Order
Passeriformes
Family
Mimidae
Genus
Margarops
 
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Version 1.0

This is a historic version of this account.  Current version

SPECIES

Pearly-eyed Thrasher Margarops fuscatus

Wayne J. Arendt
Version: 1.0 — Published November 17, 2017

Appearance

Distinguishing Characteristics

Pearly-eyed Thrasher is a 90–150-g, polymorphic passerine with an average body length of about 26 cm (n = 60; range 20.5-29.9 cm, SD 1.47 mm). Its upperparts and flight feathers are brown overall but there is a clinal gradation in the color of its plumage from a medium coffee brown in the extreme north, e.g., the Bahamas and Greater Antilles (M. f. fuscatus) to a darker brown hue in the northern and central Lesser Antilles (M. f. densirostris). The plumage of the St. Lucian subspecies (M. f. klinikowskii) is a rich chocolate brown with a rufous tint and slightly different markings, whereas that of M. f. bonariensis from Bonaire is generally more grayish brown.

In adults, flight feathers and primary coverts are darker, but are variable among subspecies. Feathers in several tracts are edged with tan, beige, or rufous (juveniles), depending on tract, age and subspecies. Visible portions of the breast and undertail coverts are brown (bases are gray) with white centers forming a "spearhead" pattern (oftenwith two concentric "spearheads" on the undertail coverts).

Abdomen feathers are white or buffy white, depending on age and subspecies. In some individuals, the belly appears whiter and is slightly more extensive in adult males, but this character must be used in combination with several others in attempting to sex adult thrashers.

Undertail spots are white. Spot size varies among subspecies, age groups: HY/SY: mean 12.4 mm (range 8.3-20 mm, SE = 0.78); AHY/ASY: mean 16.2 mm (range 9.7-20 mm, SE = 0.48; P = 0.014) and between sexes: FEMALES: mean 13.1 mm (range 8.3-20 mm, SE = 0.69); MALES: mean 15.9 mm (range 10-20 mm, SE = 0.64; P = 0.021) [Note: The tail spot “size” reported above pertains to the outer rectrix (no. 6) and constitutes the width at the widest white area running parallel to the barbs (not the rachis), that is, the white area measured is diagonal to, not parallel with, the rachis. The white “spot” is generally larger on the anterior (outer) vain of each bilateral feather (on each side of the uropygial gland) and the white area decreases on each feather progressing towards the center rectrices].

Other Names – Throughout the Caribbean the pearly-eye is known by more than 40 different vernacular namess in English, Spanish, Dutch, and French, including Creole and Patois. The most commonly used local names are, respectively, (1) "thrush" (used as a general descriptor); (2) "zorzal", a Spanish general translation of "thrush", e.g., Zorzal Pardo or "brown thrush" in Puerto Rico; (3) "moqueur", the French general translation of "thrush", e.g., le Moqueur Corossol or "soursop bird" in Guadeloupe; (4) Witoogspotlijster, the Dutch translation of "White-eyed Mockingbird", and Palabrua, Papiamento translation of "Black Magic Bird"; (5) grieve (pronounced "grief"), the general term used for "thrush", e.g., Grosse Grieve or "large thrush" in the Patois and Creole dialects spoken in the French West Indies and Dominica, St. Lucia, and St. Vincent (for more information see Arendt 2006a: p. 58, Table 3.2; for more vernacular synonyms, see Avibase: the world bird database).

Similar Species

Scaly-breasted Thrasher (Allenia fusca [formerly, Margarops fuscus, or M. fusca]) – Like the pearly-eye, the affinities of this similarly plumaged and former congener of the pearly-eye were obscure during the genesis of its discovery and classification. It, too, was considered a thrush by early taxonomists and was placed in several genera over a span of 54 yr (1807–1861, e.g., Muscicapa, Turdus, Margarops, and even Cichlherminia. Cory was the first to place it in the genus Allenia in 1891, but in 1902 Wells reassigned it to the genus Margarops. Shortly thereafter, however, Riley (1905) postulated that it did indeed merit its own genus and thus it was reinstated to Allenia. Still later, following early authors, Bond (1959), among others, proposed that it be reconsidered congeneric with Margarops fuscatus (also M. fuscata), and assigned a fifth species name, viz., M. fuscus ("fuscus" connotes dark or brown in Latin). More recently, however, Hunt et al. (2001) proposed two species of Scaly-breasted Thrasher and argued persuasively that it merits separation from the genus Margarops and advocated replacement in its previous genus Allenia. For more information on its taxonomic history see Arendt 2006a: page 59, Table 3.3).

