Sunday, September 30, 2007
Because chickadees are so small, it takes a lot of food during the winter to stay warm and alive. A chickadee weighs about the same as two quarters and will easily fit on the palm of your hand. Chickadees have a high surface-area to volume ratio which means that heat loss through radiation during the cold winter can be acute. Combine this with the short daylight hours in which to forage, and food for energy can be a problem.
Chickadees prepare for the onslaught of winter by storing food. Watch them at your feeders in the fall and you will notice that they eat some of the seed, but they also carry away one seed at a time, trip after trip. They stuff the seeds in the cracks of tree bark or even in little holes and cracks on your house. I have often found a few seeds crammed into little holes when painting my house.
Chickadees store thousands of food items a year. Each cache site is usually used only one time. One study found that they could find a cache up to 28 days later. How do they find these sites when they need them most? Songbirds have a very poor sense of smell, so they are not tracking the seed down like a dog.
Experiments have shown that they use a complex hierarchy of visual and spatial clues to return to each cache site. Chickadees search for caches in places suggested by large landmarks such as the arrangement of trees or buildings, then they cue on local items such as a certain tree, then by things right around the cache site such as a patch of lichen on tree bark.
How do they remember all the cache locations and the cues to get to them with a brain that would fit on a quarter dollar? They grow brain cells. The hippocampus region of their brain expands in volume approximately 30 percent each fall from the addition of new nerve cells. This region of the brain is an important area for making new memories, especially spatial memories.
The addition of new cells and the size of the hippocampus fluctuate seasonally in chickadees, with the peak in the fall during the food cache season and is the least during the summer when food caches are not necessary. It is probably energetically costly to maintain those brain cells, so when they don’t need them in the summer, they don’t replace them.
It turns out that you aren’t a bird brain after all for losing your keys once again. You’re actually a squirrel brain. They store a lot of nuts, but apparently don’t have the trick of growing their brains each year.
This week’s noteworthy birds
Periodic cold fronts continue to spill migrants across Vermont. Birders reported over 10 species of warblers. These birds are in winter plumage now, making them a challenge for even the seasoned birders.
Ruby-throated hummingbirds continue to be reported at bird feeders around the state. Most hummingbirds will be gone by the first week of October.
A buff-breasted sandpiper was see at the Charlotte Town Beach area on the 22nd. A large flock of 40 blue-winged teal were found at Herrick’s Cove in Rockingham on Sept. 23. A red-necked phalarope was spotted at Dead Creek Wildlife Management Area on Sept. 24. A peregrine falcon was observed on the University of Vermont water tower the same day.
You can explore all the birds reported last week in Vermont and add your own sightings at Vermont eBird.
Friday, September 21, 2007
Fall is the best time of year to observe migrating hawks, which depend on certain weather conditions to “fuel” their south-bound movements. So keeping an ear tuned to the weather forecast will provide a good clue as to when the best conditions exist for seeing migrating raptors, sometimes in great numbers.
Unlike passerines, waterfowl, or shorebirds which utilize stopover habitats to build up fat reserves that power their migratory flights, raptors are top predators on a limited energy budget. So while the migrations of other groups of birds consist of long bouts of nearly continuous flapping, raptors avoid such strenuous exertion at all costs. Instead, they wait for conditions that create updrafts for lift, and winds that will blow them in the direction they wish to go.
Ideal hawk-watching conditions occur when a cold front passes through the region, bringing bright sunshine and cool, strong winds out of the northwest. As the sun warms the earth it creates thermals – bubbles of warm air that rise like hot air balloons. To migrating hawks, thermals serve as elevators, giving them a free ride to the upper “floors” of the atmosphere. When hawks locate a thermal, they soar in circles, spiraling upward, often to great heights. Frequently, many hawks will use the same thermal, swirling and criss-crossing together like a boiling pot of hawks – a phenomenon known as a kettle. When they reach the upper levels of the thermal, hawks begin peeling off one by one on set wings, riding the northwest tailwind, sometime for miles, to the next thermal.
Hawks will also use deflective currents to gain lift on days with poor thermal activity. Deflective currents are simply strong winds that are deflected upward by topographic features such as mountains or cliffs. While these currents may not bring hawks to the great heights provided by thermals, they can sometimes provide better viewing conditions since the birds are not as high.
