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Bird Irruptions

Common Redpolls Appearing

1-26-15 common redpoll male 077The birds most commonly associated with winter irruptions are the winter finches — Pine Grosbeak, Red Crossbill, White-winged Crossbill, Purple Finch, Pine Siskin, Common Redpoll, and Evening Grosbeak. Their food supply, or lack thereof, in the Canadian boreal forests where they normally overwinter, determines whether or not they will be seen as far south as the U. S. Key trees affecting finch movements in the boreal forest are spruces, birches and mountain-ashes.

Common Redpolls feed primarily on the catkins (seed-containing fruit) produced by birch and alder trees. When catkin production is low further north, as it is this winter, Common Redpolls leave these areas and irrupt into areas where food is more plentiful. (Photo: male Common Redpoll)

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Snowy Owls Headed North

4-21-14 flying snowy 046The record number of Snowy Owls that spent the winter in New England are turning up in all sorts of new locations now that they are on their way back to their breeding grounds on the open tundra and stopping to refuel along the way. Although many were young birds, and won’t breed this year, the adult owls will when they reach the Arctic in a few weeks. First, the males perform aerial and ground displays. After mating, the female selects a nest site. In addition to having a sufficient food supply, the site must be snow-free, not subject to flooding, and command a view of its surroundings. The latter is achieved by making their nest on a hummock, or slightly raised surface of bare ground. The female scrapes a shallow depression in the earth with her claws, twirling around to make a form-fitted hollow. No insulating material is added to this depression – no vegetation, no feather lining. Eggs and nestlings are totally dependent upon the mother’s warmth, transmitted via the large, featherless, pink patch of skin on her belly known as an “incubation patch.” The female alone incubates the eggs and broods the young chicks while the male provides food for his entire family.

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Snowy Owl Pellet

3-25-14 snowy owl  203Your knowledgeable ID skills regarding yesterday’s Mystery Photo were most impressive!

Snowy Owls are the heaviest owls in North America, weighing roughly 4 pounds (a Great Gray Owl is only 2.4 pounds). A lot of fuel is needed to power this magnificent raptor. In the Arctic, where they live, lemmings are their preferred prey — one owl may eat more than 1,600 of these small rodents in a single year. This winter the Northeast has experienced record numbers of visiting Snowy Owls. A banner year for the Arctic lemming population followed by prolific nesting success for Snowy Owls resulted in an unprecedented “irruption” of these owls further south this winter.

While we do have lemmings in New England, they are uncommon, so Snowy Owls have relied on our small rodent, squirrel, rabbit and hare populations for food. Those owls wintering on the coast, where dunes and moors closely resemble their tundra habitat, have also taken advantage of the large number of sea ducks. As witnessed and described by Nantucket ornithologist Edie Ray, the owls fly up to great heights over the sea, spot waterfowl and then plummet down to just above the surface of the ocean where they sink their talons into a “sitting duck.” As a result, the indigestible bones, teeth and nails of prey are protectively wrapped in feathers as well as fur in the large pellets coughed up by these owls. (Snowy Owl locators: Edie Ray and Sadie Richards; Snowy Owl pellet finder: Sadie Richards)

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Northern Hawk Owl

n. hawk owl3- 231The Northern Hawk Owl is a bird of the remote Alaskan and Canadian boreal forests. Its name reflects the fact that this diurnal owl has both the appearance and behavior of a hawk, specifically, an accipiter. Although the Northern Hawk Owl winters throughout its breeding range, it periodically erupts southward into southern Canada and the northern United States. Sightings of this bird are rare in Vermont, but in recent winters, including the current one, there have been some. As with Snowy Owls, the magnitude and extent of these winter irruptions are thought to correlate with high reproductive success followed by severe winter conditions and decreased prey availability, but much remains to be understood about their winter dispersal habits. What we do know is that the Northern Hawk Owl’s skills as a hunter are very impressive. It can detect prey (small rodents, grouse, hares) by sight at a distance of half a mile and just using its ears can find prey under a foot of snow.

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Few Northern Finches This Winter

11-27-13  pine siskin-irruption forecast IMG_8713Every year Ron Pittaway of the Ontario Field Ornithologists (http://www.jeaniron.ca/2013/forecast.htm) forecasts the extent to which birds in the Finch family are expected to inundate northern New England in the coming winter. This year’s forecast is not looking great for birders hoping to see influxes (irruptions) of northern seed-eating species such as pine siskins (pictured), crossbills, redpolls, grosbeaks and finches. The reason for the lack of inundations of feathered northern visitors this winter is that the Canadian crop of seeds that these birds eat is more than ample this year, making it unnecessary for most seed-eating birds to come further south seeking food. With the exception of white pine, there is an abundance of cone crops as well as birch, alder and mountain-ash seeds and fruits this year in the boreal forests of Ontario and southern Quebec. Although there will be some southern movement of these birds, this is not predicted to be an irruptive winter, which bodes well for seed-eating birds, but not so much for bird-seeking humans.

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Bohemian Waxwings

2-27-13 bohemian waxwings2 IMG_4496Bohemian waxwings breed in Alaska and northwest Canada, but are known for their tendency to move south in the winter when their winter diet of fruit becomes scarce. These irruptions can occur in huge numbers – thousands of birds, in some cases. Their name reflects their nomadic tendency (much like gypsies, or bohemians) and their unpredictable migration patterns. Mountain ash, juniper, cedar and holly berries are among their favorite foods, and typically they will stay in an area with an abundant food source until that food is stripped before moving on. Like their relatives, cedar waxwings, with whom they often flock, they are susceptible to alcohol intoxication, and even death, from eating fermented fruit. Someone I know who was unaware of this phenomenon was alarmed when she observed a number of waxwings lying on the ground outside her house, looking for all the world as if they were dead. To her great relief (and disbelief), an hour or two later the ground was bare, the inebriated birds having sobered up and departed.