Bay-ringed Tyrannulet Phylloscartes sylviolus Scientific name definitions

One of a suite of generally rare Phylloscartes tyrannulets endemic to the Atlantic Forest region, the Bay-ringed Tyrannulet is a canopy dwelling species found from southeastern Brazil south to easternmost Paraguay and northeastern Argentina. It is moderately distinctive in being rather clean white over the underparts and bright yellowish olive above, with no obvious wing bars, and with a distinctive face pattern consisting of yellow ear coverts and a rufous-chestnut eye surround. However, seeing the bird well enough to discern all of these features can be difficult! Like many other congenerics, the Bay-ringed Tyrannulet regularly joins mixed-species flocks, but many aspects of its life history remain to be elucidated, although the species’ nest has been described.

The Bay-ringed Tyrannulets have 10 full-length primaries (numbered distally, from innermost p1 to outermost p10), 9 secondaries (numbered proximally, from innermost s1 to outermost s9 and including 3 tertials, s7–s9 in passerines), and 12 rectrices (numbered distally from innermost r1 to outermost r6 on each side of the tail). Little or no geographic variation in plumage has been reported (see Systematics); the following descriptions are based on those of Ridgely and Tudor (1 Ridgely, R. S., and G. Tudor (1994). The Birds of South America. Volume 2: The Suboscine Passerines. University of Texas Press, Austin, TX, USA. Close ) and Fitzpatrick et al. (2 Fitzpatrick, J. W., J. M. Bates, K. S. Bostwick, I. C. Caballero, B. M. Clock, A. Farnsworth, P. A. Hosner, L. Joseph, G. M. Langham, D. J. Lebbin, J. A. Mobley, M. B. Robbins, E. Scholes, J. G. Tello, B. A. Walther, and K. J. Zimmer (2004). Family Tyrannidae (tyrant-flycatchers). In Handbook of the Birds of the World. Volume 9 (J. del Hoyo, A. Elliott, and D. A. Christie, Editors), Lynx Edicions, Barcelona, Spain. pp. 170–462. Close ), along with examination of Macaulay Library images; see Pyle (3 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ) for criteria used for age and sex determinations of similar tyrannid flycatchers. See Molts for molt and plumage terminology. Sexes are similar in all plumages; definitive appearance is assumed at the Second Basic Plumage. Timing of plumages relates to timing of molts, which appears to peak primarily in December-February following a reported extended breeding season in August-December (see Breeding Phenology and Molts).

Natal Down

Occurs in the nest, perhaps primarily in September-December. No information on natal down in Bay-ringed Tyrannulet but in the congeneric Mottle-cheeked Tyrannulet (Phylloscartes ventralis) nestlings are covered with sparse gray natal down.

Juvenile (First Basic) Plumage

May occur primarily in October-February. Based on a Macaulay image (if correctly identified; see below) it appears to be similar to later plumages but body feathering is duller. Crown and upperparts washed gray; underparts pale gray to whitish washed dull yellow or olive and with diffuse olive streaking. The bay coloration around the eye appears to be absent. Juvenile body feathering is more filamentous than that of later plumages due to lower barb densities. Juvenile flight feathers are narrower and more pointed than later generations and are fresh at a time of year when older birds are typically worn and/or molting. Juveniles also appear to have a dark iris, perhaps lightening to amber (see Bare Parts).

Formative Plumage

Appears to occur primarily in February (when fresh) to December (when worn). Examination of Macaulay Library images indicates that the Preformative Molt is partial and that Formative Plumage is identified by molt limits among wing and perhaps occasionally tail feathers. Most to all upperwing lesser coverts, some to most inner median coverts, and no to a few inner greater coverts may be replaced and are fresher and greener, contrasting with the more worn and browner, retained juvenile outer secondary coverts, and primary coverts which show little or no olive edging. Look for 1-2 inner tertials (among s8-s9) and 1-2 central rectrices also to be replaced and contrastingly fresh. Retained juvenile outer primaries and rectrices are narrow, tapered or pointed at the tips, abraded, and brownish. Formative Plumage may also average duller than Definitive Basic Plumage, with a paler yellow chin and malar region and a less distinct bay eye patch. The iris also appears to transition from dark to white while in Formative Plumage (see Bare Parts).

