard and saw at least 3 Song Sparrows in brushy edge habitat near the parking lot. I saw a Common Raven fly overhead and heard many ravens on the far side of the pond. There were Canada Geese in the fields near the access road, and also in this area I saw two American Kestrels. Initially they were sitting on telephone poles, but then both individuals flew to a dead tree in the field and subsequently flew intermittently from the tree to different spots in the field. I did not see if they were feeding. I also saw some starling and a Rock Pigeon on a nearby barn.

Black-capped Chickadees and Common Ravens are both year-round residents in VT. They are both quite smart birds. The BCCH displays both physiological and behavioral adaptations to life in winter. These include food caching and the ability to enter a state of facultative hypothermia. The raven is intensely intelligent and able to exploit many food sources as they become available. However, research still shows that a high percentage of juvenile ravens do not survive their first winter. Both birds stay here year-round because they are able to find sufficient food in the winter; generally the evolutionary decision to expend energy on migration has more to do with a lack of food than with low temperature (although availability of food depends on temperature).

The Canada Goose is a facultative migrant. It travels irregularly in response to local conditions. I'm not sure where the geese I saw were coming from, but they could have been as close as southern Vermont or northern Massachusetts. They may be staying in this area for the whole breeding season. They depend on a) open water and b) agricultural or suburban open land to breed and forage, respectively. The Shelburne Pond area currently has open water in parts of its boundaries, and the fields around the pond are thawing out and quite muddy. This likely means that there is sufficient food in the form of seeds and sedges in this area for the geese to stay, and there will be more and more food available as the grasses begin to grow and the lake thaws.

The Song Sparrow is an obligate migrant. It travels as far south as Florida and northern Mexico in the winter, and breeds in Vermont and into Canada. It has arrived in the last week or two, as far as I can tell. This "choice" must be linked to food availability. The beginning of the spring thaw must bring back to "life" sufficient insects and invertebrates for subsistence in the sparrow's preferred habitat, which is brushy edge habitat near open fields or forest edges. It's important to the Song Sparrow to arrive as soon as possible after food becomes available because the spring is when Song Sparrows establish territories and begin to attract mates. An earlier bird will tend to be a more successful bird, as long as it arrives after food has become available. However, if it arrives before food is available, it will either be a very hungry or a dead bird - a definite disadvantage.

The maximum straight line distance likely traveled by the migrant species I observed is ~ 2600 (American Kestrel) + 2300 (Wood Duck) + 1600 (Song Sparrow) + 200 (Canada Goose) miles = 6,700 miles. Wow.

Posted on April 07, 2019 22:30 by sam_blair sam_blair | 8 observations | 0 comments | Leave a comment