What is a passerine?

In the context of Sonoma County, passerines include locally occurring members of the following groups:

Tyrant flycatchers

Shrikes

Vireos

Corvids (crows, ravens, jays, and magpies)

Larks (Horned Lark being our only normally occurring representative)

Swallows and martins

Chickadees and titmice

Bushtits (Bushtit being our only normally occurring representative)

Nuthatches and creepers

Wrens and dippers

Kinglets

Sylvid warblers (Wrentit being our only normally occurring representative)

Gnatcatchers (Blue-gray Gnatcatcher being our only normally occurring representative)

Thrushes

Mockingbirds and thrashers

Starlings (the introduced European Starling being our only normally occurring representative)

Wagtails and pipits (American Pipit being our only normally occurring representative)

Waxwings (Cedar Waxwing being our only normally occurring representative)

Silky flycatchers (Phainopepla--a rare bird in Sonoma County--our only representative)

Wood warblers

Emberizidae (towhees, sparrows, and juncos)

Cardinalidae (Piranga tanagers, grosbeaks, and buntings)

Icteridae (meadowlarks, blackbirds, cowbirds, grackles, and orioles)

Fringillidae (Evening Grosbeak and our locally occurring finches)

What is a passerine?

There are a number of ways to answer that question--not all of them immediately helpful. The simplest answer is to say that a passerine is any bird of the order Passeriformes (but that immediately raises a new question--what characterizes birds placed in that order?) Other answers might include: Passerines are songbirds, or passerines are perching birds. A cumbersome but more practical answer for the bird watcher might involve listing all birds that are passerines, but, most birds on the planet are passerines (around 6,000 species--roughly 60% of living world bird species--according to Colin Tudge in The Bird: A Natural History of Who Birds Are, Where They Came From, and How They Live). To make such a list for Sonoma County would be an easier task (in fact, the Passerines page on this website does precisely that). Simply listing birds, however, leaves the curious mind the task of guessing what unites these apparently divergent species, and it is not an especially efficient way to answer the question we started with: What is a passerine?

Passerines have a foot structure that sets them apart from other birds. While that is not the only feature that makes a passerine a passerine*, it is perhaps the most important. The passerine foot has three forward-pointing toes and one backward-pointing toe. The toes are joined at the same level of the foot. The rear toe often curves forward, which makes the passerine foot ideal for grasping twigs and branches. This arrangement is called anisodactyly. The passerine foot is designed to automatically grip and lock through a unique combination of muscles and tendons that cause the foot to automatically latch on to a perch. It is this feature that allows true perching birds--the passerines--to roost in trees and sleep without falling to the ground. Convenient, indeed. The photo here shows the feet of a Fox Sparrow (Passerella iliaca).

Passerine feet are very different from the feet of waterbirds, raptors, and birds of other groups adapted to different habitats and lifestyles. It should be obvious that such birds can "perch" in the vernacular sense of balancing atop something, but a duck's foot, for example, is adapted for paddling, not grasping, and ducks are incapable of perching by grasping a limb. The Western Gull (Larus occidentalis) pictured at left is another example of a bird with feet adapted for paddling rather than perching. Birds such as woodpeckers and parrots can grab a perch, but these are mostly zygodactylic--having two forward-pointing toes and two backward-pointing toes (useful for clinging to tree trunks)--and they lack the muscle structure that makes the passerine foot so good at its job.

The name "passerine" comes from the Latin passer, which means "sparrow." The bird pictured at the top of this page is Passer domesticus, the common House Sparrow, introduced from Europe. Passerines are sometimes equated with songbirds because the Passeri, the largest suborder of the Passeriformae, are notably good songsters, having better-developed muscles to control the syrinx (the bird equivalent of our larynx) than any other group of birds. The Passeri are also referred to as oscines (from Latin oscen, meaning "songbird").

The birds that seem most like they ought to be passerines that aren't passerines may be our locally occurring hummingbirds, woodpeckers, kingfishers, and, especially, pigeons and doves.

*According to Tudge (quoting 1982 research by Robert J. Raikow), passerines share as many as 18 distinctive characteristics, of which five are unique to the group: See The Bird: A Natural History of Who Birds Are, Where They Came From, and How They Live (Crown, 2008), p. 171ff.

RETURN TO FRONT PAGE

Unless noted, all photos by the author. If you would like to use one of my images, please ask for permission for non-commercial use with proper credit or commercial use with proper compensation.

ctalcroft@yahoo.com

California Towhee (Melozone crissalis), a common Sonoma County passerine.

Note the three forward-pointing toes

The passerine foot from behind: One toe. Bewick's Wren (Thyromanes bewickii)

The passerine foot from behind: One toe. White-throated Sparrow (Zonotrichia albicollis)

PASSERINES, NON-PASSERINES, PELAGIC SPECIES, and INTRODUCED SPECIES