Brown Thrasher

The Brown Thrasher is a hiker’s bird, searching for food in the wooded thickets we share

Common Name: Brown Thrasher –  There is some conjecture as to the origin of the word thrasher, which could derive from a noun or a verb. The similarity between thrash and thrush, another common bird which is sometimes becomes thrusher in English country dialect, implies a nominal origin. They are erroneously called brown thrushes on occasion. The predicate interpretation calls attention to the long tail that flails about as if thrashing. The reddish-brown upperparts and brown-black stripes across the front both evoke a consummate brownness.

Scientific Name: Toxostoma rufum – The genus is Latin for arched or bowed (toxon) combined with mouth (stoma). This  refers to the long, curved beak that is a common thrasher characteristic. Rufum is Latin for red from which rufous or reddish-brown is derived.    

Potpourri: The Brown Thrasher has a hiker’s perspective, eschewing the cityscapes of pigeons and sparrows and the bird feeders suspended over the manicured lawns of suburbia. They are found mostly strutting through  brushy, unkempt woodland thickets, pausing only to probe for insects with a long piercing bill.  Dressed for the part, the muted brown hues of protective top feathers match the surrounding tree bark. The vertical streaks that extend over the breast from head to toe are like the reedy grasses through which they pass almost invisible.  The cryptic colors are hardly arbitrary, as they share the same wooded areas with scarlet tanagers and  goldfinches with vibrant reds and yellows that are unmistakable even at a distance. Each species follows its own blueprint, hammered out by the evolutionary pressures of survival. All are  songbirds, and the brown thrasher is the most gifted of the lot. 

Thrashers, catbirds, and mockingbirds comprise the family Mimidae, the name originating from the Greek word mimos meaning  to imitate or represent, a word applied equally to mimes as mimics.  Most but not all of the birds in the family are noted for the complexity, variability, and length of their songs, which are not infrequently taken from other birds.  They are even called mimids as a group collective name. The catbird is the least loquacious, preferring a harsh, “downslurred mew,” one of the tortured onomatopoeias favored by birders to use human vocal phonetics to describe what emanates from bird beaks.  This of course sounds like a cat’s meow and what better name for a  bird with uniform dark gray plumage which, admittedly, is not unusual as a cat color. The Northern Mockingbird is incongruously more common in the south-eastern United States. It bears the sobriquet of copying and repeating as if taunting or mocking the sounds made by other birds, the ultimate mimic. [1] The adage that it is a sin to kill a mockingbird has no ethnic roots, but was rather chosen by novelist Harper Lee as a literary metaphor for innocence destroyed by evil.

Mockingbirds are mimics, but they are bested by Brown Thrashers when it comes to repertoire

The Brown Thrasher is adumbrated by its mockingbird cousin. This is due to a combination of familiarity, mistaken identity, and cultural lore. Mockingbirds congregate with relatively high densities near human habitation and are, as mimids, accomplished virtuosos in their own right.  Many songs of the hidden and unappreciated brown thrasher are therefore mistakenly attributed to the better known mockingbirds.  Attention to auditory detail provides a clue to the true troubadour. Mockingbirds normally repeat their purloined song phrases three times in rapid succession. This distinguishes them from both the terse catbird, with its singular tone and the brown thrasher, which repeats each sound just twice. [2] These double tone repetitions follow one set after another in lengthy and involved serenades  that are not only melodically captivating but independently conceived without mimicry. Henry David Thoreau found them boon companions during his philosophical sabbatical at Walden Pond, recording their song as “drop it, cover it up, cover it up – pull it up, pull it up, pull it up.” This was refined to doublets by Cornell’s University Laboratory of Ornithology as “plant a seed, plant a seed, bury it, bury it, cover it up, cover it up, let it grow, let it grow, pull it up, pull it up, eat it, eat it.” [3] None of which makes any sense, but why should it?