The Scaly-breasted Thrasher is also known by several vernaculars (Arendt 2006a: page 60, Table 3.4). For more vernacular synonyms, see also Avibase: the world bird database).

Scaly-breasted Thrasher is smaller than Pearly-eyed Thrasher, with a shorter black (not yellow) bill, a yellow or yellow brown (not white) iris, and narrow wingbars.

The genus Mimus – There are several species within the mockingbird genus Mimus showing superficially similar plumage coloration and white or tan feather edgings in at least a few of the same anatomical areas as the pearly-eye.

Although specific areas vary among species, most in common among all species include the dorsum (mantle), wings, and tail, and especially the flight feathers (remiges, rectrices, and their respective coverts).

The following plumage characteristics vary substantially among the Mimus species (and subspecies), location (geographic, altitude, even habitat), age, and gender. However in general, as in the pearly-eye, the typical feather coloration and pattern among these species is as follows: brown lesser, medium, and greater coverts (black in some subspecies) with (and sometimes without, especially in juveniles, immatures and females) white tips and feather edgings (often russet in young birds). In some species only the median and greater coverts show this pattern. Flight feathers show a similar coloration and edging pattern (brown with white tips) but also more extensive white edging (beige or russet in immatures), often along the entire vein of the remiges (from the Latin for "oarsman", because the primary feathers propel the bird forward) and rectrices (from the Latin for "helmsman", because the tail helps the bird to brake and steer in flight). In many species, as in the pearly-eye and scaly-breast, the tertials (at least t8 and t9, and sometimes pronounced in the alula) are edged in white in the adults (russet or none in immatures and females). The rectrices are either tipped with white or show a variable amount of white (often limited to the outers). Even in species with extensive white or at least white tips on most of the rectrices, the center rectrices are often uniform brown (no white tips or edgings).

Mimus species most similar to the pearly-eye in these plumage characteristics include Long-tailed Mockingbird (Mimus longicaudatus) found in Ecuador and Peru, and species inhabiting the Galápagos Islands, e.g., Galapagos Mockingbird (Mimus parvulus), Floreana (or Charles) Mockingbird (Mimus trifasciatus), Española (or Hood) Mockingbird (Mimus macdonaldi), and San Cristobal Mockingbird (Mimus melanotis).

Although more variable, another nine Mimus species share similar plumage coloration and feather edgings (e.g., brown or black lesser, medium, and greater coverts, white tips and feather edgings): Chilean Mockingbird (Mimus thenca), Patagonian Mockingbird (Mimus patagonicus), Chalk-browed Mockingbird (Mimus saturninus), White-banded Mockingbird (Mimus triurus), Brown-backed Mockingbird (Mimus dorsalis), Bahama Mockingbird (Mimus gundlachii), Socorro Mockingbird (Mimus graysoni), Tropical Mockingbird (Mimus gilvus), and Northern Mockingbird (Mimus polyglottos).

Almost all species of Mimus, however, are allopatric to Pearly-eyed Thrasher, although the pearly-eye overlaps in the Bahamas with Bahama Mockingbird. The mockingbird easily is distinguished by its paler upperparts, black (not yellow) bill, and dull yellow or orange (not white) iris, among many other differences.

Detailed Description

Plumage characteristics – In general, down feathers of the pearly-eye are gray and body feathers of the formative and basic plumages are gray at their base (ca 1/3 of vein length of throat and crown feathers, and ½ to ¾ in upper breast, scapulars and those of the dorsum) and brown distally; shades of gray vary among islands and subspecies (see Geographic Variation), and even among individuals on the same island. Contour feathers are described below:

Upperparts: Dorsally, the feathers, including dorsal body feathers (crown, scapulars, dorsum), are dark brown with lighter grayish brown edgings, wider at the apex, especially scapulars. Shades vary with age and subspecies; brown dominates most of each visible feather (bases are varying shades of gray) with lighter, brown, tan, grayish, or beige edgings, emphasizing the shingled appearance of the overlapping feathers.