Definitive Basic Plumage

Appears to occur primarily in March (when fresh) to December (when worn). Upperparts and crown bright olive; prominent loral patch and eyering rufous-chestnut; post ocular feathers and auriculars olive above, lacking much contrast with the dark eye patch, but bordered below by pale yellow lower auriculars and malar region. Upperwing coverts, remiges, and recrtices from above dusky edged olive, the greater coverts fringed pale yellow forming an indistinct wing bar. Chin yellow, sometimes fading to paler yellow on throat; rest of underparts whitish (when fresh) to white (when worn), often tinged greenish dusky on the sides of the breast (sometimes including a diffuse band that separates the throat) and the flanks, and/or with a very slight yellow tinge down the mid belly when fresh, and with pale yellow to yellow undertail coverts.

Distinguished from Formative Plumage by having wing and tail feathers uniform in quality, lacking molt limits among upperwing coverts. Primary coverts are black to blackish, edged olive, and forming a distinct black triangular patch not contrasting in quality of coloration with the bases of the greater coverts (caution that the basic greater alula can sometimes be naturally slightly browner in this species, creating a pseudolimit). Outer primaries and rectrices are broader, more truncate, duskier, and relatively fresher than retained juvenile feathers of Formative Plumage. The iris also is typically bright white for birds in Definitive Basic Plumage (see Bare Parts).

General

Molt and plumage terminology follows Humphrey and Parkes (4 Humphrey, P. S., and K. C. Parkes (1959). An approach to the study of molts and plumages. Auk 76(1):1–31. Close ) as modified by Howell et al. (5 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close ). Little has been published on molts in Bay-ringed Tyrannuletbut, based on examination of Macaulay Library images, this species appears to exhibit a Complex Basic Strategy (cf. 5 Howell, S. N. G., C. Corben, P. Pyle, and D. I. Rogers (2003). The first basic problem: a review of molt and plumage homologies. Condor 105:635–653. Close , 6 Howell, S. N. G. (2010). Peterson Reference Guide to Molt in North American Birds. Houghton Mifflin Harcourt, Boston, Massachusetts, USA. Close ), including complete prebasic molts and a partial-to-incomplete preformative molt, but no prealternate molts. Other tyrannid flycatchers can also undergo limited prealternate molts, that may include scattered body feathers and the tertials (3 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ), but there is little evidence for this among Macaulay Library images of Bay-ringed Tyrannulet. Most molting appears to occur in December-February, following breeding primarily in August-December, as based on examination of Macaulay Library images (see below).

Prejuvenile (First Prebasic) Molt

Complete, in the nest, primarily in November-January. No information on juvenile feather development in Bay-ringed Tyrannulet .

Preformative Molt

Examination of Macaulay Library images indicates that the Preformative Molt is partial, including body feathers, most to all upperwing lesser coverts, some to all median coverts, and no to some greater coverts, but no primaries, primary coverts, secondaries or rectrices; look for 1–2 tertials (s9, s8, or s8-s9) or central rectrices (r1) to occasionally be replaced, as can occur in other Phylloscartes tyrannults that typically replace more secondary coverts. See images under Formative Plumage. It appears to occur primarily in November-January, 1-2 months following fledging at the individual level.

Definitive Prebasic Molt

Complete, perhaps primarily in December-March, 1-3 months following breeding at the individual level. Primaries (and corresponding primary coverts) are replaced distally (p1 to p10), secondaries are replaced proximally from s1 and proximally and distally from the central or innermost tertial (s8 or s9), as is typical in passerines, and rectrices appear to be replaced distally (r1 to r6) on each side of tail, with some variation in sequence possible.

The following is based primarily on examination of Macaulay Library images. See also images under Plumages.

Bill and Gape

The bill is relatively narrow and sharply pointed for a tyrannid flycatcher. At all ages it is black. In juveniles the base of the lower mandible may be pinkish; this color or ashy may remain at the extreme base in adults, but this is rarely visible in the field.