Measuring bird song tonality is complex, requiring not only frequency band measurements but also statistical calculations. While this may raise doubts about absolute numbers for recorded sounds that comprise a song, comparisons between species using the same methodology are surely valid. Mockingbirds have been recorded and analyzed with a repertoire ranging from 66 to 244 song types, the variation a matter of the individuality of each bird in its selection of songs to replicate and its predilection for singing in general. The songs of the brown thrasher number in the thousands and there is some evidence that improvisation occurs spontaneously in the course of a single burst. One brown thrasher was recorded singing in staccato bursts  for 113 minutes while stationary  at a single perch using  a mixed repertoire of 4,654 separate doublet units. Further evaluation with a spectrum analyzer revealed 45 song segments of which 20 were never repeated and two were repeated seven times. The entire sonata was statistically analyzed and found to consist of 1,805 separate sounds. It is a widely held among ornithologists that brown thrashers are the most accomplished vocalists among the thousands of species of song birds. But there remains a fundamental question: what is all of the singing about? It has been observed that male brown thrashers are mostly vocal in early spring as a part of territorial reckoning. However, once they are selected by a female and begin nesting, the singing stops abruptly like an avian version of musical chairs (nests in this case). While this would suggest that the intricate songfest achieves its intent ― i. e. intimidating rivals and attracting mates, why the complexity? Most birds suffice with a note or two even when there is more competition and closer quarters. There must be another reason. [4]

Why birds sing at all is a matter of conjecture. There are some sounds with obvious purpose and there are some that can only be for an amusement akin to human whistling. Non-songbirds produce mostly instinctual noises that are known  as calls, like the quack of a duck or the honk of a goose. Songbirds also use calls for functional purposes like location and warning but the song is mostly a whimsical trill. From the physiological perspective, songbirds are unique in having a “voice box” called a syrinx which has two sides that can be independently controlled to produce two different tones at the same time. There are many unexplained sonorous behaviors, including why males are the primary singers in temperate climates (as females are in the tropics) and why there is a dawn chorus. Songbirds learn songs from their parents as nestlings in what is called the critical period and practice them after fledging, shortening the years-long human process to weeks. Absent the intricate syntax necessary for human speech, there can be no practical reason for a string of arbitrary sounds extending to the thousands employed by songbirds like  brown thrashers. [5] The dawn’s early light sing-along may provide a clue ― that it has no practical function whatsoever, but is rather an expression of the exuberance in the ineffable beauty of musical tones ― the sine qua non of feeling alive even for creatures that soar over treetops and dart acrobatically from limb to limb. [6]

Brown thrashers pair bond to procreate, incubate, and subsequently feed the nestlings that result. Unlike many birds, however, they are not monogamous, sometimes changing mates even in the middle of a single summer, but only after the teenagers have left the nest for good. The survival of avian species as the only extant relative of the dinosaurs through the Cretaceous – Paleogene extinction 65 million years ago is testimony to the evolutionary resilience of strict behavioral protocols where caring for progeny is concerned.  Once the eggs are laid by the female, they must be kept warm until they hatch two weeks later as helpless altricial chicks that must be fed until fledged. The duties of this months-long endurance test would be impossible without the dedicated support of a mate. In the case of brown thrashers, this does not mean just finding food and guarding against predators, but sharing in chick care as well.  While the numbers vary to some extent, one field observation documented that during one 14 hour period the female sat on the nest for a little under 9 hours and the male just shy of 4 hours, about thirty percent of the time. Once the eggs hatch after about two weeks of brooding time share, the feeding frenzy begins. During one particularly long day, food deliveries began at 3:30 AM and did not end until 9:00 PM during which time the female made 186 sorties and the male 98 for a total of 286, equating to a rate of about one meal every 4 minutes. Since what goes in must come out, the nest would become fouled to overflowing at this rate if the droppings of the sequestered chicks were not removed. Fouling of the nest is a serious taboo among almost all animals. Both male and female adults inspect the nest scrupulously on a regular basis and particularly after feeding to collect the accumulated excrement which they encase in a transparent bag for removal. [7] It is probably not coincidental that birds and mammals are the only two major groups of animals that are warm blooded and that invest long hours of diligent care in overseeing the growth and instruction of their progeny. Both attributes require a lot of time and energy and yield an impressive adaptive result.