Flight feathers: The primaries, secondaries and rectrices (including their respective coverts) of pearly-eyes in basic plumage are dark brown (a rich chocolate brown). However, some of the secondary coverts can have a slightly lighter hue.

1st cycle (HY/SY) juvenile and formative plumage: Primaries (pp 5–8) are emarginated, most prominent on pp 6–8. Primaries 6–9 are notched, most prominent in pp 7–8. Emargination and notching are less extensive than in 2nd cycle and older individuals in basic plumage.

In 1st cycle individuals, the posterior (inner) webbing of the primaries and secondaries has a wide (ca 2–4 mm) beige edging, especially the inner primaries and the secondaries. The primary coverts are a somewhat lighter brown (not a rich chocolate brown) and do not contrast against the primaries as in older individuals in basic plumage. Although less discernible than in Scaly-breasted Thrasher (Allenia fusca), the remiges (and their coverts, especially primary coverts) and rectrices of HY/SY individuals are thinner and more pointed. Often, the greater (secondary) coverts show a more russet (vs. beige) tint.

In 2nd cycle and older individuals in basic plumage, primaries 5–8 are also emarginated, most prominent on pp 6–8. Primaries 6–9 are notched, most prominent in pp 7–8. Primaries, primary coverts, carpal covert, alula, and covert, are dark brownish gray. Edging on the posterior (inner) webbing of primaries is narrower (ca 1 mm wide) than in 1st cycle individuals and edging is tan to beige or even bone white.

In 2nd cycle and older individuals the secondaries can be slightly lighter brown than the primaries and the anterior (outer) webbing is thinly edged with beige or bone white. The edging on the posterior (inner) webbing is a somewhat lighter beige to tan and wider (~2–3 mm). The median secondary coverts have faint beige edgings. The greater secondary coverts are beige or tan with white edging. The tertials are tipped with white (ca 1–4 mm) that often extends proximally along the outer edge of the vane (more so than in 1st cycle individuals), depending on age, subspecies and to a lesser extent, gender.

Throat and upper breast feathers: Proximal to the rachis, 1/3 of the barb is brown. The distal 2/3 is white, giving the throat a streaked appearance; the brown base of the barbs in the lower throat and upper breast feathers begin to form the broad ‘arrowead’ or ‘spearhead’ design that is prominent in the lower breast feathers.

Belly feathers: Are either white, bone white, or buffy with a gray base. Their extent (the visible area encompassed) varies among gender, age groups and islands. There is a slight tendency for males to have a “brighter” and less scaled center of the belly (more unpatterned feathers) than females, but this is not diagnostic by itself and should be used together with several other allometric and chromatic characters.

Undertail coverts: The undertail coverts have the same pattern as in Scaly-breasted Thrasher, but in Scaly-breasted the "arrowheads" tend to be thicker and browner, less white in their centers. The proximal half of the pearly-eye’s undertail feather vane has two concentric white-centered arrowheads and distal half of the vane is all white (ca 8–15 mm), depending on body size and age.

Uppertail coverts: Are variable among islands, depending on age and subspecies, but generally they are brown with white tips and a disparate amount of white (none to a few mm) centered along the rachis. While the white centers are on both sides of the rachis in some individuals, more often the white is limited to the anterior (outer) vein (pointing to rectrix 6 on either side). In HY/SY, the uppertail coverts are brown with no or little white in their centers. Also, the barbs are noticeably more widely spaced in juvenile-plumaged birds than in those already in their formative or basic plumages.

Photo Series – The link is a comparison of Pearly-eyed Thrasher body size, age and plumage characteristics exemplified in a hatch-year (HY) female (MCZ specimen no. 66457) and an after hatch year (AHY) female (MCZ specimen no. 66455) both collected 15 September 1914 by G. K. Noble on St. Croix, West Indies. All photos were taken by Jeremiah Trimble, Curatorial Associate, Ornithology, Museum of Comparative Zoology (MCZ), Harvard University.

