Page 39 - Hand rearing birds second

Identification and Aging 21

The Key Characteristics

Altricial Versus Precocial
There are two main divisions into which baby birds are divided, altricial and precocial,
although there are numerous gradations between these extremes. Altricial chicks are blind,
more‐or‐less naked, and helpless at hatching. Parents care for altricial chicks in the nest until
they are old enough to venture into the outside world, usually at several weeks of age. Altricial
chicks include all songbirds, raptors, herons, and many others. Precocial chicks have their
eyes open, a full coat of warm downy feathers, and the ability to leave the nest as soon as they
have dried off after hatching. Parents of precocial chicks typically provide warmth at night
and protection from predators, and – although chicks are able to eat on their own – the parent
shows them what to eat, how and where to find it, and what to avoid. Precocial chicks include
most waterbirds, such as ducklings and shorebirds, plus chickens, quail, pheasants, and other
Galliformes.

Bill Shape
The beak or bill of a bird is one of its most distinguishing external features. Even without feathers,
a bird can be placed in a particular family based on its beak. Passerine hatchlings have shorter
beaks than passerine adults, but within a few days the contour of the beak begins to reveal the fam-
ily, whether a flycatcher, a finch, or a thrush. The size of a flycatcher’s beak may vary by species,
but all are wide and flattened. Most have bristles at the base and slightly hooked tips. Finches and
sparrows have short, stout, conical beaks, with a decurved culmen, and the commissure is abruptly
angulated. Thrushes and mimids have large beaks and a big gape relative to head size (see
Figure 45.3). Their beaks are variable in length (short to medium), straight, and slender, with the
culmen decurved toward the tip. Beaks of precocial chicks are miniature versions of the adult
beaks because these chicks are more developed at hatch.

Mouth Color

In passerine birds, mouth color is a reliable feature for identifying family group, with some excep-
tions. The oral cavity of the mouth is lined with soft membranes, variously colored according to
species, and consistent within most family groups. Some colors are more intense than others, some
have spots or markings on the tongue or roof of the mouth, and some have colors in the UV range.
The surrounding parts of the passerine mouth lining the edge of the bill, egg tooth, and gape
flanges (swollen corners) are predominately white, yellow, or cream‐colored (Clark 1969). If it has
been determined that the chick is a passerine, the interior mouth color will considerably narrow
the field, with choices in the yellow to orange range (Table 2.4) or pink to red range (Table 2.5). It
should be noted that although many insectivores have colors in the yellow range and many omni-
vores and granivores have colors in the red range, there are several exceptions within the trophic
categories (Ficken 1965). There are also some variations to keep in mind. Intensity of mouth color
changes as the chick develops and may even change throughout the day. Color and intensity may
be much reduced in unhealthy or cold chicks. Prominence of gape flanges varies by species, is
reported to be more conspicuous in hole‐nesting species (Kilner and Davies 1997), and regresses as
young birds become self‐feeding.