Field Observation 6: Reproductive Ecology

DATE: April 21, 2019
TIME: 2:20 PM
LOCATION: Casavant Natural Area, Winooski, VT
WEATHER: Warm. 21°C. Light winds SSW at 12 mph. Mostly sunny (UV: 6/10).
HABITAT: Deciduous forest with a river running through it. Dense canopy. Very flooded on this date.
Spring is a productive time of year for birds. The weather is warming up again, food is becoming more abundant, and for many species, it is time to find a mate. For bird species that are returning from their spring migration, the males typically arrive before the females. The male Red-winged Blackbird needs to do a lot of preparation before the females show up. The quality of the territory that he is able to defend from other males is the main incentive for a female to choose him as her mate. I heard a male blackbird perform its signature “conk-la-ree!” song, coming from a patch of trees on the edge of a pond. He uses this song to invite females to come over and evaluate the territory he has been defending for their return. He may also have been using this song for territorial reasons. Many of the songs and calls that can be heard this time of year are based in mate attraction. For the Song Sparrow and the Black-capped Chickadee, both the males and females vocalize songs in a call and response fashion, giving each other clues about their locations. The male is also giving the female clues about his fitness through his song. If she likes what she hears, she may fly over and choose him as a mate. A similar arrangement is practiced by woodpeckers, with both the male and female utilizing their species-specific drumming pattern to attract each other.
Once a bird has found its mate, a decision must be made concerning their nest. The female American Robin will most likely decide to construct her nest in the lower half of a tree, typically hidden just below a layer of leaves. Any robins looking to nest in the Casavant Natural Area may have to wait a bit longer until the deciduous forest sprouts its leaves once again. A robin requires dead grass, twigs, and mud to make a sturdy nest. The Hairy Woodpecker will excavate and build its nest in a snag, and if this cavity becomes abandoned by the woodpecker, a chickadee might take it over for its own nest. There are lots of snags that can be found throughout the natural area, especially as one travels deeper into the forest and further away from the riverbank. The woodpecker doesn’t require many materials to build its nest once it has successfully created a cavity. The cavity is typically bare except for a bed of woodchips at the bottom. The Red-winged Blackbird will ideally build its nest in marsh vegetation or shrubs. An ideal spot in the natural area would be along the banks of the Winooski river, or on the edges of neighboring ponds. Females will typically choose to construct the nest near the ground in dense, grass-like vegetation. She will construct the nest by winding stringy plant material around upright stems, and weaving in wet vegetation. She will also add wet leaves, wood, and mud inside of the nest, and line the nest with a final layer of dry grasses. The robin, woodpecker, and blackbird have all fine-tuned their methods for nesting. Each method has its pros and cons: for example, the woodpecker nest will be difficult for aerial predators to see from above, but the eggs still face predation risks by tree-climbing predators such as the grey squirrel. Different species of birds have varying preferences and have to actively choose between ecological trade-offs when it comes to deciding where to place their nests.

Publicado el abril 22, 2019 07:49 TARDE por jessharkness2