While most any open hilltop that affords a good, unobstructed view to the north and northwest could provide good looks at migrating hawks, two spots in
With the passage of several cold fronts last week, both of these sites witnessed remarkable movements of hawks. On Monday, Sept. 10,
You can explore all the birds reported last week in
Thursday, September 13, 2007
From its scattered (and still poorly known) breeding locations between western Alaska and Hudson Bay, Hudsonian Godwits undertake a marathon southbound journey that lands them in marshes and coastal mudflats of southern South America. Their route apparently involves a series of long, non-stop flights, punctuated by a very few key staging areas at which they stop to replenish energy stores. The western James Bay coast and several lakes in south-central Saskatchewan are among the most important of these sites. Most eastern birds are believed to fly nonstop from James Bay to South America, a distance of at least 4,500 kilometers. A handful of sites along the eastern U.S. coast regularly support staging Hudsonian Godwits, but numbers rarely exceed 100 individuals.
The entire North American population of Hudsonian Godwits is believed to number only 50,000 birds, and the species’ reliance on a small number of disjunct sites for breeding and migration leaves it vulnerable to habitat loss or degradation. Although population trend data are scant, the species currently appears to be stable. The brief appearance of an individual in Vermont last week is all the more remarkable in light of this enigmatic species’ epic migration.
Migrant shorebirds dominated the past week’s birding highlights, as is typical for late summer. Most reports were from the Dead Creek area, with the Brilyea Access yielding the most reliable viewing. In addition to good numbers of the “usuals” (maxima of 12 Semipalmated Plovers, 28 Greater Yellowlegs, 85 Lesser Yellowlegs, 155 Semipalmated Sandpipers, 25 Least Sandpipers, 4 Pectoral Sandpipers, and 2 Short-billed Dowitchers), the following uncommon species were observed: 3 Stilt Sandpipers, 1 Sanderling, 2 Western Sandpipers, 1 White-rumped Sandpiper, 3 Baird’s Sandpipers, and 2 Buff-breasted Sandpipers. Shorebird diversity and abundance should be at their peak over the first half of this month, so birders wishing to test their identification skills on this challenging group should visit the Dead Creek area.
You can explore all the birds reported last week in Vermont and add your own sightings at VT eBird.
Tuesday, September 11, 2007
Juvenile merlin stretching its wings.
S. Faccio 2003
The gathering of thousands of migrating shorebirds is not only about the flights and feathers to behold. To some opportunists, it is a smorgasbord not for the eyes, but for the belly.
If you visit Dead Creek, watch for shorebird flocks that suddenly lift from the ground. On the surface their movements appear whimsical. But with a keen eye and some patience, you may see a falcon in hot pursuit.
Merlins are falcons that fly low and straight, pumping their wings to attain speeds of up to 50 mph in pursuit of small birds. They are smaller than their congener, the Peregrine Falcon, and not as widely recognized. Peregrines entered the limelight when population setbacks from DDT (which also affected Merlins and other raptors) inspired a propagation program. Both species are currently exhibiting their honed hunting skills at Dead Creek.
Vermonters will see more of the Merlin in the coming years. You may know Peregrines from Vermont license plates, proudly displayed for those who donate to the state’s Nongame Wildlife Fund. Although Merlins may not encounter such fame, this small, sleek, slate-backed falcon has recently attained breeding status in Vermont.
Merlins historically bred throughout Canada and south into the Midwest and western U.S. Since the early 1980’s they expanded their range south into the northeastern U.S. The Vermont Breeding Bird Atlas documented at least 14 nesting pairs over the last 5 years, from Windsor to Sheldon Springs. Merlins prefer to nest in large pines near open areas, including human-inhabited habitat such as golf courses.
Fall migration is in full swing, with so much to see for the novice and expert birder alike.
The rains in the past week forced migrants to the ground. Flocks consisting of 8-10 species of warblers are common, including species that are rare Vermont breeders such as Cape May, Bay-breasted, and Palm Warblers. They still migrate between rain events; Swainson’s Thrushes and warblers were heard flying overhead at night.
Shorebirds are still in their glory. A Whimbrel was reported at Charlotte Beach, and “massive amounts” of shorebirds converged at Dead Creek on Saturday, including American Golden-plover, Black-bellied Plover, Semipalmated Plover, Red-necked Phalarope, Dunlin, Ruddy Turnstone, and 8 species of sandpipers.
If raptors are your rapture, now is the time to hike to a hawk migration lookout. On Mt. Philo 10 species of hawks were seen on Monday, including over 3,000 Broad-winged Hawks. Putney Mountain will also be humming with hawks.
Other sightings include 113 Great Blue Herons at Dead Creek, Common Terns in Brattleboro, and a Little Gull on Lake Champlain. A Ring-necked Pheasant with young was spotted at Dead Creek, the first Vermont breeding confirmation for this species in years.