Development — Hatchlings are naked and pink, their integument turning to a dark grayish purple within a few days as a result of visible, subcutaneous sanguineous veins. Young nestlings appear grayish overall with the emergence of gray body down and other feathers during the first prebasic (prejuvenile) molt in most feather tracts and their respective subregions: capital (and its three subregions), spinal (and its five subregions), alar (including its ca 10 each dorsal and ventral feather groups), caudal, femoral and crural tracts. In contrast, the feathers in the ventral tracts are beige to fawn. (See Arendt 1985 for nestling growth and ontogeny, i.e., a comparison of appendicular lengths by day and among hatch orders).

Because flight is the most important aspect of the majority of birds, I chose a feather in the alar tract to document feather growth in the pearly-eye. I selected the ninth primary because the tenth is modified and much reduced.

Graph Series– Two graphs and a table summarizing the emergence and growth of the ninth primary pin and the emergence from the ninth primary pin and growth of the rachis, which supports the feather’s vane (see Arendt 1985 for a discussion of primary 9 feather growth in relation to lay order and infesting philornid botfly larvae).

Molts

Pearly-eyed Thrasher follows the Complex Basic molt strategy.

The following cursory information is based on 60 individuals from 16 islands.

Island of Collection (MCZ Skins*) Total Collected Per Island Month Collected
Anguilla 2 February
Beata 1 April
Dominica 5 October (3), December (2)
Great Inagua 1 February
Guadeloupe 10 June (1), July (3), August (3), September (6)
Puerto Rico 1 April
Rum Cay (Bahama Islands) 1 February
St. Croix 7 April, September (6)
St. Eustatius 8 February (4), March (4)
St. John 2 February
St. Kitts 2 February, March
St. Lucia 5 December
St. Thomas 7 February
Tortola 4 March
Virgin Gorda 2 March
Wattlings Island 2 February

Of the 60 pearly-eyes examined, 28% showed signs of body and or flight feather molt. Whereas flight feather molt was noted only from June to September, body molt was observed in six separate months, which generally coincides (molt not documented as yet in May--by this observer) with the pearly-eye’s three breeding peaks during a 12-month period: 33% in March-April; 54% in May-June; and 3% in November-January. Percentages are based on the number of fledglings recorded in a Puerto Rican rain forest between 1979 and 2000 (n = 1,274).

It is anticipated that body and flight feather molt occur in other months and should be confirmed with the examination of more (live and museum) specimens.

Month Total Collected Each Month
January 0
February 20
March 11
April 3
May 0
June 1
July 3
August 3
September 9
October 3
November 0
December 7

Bare Parts

Iris – whitish to pearl white in adults, but can appear yellowish, depending on ambient lighting; dull brownish gray in juveniles and immatures.

Bill – Coloration varies more with age, less with gender. The bill is yellow in juveniles (young nestlings in natal down) and dark horn in immatures (older nestling having obtained their flight feathers) and adults. The bill tends to be, but not always is, lighter in adults. In some older individuals, the entire bill appears more yellowish than horn.

maxilla– darker at the base and culmenary ridge;

mandible – horn color, paler at the base;

Tarsi and toes – horn-colored in adults and immatures; footpads are yellowish. Tarsi and toes gray in juveniles.

Measurements

There are at least about 50 biological, geographical, climatic, and ecological influences governing body size of the Pearly-eyed Thrasher throughout its range. The more important factors are (in descending order) age, gender, elevation, season, and competition (see Arendt 2006a, Chapter 5, Figure 5.1, page 109).

Because of the pearly-eye's extensive geographic and altitudinal range, having been recorded on some 100 islands and cays and in diverse habitats from sea level to mountain summit within the Greater Caribbean Basin, its linear and volumetric measures vary significantly. Herein, only limited descriptive statistics will be included. For a more comprehensive review see Arendt 2006a (Chapter 5, pages 107–144) and Arendt 2006b (Appendix 4, pages 396–401).

Total Length: 20–30 cm (based on 60 pearly-eyes from 16 islands; see Molts for details)

The pearly-eye’s total length varies among age groups, gender, subspecies, altitude, and possibly latitude but a more thorough investigation is needed. The following information is cursory. More specimens must be compared before definitive conclusions can be drawn.

