The pectoral sparrow (Arremon taciturnus) is a small species of New World sparrow first described in 1779 by Georges-Louis Leclerc. It has 2 subspecies. Like other sparrows in its family Arremon, it has pale green-to-olive wings, however its breast has a distinctive black band going across it, however in subspecies nigrirostris it is not continous and instead breaks in the center. It is found in Bolivia, Brazil, Colombia, French Guiana, Guyana, Peru, Suriname, and Venezuela. Its natural habitat is subtropical or tropical moist lowland forests. The phenology of their breeding is unknown, however they have been observed nest building as early as August and as late as December. Incubation takes 15–17 days, however the duration of the nestling and fledgling stages are unknown due to a lack of research. They are omnivorous, mainly eating insects and seeds, and are considered a least-concern species by BirdLife International due to their large population and range.
The pectoral sparrow was described in 1779 by French polymath Georges-Louis Leclerc, Comte de Buffon in his Histoire Naturelle des Oiseaux under the French name "L'Oiseau Silencieux".[2][3] It was also illustrated in a hand-colored plate that was produced to accompany Buffon's book.[4] Buffon did not use binomial names but in 1783 the French naturalist Johann Hermann coined the name Tanagra taciturna.[5] The specific epithet taciturnus is the Latin word for "silent" or "quiet".[6] The species is now placed in the genusArremon that was erected by the French ornithologist Louis Pierre Vieillot in 1816 with the pectoral sparrow as the type species.[7][8]
A. t. nigrirostris(Sclater, 1886) — Found in southeast Peru and north Bolivia. Unlike nominate, its breast band is not continuous and instead breaks in the center. Its name comes from Latinniger and rostris (derived from the word for bill, rostrum) meaning black-billed. [9]
The pectoral sparrow is sexually dimorphic, and, as the name implies, sparrow-sized, at 15cm (5.9in) in length and 24g (0.85oz) in weight.[10][11] Its upperparts are pale green, becoming yellow near the bend of the wing. The head is black, with white on its throat and as stripes on its crown. Its underparts are white or creamy, with males also having a broad black band going across their breast (a pectoral band). The beak is also black, roughly 14–15mm (0.55–0.59in) long for both males and females. Tails are 58–60 and 64–67mm (2.3–2.4 and 2.5–2.6in) and wings are 74–75 and 76–80mm (2.9–3.0 and 3.0–3.1in) for males and females respectively. Its iris is brown, and its tarsi and toes are pinkish gray.[9][10]
Male and female plumage is distinctly different, with females having dull olive upperparts instead of bright yellow, a grayish pectoral band, and greyer, darker underparts.[9]
The pectoral sparrow is fairly unique in its habitat, usually being the only small forest sparrow with a striped head in its range. They can be differentiated from the orange-billed sparrow, which they border distribution with in eastern Columbia, by the namesake orange bill, as well its inverted throat colors (black throat with a white stripe).[9]
Distribution and habitat
The pectoral sparrow is non-migratory and can be found everywhere in the Amazon Basin east of the Andes except for the western parts between the Negro and Purus rivers.[12] Besides the Amazon jungle, it is found in eastern and north-eastern Brazil.[13] They occupy altitudes up to 1,500m (4,900ft) in southern Venezuela, 1,000m (3,300ft) in southeastern Peru, and 1,300m (4,300ft) in Bolivia.[9] They do not migrate.[9] They occupy the lowland undergrowths of humid evergreen forests or secondary forests, and infrequently in lighter woodlands or coffee plantations, often when near humid wooded ravines.[9] Pair density in Peru was reported to be about 1 pair per 200 hectares (490 acres).[14]
Nests are spherical, bulky, and roofed, with an entrance on the side, around 12.1cm ×13.2cm ×12.4cm (4.8in ×5.2in ×4.9in) in length, width and height respectively, and 48g (1.7oz) in weight. They consists of 2 layers — the outer layer, which is composed of dried bamboo, leaves, roots, and twigs, totaling around 35±25g (1.23±0.88oz) in weight. The inner layer is much lighter, at 12.9±3.2g (0.46±0.11oz), and is composed of leaves(20%) and pale brown rootlets(80%).[9][15] Eggs are on average 23.6mm ×17.4mm (0.93in ×0.69in) in length and width and weighing 3.5g (0.12oz). All nests studied had 2 eggs per clutch. Egg markings are highly variable; some were completely white, others speckled with varying amounts of brown spots.[15]
Incubation is thought to take 15–17 days, with the female observed acting as the sole incubator. Incubation was done in periods, averaging 71 minutes (ranging from 8 to 323 minutes). Females averaged 7.4 trips outside the nests per day, each averaging 46 minutes, however trips increased in frequency as the eggs neared hatching, going from 61% of daylight spent incubating during days 4–10 to only 55% during days 11-15.[15]
Right after hatching, nestlings were blind and almost completely featherless, except for fine black down on their backs. Their beaks were yellow and their mouths had a bright red interior. At 3 days, nestlings were roughly 8g (0.28oz) and had small pin feathers on the wings. Nestlings would gain mass at an average of 1.8g (0.063oz) per day. Fecal sacs were solely removed by males, who also do a majority of the feeding. All nestlings studied were depredated, however, and as such the length of the hatchling period and fledgling behavior is unknown.[9]
The phenology of the pectoral sparrow is unknown, however a 2011 study by Valdez-Juarez et al. found recently laid eggs across the entire period of the study, from late August to early December.[15][9] Additionally, out of the 15 nests studied, only 2 eventually hatched, the remaining having been abandoned or predated upon.[15]
Feeding
Feeding behavior is not well studied.[9] They have been observed foraging on the ground, mainly eating insects and seeds, and to a lesser extent various fruits. Studies on stomach contents in Brazil and Suriname showed various beetles, true bugs and ants, along with other insects and a small amount of grass and seeds. Adults have been observed bringing insect limbs to the nest for feeding.[9][15]
The song of the pectoral sparrow is a high-pitched buzz, consisting of very short tzik notes (initial tzik note may be slightly faster, and lower in pitch.) and usually followed by 2-4 longer, almost identical tzzzzzz notes. The entire song lasts for 2–3 seconds, at a pitch of 8 kilohertz.[9] It may also sometimes use its tzik note as a call along with a rising seet, which ascends from 8-9 to 10-12 khz and lasts for 100ms. Calls are repeated a few times, however if the bird is excited, calls may be given very quickly or continuously.[9]
Conservation
According to BirdLife International, the pectoral sparrow is a least-concern species due to its large range of 9,910,000km2 (3,830,000sqmi) and large population size not meeting the criteria for vulnerable. The population size is declining at an estimated rate of 5–9% over the 2016–2026 period.[16]
↑Ridgely, Robert S.; Tudor, Guy; Brown, William L. (1989). The birds of South America. World Wildlife Fund (U.S.) (1sted.). Austin: University of Texas Press. ISBN978-0-292-70756-6.
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