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.
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