zoey_november's Journal

Date: 4/3/19
Time: 8:00–9:00AM
Location: Centennial Woods, Burlington, VT
Weather: Chilly, around 32 degrees, warming up to 37 in sunny spots
Habitat: Dense mature forest of Eastern Hemlock, edge habitat composed of deciduous trees and shrubs, and open meadow with phragmites, a creek, and Staghorn Sumac.

I observed an American Robin singing an unusual version of his song high up in a tree. It sounded like a Robin's voice and had all the right notes, but they were put together in a strange order. I visually identified it as a Robin through binoculars. I wonder if this was a juvenile undergoing the song crystallization phase, trying out his voice and practicing adult song without quite getting it right yet, or just a rare form of the song that I hadn't heard before (see recording below). American Robins overwinter in Vermont, but have only starting singing territorial songs within the past several weeks. Being generalists, it is more cost-effective for them to find food here year-round than to invest a lot of energy resources in migrating to an area where the food might not even be much more available than where they were to start out with. In the summer, they can eat insects and grubs, fruit, and seeds. In the winter they can find frozen bugs in trees, fruit like crab apples and pin cherries that cling to the branches all season, and maybe even some nuts here and there. Thriving in suburbia, they might take advantage of bird feeders or anthropogenic food. Their large bodies are well-adapted to surviving the cold, with their plump shape minimizing surface area and maximizing retention of thermal mass. Dark-eyed Juncos also stick around all winter, and have similar body shapes and diets to Robins. Juncos huddle in cavities overnight for warmth in the winter, but I wonder where Robins roost when it's very cold.

In a treetop near the Robin, I heard chatter and saw smooth sleek brown birds. They were identified by Michael MacDonald (ornithology professor at UVM) as Bohemian Waxwings, facultative migrants who are passing through Vermont on the way to their breeding territories. According to the Cornell Lab of Ornithology, Bohemian Waxwings overwinter in the middle of the US, and travel up to Northern Canada and Alaska for breeding. They appear at our latitude for just a brief period in early spring, stopping over long enough to refuel. Their photosensitivity at this time of year produces hormones triggered by increasing daylight, which allows them to match their physiology with the environment so they don't fly north too early. They were taking advantage of the abnormal abundance of crab apples in the area, which had a great reproductive year and overwhelmed the consumption needs of local species.

Using the range maps and migration information provided by All About Birds (Cornell Lab of Ornithology) I determined that the average migratory distance travelled by the birds I observed totaled up to more than 12,530 miles! To put that into perspective, that's about twice the distance from Oregon, US to Santiago, Chile! Even the distance traveled by individual birds is very impressive – some Mourning Doves and Chipping Sparrows likely traveled over 2,500 miles from Southern Mexico up to Vermont and other Northeastern states.

Date: 4/23/19
Time: 7:30-9:00AM
Location: Salmon Hole, Burlington, VT
Weather: Chilly after a few days in the mid 60s, but warming up to around 45 degrees. Sunny and clear.
Habitat: Riparian flood zone, mostly open deciduous woods alongside the Winooski River. Some dense thickets of shrubby underbrush.

As the sun warmed up the air, I noticed more and more birds vocalizing, staking out breeding territory with their spring songs. I observed two large conflict events related to breeding season and territory.

First I heard and located one Downy Woodpecker, and about 5 minutes later I heard another calling from further away. The far one came progressively nearer and began chasing the first. This lasted for a couple minutes, with the two birds flying after each other and squeaking loudly. Within a short time several other Downy Woodpeckers showed up until there were around 5 or 6 chasing each other from tree to tree. There was a lot of rapid chatter, and it was hard to tell if they were mostly chasing a single individual or if they were all chasing each other. It didn’t seem to be territory-specific, because they traveled from tree to tree over a good distance without returning to a certain area. I wondered if there were any females involved, but it was difficult to tell. It may just have been a dispute to determine hierarchical ranking between males - if so, maybe it makes sense that they weren’t defending a specific spot because by deciding who the top males are, they can then allocate territory by default.

The second major commotion I noticed came from three pairs of Canada Geese staking out nest sites on an island in the river. The island was shaped so that the highest ground was upstream, and the ground sloped downward from there until it sank back under water at the downstream end. Upstream there were a few trees and bushes, and downstream there were only cattail reeds. There was one pair of geese at an upstream nest site, one in the mid-range, and one down at the soggy end of the island. Approximately every 7-10 minutes, the downstream pair would slowly begin to swim upstream until they were close to the middle pair's site. At this point, both the middle pair and the upstream pair would start displaying, honking, and hissing, working up into a frenzy and eventually charging the downstream pair. The downstream pair retreated and each pair left the water and returned to their site.

This process repeated itself for over an hour with periodic attempts from the downstream pair to upgrade their location, each time being chased off by the upstream geese. Interestingly, the dominant pair furthest upstream also attacked the middle pair during these conflicts, although the middle pair never infringed on the upstream pair's territory. After more than half a dozen such altercations, the downstream pair gave up and flew away, probably to find a better nesting site with less aggressive neighbors. I wonder what gave the dominant geese the upper hand in this situation – were they simply the first to arrive that year, or had they claimed that spot in previous breeding seasons? Were they healthier and stronger than the other geese? Younger, or older? I was left thinking about how geese decide how much energy to invest in fighting for a spot before they try to go look somewhere else.

Comparing nesting habitats, it's clear that the geese preferred higher ground and drier nest sites with good shrubby coverage close to the water's edge. Downy Woodpeckers obviously require very different nesting conditions: they are cavity nesters, and tend to prefer sloping trunks with the entrance on the underside, presumably to protect against precipitation (according to the Cornell Lab of Ornithology). Proximity to an abundant food source is also important, just as it is for the geese - so I guess this area provides good foraging for both aquatic omnivores and insectivores. I also looked into nesting habits of the Ruby-crowned Kinglet: a bird I was lucky enough to get very close to (after my camera ran out of battery!). I learned that these tiny birds can have up to 12 eggs per nest! Similar clutch size to geese, but with very different diets and energy-expenditure ratios. Like woodpeckers, their diet includes insects and small fruits and seeds, but I believe the kinglet preys on much smaller beetles whereas woodpeckers will take larvae from their tree cavities. Kinglet nests are very thick, but made from flexible spiderwebs, fur, and plant fibers to allow the nest to expand as the young grow bigger, ranging from 2 inches to 4-6 inches deep (Cornell Lab of Ornithology).

I also tried to sit and make a sound map of all the birds I could hear during the peak of the cacophony. It was difficult, as the geese drowned out a lot of the smaller birds, but I learned that Red-winged Blackbirds tended to be close to the water's edge, as did Song Sparrows. Hermit Thrushes were further uphill, and the Ruby-crowned Kinglet occupied the area in between. I also heard a couple crows and cardinals that seemed to be coming from the opposite bank of the river. Comparing my experience in the field to the recordings I brought home, I was impressed with the brain's ability to focus in on one sound in the midst of a lot of similar noise. On recording, a lot of individuality is lost and it's much harder to pick out distinct species or individuals, as all the noise is more equalized.