In museum skins measured from the tip of the beak to tail tip, total body length of adult pearly-eyes (AHY; n = 32; SE 0.186; 95% CI of the mean 0.378) was significantly longer than that of immature (HY/SY) birds (n = 28; SE 0.339; 95% CI of the mean 0.698; P 0.038) and also longer than hatch-year (HY) birds (n = 13; SE 0.476; 95% CI of the mean 1.047; P 0.014). However, HY birds were not significantly shorter than second-year (SY) birds (n = 15; SE + 0.423; 95% CI of the mean = 0.913):

There was no significant difference between the body lengths of adult males (AHY-M; n = 16) and adult females (AHY-F; n = 16). However, although there was also no significant difference between AHY males and immature males (HY/SY), adult females (AHY-F) were significantly longer than immature females (HY/SY-F; n = 14; P 0.012). Sample sizes were too small to compare HY and SY males or females:

Longitudinal measurements (in millimeters) – Descriptive statistics for eight appendicular characters (unflattened wing chord, exposed culmen, bill length from the nares, culmen depth, culmen width, tarsus, and tail [center rectrix]) taken from 1,251 live (mist-netted) thrashers from 14 islands are summarized below:

WING EXPOSCULM CULNARES CULDEPTH CULWIDTH PRIMARY9 TARSUS TAIL
AVERAGE 135.81 26.68 18.61 8.19 6.49 89.18 37.81 113.02
SD 4.94 2.13 0.97 0.44 0.63 4.16 1.75 4.67
MINIMUM – MAXIMUM 85.6 – 148 18 – 32.74 12.63 – 23.77 5.63 – 9.95 5.04 – 8.72 73.6 – 109.1 27.7 – 46.5 91 – 133

Body Mass (grams) – Generally, the pearly-eye’s body mass varies from ca 90 g near sea level to between 130 to 140 g at higher elevations. The subspecies M. f. klinikowskii inhabiting St. Lucia has, to my knowledge, the heaviest body mass on record (153 g), a nongravid (small ovaries) female collected by the late J. L. Gulledge (personal communication).

Descriptive statistics for body masses taken from 1,251 live (mist-netted) thrashers from 14 islands are summarized below. Data for both linear and volumetric (body mass) summaries are taken from Arendt et al. (2004):

BODY MASS
AVGERAGE 102.55
SD 10.24
MINIMUM – MAXIMUM 75.5 – 153

Subspecies Meristics – For the pearly-eye’s four subspecies, descriptive statistics taken on five appendicular characters (unflattened wing chord, tail [center rectrix], tarsus, exposed culmen, and bill length from nares) obtained from 584 museum skins collected on 37 islands, are summarized in Arendt (2006a: Appendix 4, Table 1, pages 396–401).

Of the pearly-eye’s three previously recognized subspecies (preceding the naming of a fourth, M. f. klinikowskii), the southernmost, M. f. bonariensis, is most distinct phenotypically. The five morphological characters described previously were included in a discriminant function analysis to compare body size among the three subspecies (Margarops fuscatus fuscatus, M. f. densirostris, and M. f. bonariensis). The most predictive variables showing the dissimilarity of M. f. bonariensis to the other two subspecies were, in descending order of importance, bill length from the nares, tarsus, and wing chord (similar to tail in importance). Because of a rich species diversity on Bonaire, sexual dimorphism is also most prominent in M. f. bonariensis (discussed in more detail in Arendt (2006a: Chapter 5, pages 119–142).

Middle toe and claw: 33.02 mm (Baird 1864–72).

Pearly-eyed Thrasher Pearly-eyed Thrasher (subspecies <em class="SciName">fuscatus</em>).
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Pearly-eyed Thrasher (subspecies fuscatus).
© Steve Tucker, Guánica, Puerto Rico, 05 Dec 2016
 Pearly-eyed Thrasher (subspecies <em class="SciName">fuscatus</em>).
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Pearly-eyed Thrasher (subspecies fuscatus).

Cruz Bay, Saint John Island, Virgin Islands. 19 January 2011.

© Stephen Davies
 Pearly-eyed Thrasher (subspecies <em class="SciName">bonairensis</em>).
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Pearly-eyed Thrasher (subspecies bonairensis).

