Chestnut-sided Warbler Sitting On Eggs
Different species of birds have different numbers of broods (sets of eggs/young). Eastern Bluebirds can have up to four broods per breeding season, American Robins up to three and Eastern Phoebes often two. Chestnut-sided Warblers typically only raise one family in a summer. If weather or predation destroys their first attempt, however, they will re-nest, which is just what the pictured female Chestnut-sided Warbler is doing.
By August, a majority of birds have raised their young, but there are birds that nest late in the season, some naturally (American Goldfinches) and some, such as this Chestnut-sided Warbler, by necessity. Where birds nest, geographically, affects the number of broods they have. Birds nesting at higher latitudes tend to produce fewer broods per year. Because it gets colder earlier than further south, there is less time to raise their young. In warmer regions, birds often raise two or even three broods per year. (Thanks to Dean and Susan Greenberg for photo op.)
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Bohemian Waxwings Headed Northwest To Breeding Grounds
Northern New England and, to a lesser extent, southern New England, are visited by Bohemian Waxwings most winters. This nomadic bird often occurs in large single-species flocks, but sometimes mixes with Cedar Waxwings and/or American Robins. These flocks, varying in size from a few individuals to several hundred, and even a few thousand, range widely during migration and winter. Their dietary preference in the winter for sugary fruits makes crab apple and mountain ash trees (and the ground underneath them) as well as highbush cranberry bushes likely locations to spot them.
Most Bohemian Waxwings begin their migration to their breeding grounds in Alaska and the boreal forests of western Canada in March. Like its close relative, the Cedar Waxwing, it breeds late compared to most birds. Eggs are not laid until mid-June, presumedly in order to time the fledging of their young with the ripening fruits of summer.
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Early Arrival Dates & Climate Change
As yesterday’s post indicated, the progression in which signs of spring appear remains much the same, but the timing of this progression is changing. Ornithologists have determined that modern climate change has resulted in an advancement of spring phenology throughout the Northern Hemisphere.
Many birds are arriving on their breeding grounds earlier in response to these changing conditions. Past research has focused on correlating climatic changes on breeding grounds with early arrival. However, it appears that climate variability on the wintering grounds of temperate species also plays a part in these short-distance migrants’ arrival on their breeding grounds.
Many climatic factors are involved in this phenomenon. The annual variation in temperature on the wintering grounds of American robins was found to be strongly related to their first-arrival date. Red-winged blackbirds’ first arrival dates were most influenced by precipitation during winter and spring months.
These and other changes in migratory patterns can have life or death consequences — birds arriving early on their breeding grounds face the possibility of adverse conditions and limited resources.
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Red-osier & Silky Dogwood Fruits Ripening
Some of the most prolific flowering shrubs in the Northeast are dogwoods. In the spring, their flowers attract attention and at this time of year their colorful fruit stands out. There are many species of dogwood, two of which are Red-osier Dogwood (Cornus sericea) and Silky Dogwood (Cornus amomum). These two shrubs can be hard to tell apart, as they both have white flowers, red stems and similar foliage. In the fall, however, the color of their fruit differs, as does their pith, or central stem tissue. The mature berries of Red-osier Dogwood are dull white and its pith is also white. Silky Dogwood’s blue berries have white blotches, and its stem and branches have a salmon-colored pith.
The fruit of these dogwoods and others is an extremely important source of food for many migrating songbirds, as well as resident birds. Wood ducks, Northern Cardinals, Eastern Bluebirds, Gray Catbirds, Purple Finches, Evening Grosbeaks, American Robins, Yellow-bellied Sapsuckers, Wood and Hermit Thrushes, Red-eyed and Warbling Vireos, Cedar Waxwings and Downy Woodpeckers all consume dogwood berries.
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Crabapple Consumers
Even without much of anything to go on, all answers were correct! Although Cedar Waxwings were the predominant avian visitor to this crab apple tree when I visited it, there were also robins, starlings and crows feasting away (and presumably several other species, including turkeys, as some of you guessed, at other times).
Cedar Waxwings are among the most frugivorous (fruit-eating) birds in North America. In the winter, sugary fruits dominate their diet to such a degree that occasionally, when the fruit has become overripe and has started to ferment and produce alcohol, the waxwings can become intoxicated and, rarely, die. One individual saw that her front lawn was littered with the bodies of dead Cedar Waxwings on top of the snow, but by the time she went out to dispose of them, the drunken birds had all revived and flown away.
During the winter, Cedar Waxwings travel in flocks of up to several hundred birds. They are nomadic, roaming the countryside in search of crab apples, hawthorns and mountain ashes, as well as serviceberry, juniper, winterberry, dogwood and cedar, among others. Waxwings will descend upon a tree en masse and while perched will bend down and pluck crab apple after crab apple, swallowing them whole, one at a time. Occasionally you will see them hovering briefly in the air while plucking fruit. They are well known for “gifting” fruit to fellow waxwings.
Many birds that eat a lot of fruit separate out the seeds and then regurgitate them. Cedar Waxwings let the seeds pass through them, scarifying the seeds in their digestive tract (breaking down their outer seed coat), which, once the seeds are deposited, allows them to eventually germinate. Because of this, waxwings are considered important seed dispersers for many fruiting plants in North America (including the invasive, non-native honeysuckle which, when eaten during the time feathers are developing, causes Cedar Waxwings to develop orange, not yellow, tail bands).
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Winterberry Fruit Brightening the Landscape
Winterberry (Ilex verticilatta) fruits mature in late summer and early fall, but they are much more evident now that most of the leaves have fallen off this deciduous member of the Holly family. Because these shrubs are dioecious (male and female flowers appear on separate plants), only the female shrubs bear fruit. The bright red berries often persist through the winter and provide cedar waxwings, bluebirds and robins with food long after most fruit has disappeared.
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Avian Parents Hard At Work
To appreciate the parental demands on birds, consider the feeding habits of a pair of American Robins with a nest full of young. Both parents feed their 3 – 4 nestlings, delivering 6 – 7 feedings an hour, each one to a single nestling. (Parents tend to arrive with food at a particular location on the nest rim, so there is much jockeying for a position near this spot on the part of the nestlings.) Each nestling gets 35-40 feedings per day. This amounts to almost half a pound of food delivered to the nest every day for the 13 days that young are in the nest. Even then, the parents’ work is not done, as they continue to feed their fledglings for up to three weeks after the young leave the nest.
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