Wednesday, September 24, 2008
The Midwinter Bald Eagle Survey takes place during the first two weeks of January each year. The U.S. Army Corps of Engineers coordinates the Midwinter Bald Eagle Survey, in which several hundred individuals count eagles along standard, non-overlapping survey routes.
The data available from this website were used in an analysis of count trends from 1986-2005. This 20-year analysis used the same methods used in a peer-reviewed 15-year trend analysis (Steenhof, K., L. Bond, K.K. Bates and L.L. Leppert. 2002. Trends in midwinter counts of Bald eagles in the contiguous United States, 1986-2000. Bird Populations 6:21-32).
This site provides access to results of Midwinter Bald Eagle Surveys conducted from 1986-2005 along 746 routes in 43 states. You can retrieve raw count data as well as summary information (trends, means, high and low counts) for survey routes.
In our part of the world, the report highlights population declines of more than 50% over the last 40 years for 20 of North America’s most common bird species.
The story is the same for birds migrating between North America and Latin America. Over half (57%) of neotropical migrants monitored on their breeding grounds have suffered from population declines over the last four decades.
Wednesday, September 17, 2008
Cape May Warbler in fall plumage, JD Phillips
I have six weather forecast pages saved on my browser. We are in the thick of bird migration, but the quality of birding depends largely on the weather. Birds move when conditions are right, and knowing when to grab the binoculars is at least as important as knowing where to go.
Weather is a fine-tuner of bird migration, determining the particular days a bird will move. The length of daylight (photoperiod) orchestrates the general timing of migration, dictating the months when a species is on the move. Get a copy of “Birdwatching in Vermont” (Pfeiffer and Murin) to find out when species are generally expected to pass through, and where to find them.
Then, get cozy with meteorology. A thorough understanding of weather patterns is ideal for translating the weather forecast into a bird migration forecast. But a few tips will go a long way toward helping you to decide whether your time is better spent stacking wood.
Most of our weather comes from the west. When a low pressure system (rotates counterclockwise) is followed by a high pressure system (rotates clockwise), winds come out of the north. This is the classic “cold front.” End of meteorology lesson, on to the birds.
In autumn, birds take advantage of northerly winds produced by the change in pressure systems and surf the tailwinds. The farther north the front extends, the more birds it will sweep along with it.
Songbirds are most easily seen in “fallout” conditions: weather that makes the birds move followed by weather that forces them to stop. If a southbound cold front stops or reverses, and especially if it brings precipitation, birds will literally drop out of the sky to forage until conditions are favorable again. On a drizzly, calm, overcast morning following the arrival of a cold front, the trees are dripping with warblers.
When the north winds are too strong for warbler-watching, Lake Champlain offers a waterbird rush hour. Visit a shoreline offering good views with a spotting scope to see hundreds to thousands of loons, ducks, gulls, geese, cormorants, and terns pumping down the lake, especially in the early morning.
When the waterbirds peter out, move on to raptors. The best time to view raptor migration is late morning through early afternoon. As the earth warms, heat rises in columns or “thermals.” Raptors use the rising air to soar upwards in a circular fashion (forming “kettles”), then “stream” directly south on the tailwind until they reach another thermal. A ceiling of clouds provides a helpful backdrop for seeing the “dots” in the sky and keeps raptors from flying too high, but rain will ground them.
Now let’s put these tips into practice. A cold front blew in on Monday, bringing north winds and a cool, clear night. Predictably, birding was good on Tuesday for songbirds and raptors, less so for waterbirds because winds were light. Then a high pressure system moved in and winds shifted to the southeast; time to stack wood. At this writing, a weak cold front arriving Wednesday night with predicted north winds and some precipitation might make for decent birding on Thursday.
Other Bird Sightings
Migration highlights from 10-17 Sept. included 1247 broad-winged hawks seen from atop Mount Philo in one day, a golden eagle in Middlebury, and several songbirds not often seen in Vermont during the breeding season: Philadelphia vireos , and Wilson’s, palm, Tennessee, orange-crowned, bay-breasted, and Cape May warblers.
Shorebird highlights include a group of 13 American golden plovers and a buff-breasted sandpiper at Dead Creek. A glossy ibis and a dunlin were seen in Shoreham, and pomarine and parasitic jaegers have been seen from Charlotte Town Beach. The first of the snow geese have appeared at Dead Creek, initiating one of Vermont’s finest annual bird migration spectacles.
You can explore all the birds reported last week in Vermont and add your own sightings at Vermont eBird.
- Rosalind Renfrew
Friday, September 12, 2008
Imagine the surprise of an avid birdwatcher who visited Red Rocks Park in South Burlington last Sunday, September 9, and observed 15 species of warblers. Among these, was a rarely observed denizen of the South. Yellow-throated Warblers breed throughout much of the southeastern
You can explore all the birds reported last week in
(Yellow-throated Warbler photo by crookrw's photostream on flickr, creative commons)
Sunday, September 07, 2008
The Savannah Sparrow is a grassland bird that nests in hayfields, sedge meadows and marshes throughout Vermont. While similar in appearance to the ubiquitous Song Sparrow, the slightly smaller Savannah Sparrow has a yellow eyebrow stripe and a softer, buzzier song.
Savannah Sparrows are unique among our common grassland birds in that most maintain their breeding territories after a hayfield is cut and renest soon thereafter, even when their first nest failed due to haying. This means that their second nesting attempt is made in a dramatically altered habitat containing less insect prey. Recently, researchers at the University of Vermont used harvested and unharvested hayfields as a large-scale food-manipulation experiment to test whether a loss of prey affected the ability of Savannah Sparrows to raise young.
Reporting in the current issue of the ornithological journal, The Auk, Nathan Zalik and Allan Strong – both of UVM's Rubenstein School of Environment and Natural Resources – studied Savannah Sparrows over two breeding seasons on cut and uncut fields in Shelburne and Hinesburg. They collected insect samples every two weeks and monitored nest success throughout the summer.
The biologists found that insect and other invertebrate prey declined by 28 to 56 percent on harvested fields, while the invertebrate population continued to increase over the summer on unharvested fields. By video taping nests, they were able to determine that birds nesting in unharvested fields delivered 73 percent more food to their young than those nesting in hayed fields. Surprisingly, this did not result in differences in either the average weight of nestlings or the weight of the smallest chick in each nest. And while they found no difference in the average number of eggs per nest between cut and uncut fields, the number of young fledged per successful nest was lower on cut fields only if the nest was completed late in the season (after June 24). The number of young fledged from early-season nests was the same on hayed and unhayed fields.
According to Zalik and Strong, their results "suggest that adult Savannah Sparrows must compensate for reduced food availability on harvested hayfields, possibly by increasing the total time spent foraging."
Recent Bird Sightings
Highlights this week include a juvenile Black-legged Kittiwake sighted at Shelburne Bay, sightings of Black-headed Gulls at Charlotte Town Beach and Grand Isle, and four Phalaropes (species undetermined) at the Charlotte Town Beach. In addition, Common Nighthawks have been observed migrating through the region, including 17 reported in West Brattleboro, 46 in Norwich, three in Essex, two at Dead Creek and one in Morrisville. You can explore all the birds reported last week in Vermont and add your own sightings at Vermont eBird.