Maintaining a constant body temperature inside a thin skin covered in feathers against the onslaught of environmental extremes requires a self-regulating heat engine. Heat requires the oxidation of food, the essence of metabolism. Getting more oxygen to the cells of the body requires a plumbing system that is designed for inhalation and transport ― the four-chambered heart of birds (and mammals) evolved as a result from its three chambered reptilian predecessor. The extra chamber allows for a separate pulmonary loop on one side of the heart to operate at one eighth of normal blood pressure (15 mm HG as opposed to 110 mm HG systolic in humans) so that the hemoglobin of the red blood cells can absorb oxygen in the pressure-limited lungs.[8] To make this work, a steady input of nutrient laden food is needed. Brown thrashers, like all birds, are adept omnivores. In the warmer months,  they stalk resolutely through underbrush, thrashing aside the detritus to reveal the hidden arthropod smorgasbord below.  Since the etymology of thrasher is a matter more of lore than fact, there is no reason to reject the notion that the name arose from this thrashing of the underbrush, akin to threshing grain.  In the less constrained and sometimes exploitive science of the last century, 266 brown thrashers were eviscerated to provide incontrovertible evidence of what they ate. Animal foods comprised 62.22 percent,  consisting mostly of insects (18.14 percent beetles and 5.95 percent caterpillars), a major portion of which was used to feed the gaping maws of the brood. The balance of 37.38 percent was vegetable, mostly wild berries (19.95 percent), constituting the main food source during the  winter months (45 percent in January and February). [9] The berry-bird connection is not coincidental, but rather an evolutionary advance of flowering plants, or angiosperms, allowing them to spread their seeds by embedding them in a nutritive dollop frequently colored red with provocative purpose.  

Birds are intelligent and bird brains are advanced, contrary to the pejorative epithet. Corvids are considered the most intelligent, but mimids cannot be too far behind.  Acorns, the mast of oak trees, are a popular food for brown thrashers throughout the year, but especially in November when the nuts fall to the ground. Acorns are round with hard casings to protect the oak tree seed within from being disturbed. Squirrels pick them up in their hand-like paws and gnaw through the shell with incising teeth, but birds must make do with claws and a beak. Brown thrashers have been observed excavating a shallow hole in the ground as a tool to hold an acorn firmly in place while they hammer away with repeated piecing blows to breach the protective casing. Moving the acorn from one side to the other in the depression for a better angle of attack, the inner nutmeat was fully removed and eaten. Tool-making such as this requires cause and effect reasoning that defines intelligence. [10]  There is also evidence of the employment of props as coaxing tools in the training of fledglings to take the first flying leap. A parent bird was observed with a bit of paper folded to resemble a morsel of food held over the heads of the craning chicks and repeatedly pulling it away. Having inspired rapt attention, a swift move to a nearby branch incited lunging as  the only option. [11]   Taken together, the syntax in song, the resourcefulness in repast, and the complexity in care require a least a modicum of sagacity. The brown thrasher is a very smart bird … avian sapiens.

References:

1. Rosenberg, G. “Mockingbirds and Thrashers” National Geographic Complete Birds of North America, Jonathon Alderfer, editor, National Geographic, Washington DC, pp 495-502.

2. Robbins, C. Bruun, B., and Zim, H. Birds of North America, Western Publishing Company, Racine, Wisconsin, 1983, pp 240-241.

3. Johnson, T. “Out My Backdoor: Brown Thrashers, a Special Songster” available at https://georgiawildlife.com/out-my-backdoor-brown-thrashers-special-songster

4. Kroodsma, D. & Parker, L. (1977). “Vocal virtuosity in the Brown Thrasher”. The Auk Volume 94 Number 4, 1977, pp. 783–785.

5. https://academy.allaboutbirds.org/birdsong/       

6. Hartshorne, C. “The Monotony Threshold in Singing Birds”. The Auk. Volume 77 Number 2. 1956 pp 176–192.

7. Bent, Arthur Cleveland . Life histories of North American nuthatches, wrens, thrashers and their allies. Smithsonian Institution United States National Museum Bulletin 195. United States Government Printing Office Washington, DC, 1948. pp. 351–374. file:///C:/Users/Owner/Downloads/USNMB_1951948_unit.pdf     

8. Needham, W. The Compleat Ambler, Outskirts Press, p. 336.

9. Beal, F.  et al. “Common birds of southeastern United States in relation to agriculture.” U.S. Department of  Agriculture (USDA) Farmer’s Bulletin 755, 1916,  p. 11. available at https://www.biodiversitylibrary.org/page/56848073#page/13/mode/1up      

10. Hilton, B. Jr. (1992). “Tool-making and tool-using by a Brown Thrasher (Toxostoma rufum)” The Chat Volume 56.

11. Bent, op. cit.

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