Page 41 - Hand rearing birds second

Identification and Aging 23

Figure 2.2 House Wren hatchlings (~1 g). Note tufts of dark gray down only on dorsal tracts, thickest on
crown. They can use their wings to propel themselves, and the rear end is characteristically pointed
upwards.

Plumage
Natal down – its presence or absence and, if present, its color, pattern of distribution, and abun-
dance of neossoptiles (first feathers) – can help identify a species (see Figure 2.2). The natal down
of precocial species is abundant and covers the entire chick. Precocial chicks of Galliformes have
a particular species‐specific pattern when viewed dorsally. Woodpeckers, kingfishers, swifts, hum-
mingbirds, some vireos, some wrens, House Sparrows, and Cedar Waxwings hatch completely
naked, do not develop true down, and develop their juvenile plumage as their first feathers. Corvids
hatch naked or with barely visible down that thickens by day two or so. Some birds, such as kites
and falcons, grow two successive coats of down before they molt into their juvenile plumage.
Plumage patterns and markings on the head or tail can sometimes aid identification. Many spar-
rows have white outer tail feathers (rectrices). Some species are strongly counter‐shaded, such as
the Black Phoebe, which is dark dorsally with white underparts. Most thrush chicks are spotted.
Orange patches on the top of the rump could indicate a Cliff Swallow; rufous undertail coverts
could indicate a Gray Catbird. Most young birds resemble the adult female for purposes of protec-
tion, but a few species, such as bluebirds, will show the adult color and can be sexed at 12 days. The
posterior margin of the tail is another key in that it assumes various shapes: square in Accipiters,
rounded in ravens, pointed in pheasants and Mourning Doves, and forked in terns and Barn
Swallows.

Size and Weight
Another aid to identification is to compare the weight and size of a young bird to the weights and
sizes of species of similar measurements at the same age. Also, check to ensure the chick does not
weigh more than the adult of the species being considered. In general, a fledgling altricial chick
should weigh less than or about the same as an adult female, except in the case of species (e.g.
swallows) that weigh more than the adult when they fledge. One way to tell American Robin and
Northern Mockingbird nestlings (often mistaken for each other) apart is to note that at all stages of
life, the robin will always be larger and weigh more than the mockingbird.