Most studies of the effects of climate change have focused on spring phenomena. Our warming climate allows trees and bushes to leaf out earlier in the spring, providing them with a longer growing season. And many studies have shown that the same warmth allows migrating birds to arrive on their breeding grounds earlier, as it is to their advantage to claim territories as soon as their food is abundant enough to support them.
Climate change may have dramatic consequences. For example, the spring red knot migration from South America to the Arctic depends on a superabundance of horseshoe crab eggs at their Delaware Bay staging area. The shorebird migration is controlled by daylength, which is consistent from year to year, while water temperature controls when these primitive crabs lay their eggs. Warmer seawater temperatures may cause horseshoe crabs to lay their eggs earlier in the season. A large change may allow other animals to consume most of the eggs prior to the arrival of the red knots, depriving them of this critical food that fuels the final leg of their migration to the Arctic. Without this food their breeding success may be greatly reduced, threatening their survival. That is, if indeed they are strong enough to fly to the Arctic at all.
Autumnal changes are harder to document because there are a wider variety of environmental cues that can affect the timing of events. But we have discovered that warmer temperatures have multiple effects. Leaves turn bright colors and senesce later, fruits form and ripen earlier, insects are active later in the autumn and some migrating birds linger later into the autumn.
These changes may also prove to have adverse effects. Consider the hermit thrush, which depends on fruits and berries to power its southward migration every fall. While they breed on the Island in small numbers, they are much more common in the fall and some stay through the winter. They may migrate later in the autumn because of warmer temperatures, but the fruits they depend on (black cherry, huckleberry, winterberry, etc,) may mature earlier. Will other species consume the early berries before the thrushes arrive? If so, what will the thrushes eat to power their continued migration? Will they end up eating bittersweet or multiflora rose berries, thereby helping the spread of these already problematic invasive species?
Documenting these potential autumnal changes will be more difficult as they are more variable than their spring counterparts. Temperature and daylength combine to make spring events more predictable; drought, soil moisture, high winds and early frosts are additional factors that affect natural patterns in the fall, making them more variable.
Finally, many Vineyarders have commented that birds seemed to be less common this fall. Is that due to delayed southward migration because of the unusually warm weather that we have had in December? If it is delayed migration, we will eventually see the normal numbers of our winter resident birds. Stay tuned.
Bird Sightings
On Dec. 15, Lanny McDowell watched a Cooper’s hawk interacting with a flock of starlings at the Farm Institute. The flock of starlings wheeled around in unison while the hawk was harassed by a couple of crows. The hawk later caught a mourning dove out in the middle of one of the farm fields. Sarah Mayhew found 14 Bonaparte’s gulls in Menemsha on Dec. 18, in the rain. There were only three of them there the next day. They are also regularly found out in Vineyard and Nantucket Sounds, but you can see them better as they fly up and down Menemsha Channel.
Samantha Chaves found the snowy owl on Norton Point Beach on Dec. 20, as did Rick Dwyer.
Happy and Steve Spongberg observed their first white-throated sparrow of the season as it was visiting one of their watering stations on Dec. 20.
The flock of fish crows has made it out to Katama, as Warren Woessner found them there on Dec. 20. Where else have they been recently? There still is a flock of up to 20 of them hanging out between Five Corners and the Drawbridge. I have seen them there almost every day. And on Dec. 19 there were close to 100 of them in Veteran’s Park in downtown Vineyard Haven.
It is not too late to sign up to participate in the Christmas Bird Count. Feeder-watching is an important part of the count, as field teams can not possibly check every bird feeder. Please contact compiler Luanne Johnson at biodiversityworks@gmail.com to sign up and get instructions on how to conduct your feeder count.
There are lots of birds around, so please get out looking for them, and be sure to report your bird sightings to birds@mvgazette.com.
Robert Culbert leads guided birding tours and is an ecological consultant living in Vineyard Haven.
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