Bonaire, ABC Islands, Leeward Antilles. 7 July 2006.

© Joe Tobias
 Pearly-eyed Thrasher (subspecies <em class="SciName">bonairensis</em>).
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Pearly-eyed Thrasher (subspecies bonairensis).

Bonaire, ABC Islands, Leeward Antilles. 5 July 2006.

© Joe Tobias
Pearly-eyed Thrasher Pearly-eyed Thrasher fledgling (subspecies <em class="SciName">fuscatus</em>)
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Pearly-eyed Thrasher fledgling (subspecies fuscatus)
© Sadhu Govardhan, Lajas, Puerto Rico, 19 Jan 2016
 Dorsal view comparison: HY-F/AHY-F Pearly-eyed Thrasher.
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Dorsal view comparison: HY-F/AHY-F Pearly-eyed Thrasher.

HY female: formative plumage. The light brown bases of the feather barbs in the crown and dorsum of the HY-F give it a cinnamon to rusty appearance overall. The secondaries and respective coverts are brown with russet to beige edgings and thin bone-white tips, evident in secondaries 8 and 9 (tertials 2 and 3). Although having somewhat more rounded flight feathers (tertials and rectrices with scant whitish tips) than HY Scaly-breasted Thrasher, the rectrices of this HY-F lack the broad shoulders and extensive white spotting as demonstrated by the AHY-F (photos A and B). AHY female: basic plumage. Note the rich, chocolate brown centers of the feathers in the crown and dorsum as well as the dark brown flight feathers, and the more extensive white tips in the remiges and broader white tail spots. Prebasic molt was noted in primaries 8, 9, 10 (2/3, 1/2, 1/3 grown, respectively), the remaining remiges were already replaced. Rectrix 6 was 1/2 grown and rectrix 5 was almost 2/3 grown. The remaining rectrices were already replaced. Prebasic molt was almost completed by 15 September. Museum of Comparative Zoology, Harvard University. 21 November 2011.

© Jeremiah Trimble
 Pearly-eyed Thrasher HY-F (left) and AHY-F (right) Rectrix Tips.
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Pearly-eyed Thrasher HY-F (left) and AHY-F (right) Rectrix Tips.

Close ups of the HY-F (left) and AHY (right) shown in photo. Note the narrow apices and the “L-shaped” white patterns in the posterior (inner) webbing in each rectrix of the HY-F (left), contrasting with the broad ‘shoulders’ at the apex of each feather vane in the AHY-F (right), and the somewhat more extensive white tips flowing down the inner webbing of each rectrix. Museum of Comparative Zoology, Harvard University. 21 November 2011.

© Jeremiah Trimble
 Ventral view HY-F/AHY-F Pearly-eyed Thrasher.
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Ventral view HY-F/AHY-F Pearly-eyed Thrasher.

Note the drabber and diffused upper breast feathers of the HY-F as compared to the more distinct, contrasting “spearheads” (scaled effect) of the AHY female’s upper breast feathers, together with the more extensive and much whiter feathers in the lower breast and abdomen. The color definition of the “spearheads” (brown borders, white centers), along with the brightness of the white feathers and the total area of the abdomen encompassed, are often greater in AHY males. The same rectrix shape and color patterns described previously are apparent in this ventral view. Museum of Comparative Zoology, Harvard University. 21 November 2011.

© Jeremiah Trimble
 Profile view HY-F/AHY-F Pearly-eyed Thrasher.
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Profile view HY-F/AHY-F Pearly-eyed Thrasher.

Visible once more in profile is the suffused, overall rusty appearance of the HY-F (bottom), its more diffused (“mousy”) upper breast feathers and lack of sharp contrast between less defined “spearheads” and more of a buffy abdomen. The more distinct, well-defined “spearheads” are visible in the AHY-F, especially along the flanks. Partially visible are the more extensive and whiter feathers in the lower breast and abdomen of the AHY-F, along with the darker (rich chocolate) alula and its covert, outer primary coverts, outer primaries 9 and modified primary 10. Museum of Comparative Zoology, Harvard University. 21 November 2011.

© Jeremiah Trimble

Recommended Citation

Arendt, W. J. (2017). Pearly-eyed Thrasher (Margarops fuscatus), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.peethr1.01