In the wee hours of April 29, in the full-moon-lit night sky, a Northern Mockingbird decided at 3 a.m. to give a concert outside the window of the cabin on the Refuge where I was staying. That’s not an uncommon event, well known to (sleepy and annoyed) Texans through the ages. But do that around a Texas birder who primarily tallies species by ear, and you have an interesting dynamic: a pop quiz of bird sounds. I am regularly amused and impressed when a mockingbird faithfully reproduces the territorial calls of some of our other local birds. The titmouse, cardinal, bobwhite, blue jay, and chuck-will's-widow are always on the playlist.
But every few years, I hear a mockingbird that clearly took lessons from a set of neighbors that bear a geographic imprint from a distant land. With nothing better to do at 3 a.m., I took pen and paper, sat out on the porch, and began to tally the species I could recognize from this particular individual. In rough order of the abundance of repeated calls or song phrases, here is some of what my ear detected from this mocker in a ten-minute sample (...and these weren’t rough approximations of the sounds; these were faithful, head-turning, CD-quality utterances of diagnostic sounds of these other critters):
Black-crested Titmouse, 18 calls
Ash-throated Flycatcher (2 different phrases), 15 calls
* Great Kiskadee, 13+ calls
* Green Jay, 12 calls
* Long-billed Thrasher, 10 calls
Northern Bobwhite (covey call), 10 calls
Blue-gray Gnatcatcher, 10 calls
* Audubon’s Oriole, 6 distinctive low whistles
* Cactus Wren, 5 or more calls
Greater Yellowlegs, 5 calls
Western Kingbird/Scissortail, 5 calls (dawn calls)
House Wren, 5 calls
Ladder-backed Woodpecker, 4+ calls
Barn Swallow, 4 calls
Bewick’s Wren, 4 calls
* Curve-billed Thrasher, 4 whistles
American Kestrel, 4 calls
Blue Jay/Red-shouldered Hawk, 4 calls
* Couch’s Kingbird, 3 calls
* Northern Beardless Tyrannulet (?), 2 calls
Rock Wren (?), at least 2 calls
A large portion of the sounds of any mockingbird are generic or unattributable to one bird species, and the concert goes by so fast that I’m sure I overlooked or misclassified some sounds, especially in my groggy 3 a.m. state of mind. Notwithstanding these sources of potential error, there is just no way that this particular bird would have been exposed to this combined set of distinctive sounds outside of deep South Texas, especially the subtropical species marked by an asterisk (*). Some of these birds range uncommonly as far north as San Antonio, but assuming that there might be some gross correlation of the frequency in the mockingbird’s repertoire with the commonness of the species around the songster, we’re talking about an origin in the Lower Rio Grande Valley at the closest (e.g. from the environs of a place such as Santa Ana NWR or Laguna Atascosa NWR).
Mockingbirds are not generally regarded as a migratory species, but the young of all species relocate to begin lives of their own. Those post-fledging dispersal distances for most birds may range from a few hundred yards to a few dozen miles, but there will always be the occasional traveler who decides to pack his bags and look for greener pastures, woodland, or forest, much farther afield.
Here from Greg Lasley's Nature Photography website are some cropped images of a mockingbird surrounded by the probable South Texas neighbors from whom it apparently learned a portion of its repertoire. Hover your cursor over each image to see the species name.
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Below The Line:
Now imagine you are charged with doing a bird census in a patch of South Texas brush where you will tally all species in the dawn chorus by the songs you hear around you…and the Northern Mockingbird is the most common and noisiest species within earshot. I’ve been in this setting; it can be a complete frustration and a completely laughable task. On a route through acacia-mesquite shrublands somewhere south of Uvalde many years ago, I routinely had results at each of several stops such as: “Mockingbird, 6+; Killdeer (?), Green Jay (?), Couch's Kingbird (1 or 3?), thrasher sp. (?), …”
Another source of confusion on a South Texas breeding bird census comes from the roughly similar songs of the Northern Cardinal and its close relative, the Pyrrhuloxia, both of which can be abundant. I was forced to make up a new “species” on my tally sheet--Cardiloxia--for songs I could not distinguish.