Iris

In adults the iris is bright white. In nestlings and juveniles it appears to be darker in color, perhaps typically dark amber. Iris color appears to lighten during the first few months of life, becoming whitish washed brown, then tinged brown, and becoming dull to brightish white in at least some birds by a year of age (see image below and those under Formative Plumage). Iris color change by age appear to parallel that of White-eyed Vireo (Vireo griseus); in this species occasional older birds can retain dark irises (3 Pyle, P. (2022). Identification Guide to North American Birds. Part I, Second Edition. Slate Creek Press, Forest Knolls, CA, USA. Close ) but there is as yet no evidence for this in Bay-ringed Tyrannulet.

Tarsi and Toes

At all ages the legs and feet vary from bluish gray to slate.

Linear Measurements

Overall length 12 cm.

Mass

Ca. 8 g.

Long placed in a monotypic Leptotriccus, but seems to be typical member of present genus. May belong with the “P. flaviventris group” (which see).

Monotypic.

Eastern Paraguay (Canindeyú south to Itapúa), southeastern Brazil (southern Minas Gerais and Espírito Santo south to Santa Catarina) and northeastern Argentina (Misiones).

Humid lowland and foothill evergreen forest and forest edge, to 600 m.

Microhabitat for Foraging

Forages predominantly in forest canopy, often in company of mixed species flocks.

Food Capture and Consumption

Active and restless while foraging, holding body horizontally with long tail cocked above horizontal and wings often held out or drooped. Makes short sallies to snatch or hover-glean insects from branches and leaves, rarely from air; occasionally reaches to pick insects from leaf surfaces. Forages alone or in pairs, occasionally in family groups of 3–5 birds.

Major Food Items

Insects (including Odonata) and small fruits (7 Sigrist, T. (2005) Aves do Brasil: Uma Visão Artística. Author's edition, Vinhedo. Close , 8 Rodrigues, R. C., H. F. P. Araujo, R. M. Lyra-Neves, W. R. Telino-Júnior, and M. C. N. Botelho (2007). Caracterização da Avifauna na Área de Proteção Ambiental de Guadalupe, Pernambuco. Ornithologia 2: 47–61. Close ).

Vocal Array

Song is a fast, complex series of high notes, swit-swi-swi-swi-swi-deedeedeedee-swi-swi.

Degree of Sociality

Typically observed alone or in pairs, occasionally in family groups of 3–5 birds.

August–October in Argentina; adults with fledged young in February, in Brazil and Paraguay (9 Kirwan, G. M., A. Bodrati, and K. Cockle (2010) The nest of the Bay-ringed Tyrannulet (Phylloscartes sylviolus), a little-known Atlantic Forest endemic, supports a close relationship between Phylloscartes and Pogonotriccus. Ornitología Neotropical 21: 397–408. Close , 2 Fitzpatrick, J. W., J. M. Bates, K. S. Bostwick, I. C. Caballero, B. M. Clock, A. Farnsworth, P. A. Hosner, L. Joseph, G. M. Langham, D. J. Lebbin, J. A. Mobley, M. B. Robbins, E. Scholes, J. G. Tello, B. A. Walther, and K. J. Zimmer (2004). Family Tyrannidae (tyrant-flycatchers). In Handbook of the Birds of the World. Volume 9 (J. del Hoyo, A. Elliott, and D. A. Christie, Editors), Lynx Edicions, Barcelona, Spain. pp. 170–462. Close ).

Site Characteristics

Nests are sited between 10 and 25 m above the ground (10 Narosky, S., and S. A. Salvador (1998). Nidificación de las Aves Argentinas: Tyrannidae. Asociación Ornitológica del Plata, Buenos Aires, Argentina. Close , 2 Fitzpatrick, J. W., J. M. Bates, K. S. Bostwick, I. C. Caballero, B. M. Clock, A. Farnsworth, P. A. Hosner, L. Joseph, G. M. Langham, D. J. Lebbin, J. A. Mobley, M. B. Robbins, E. Scholes, J. G. Tello, B. A. Walther, and K. J. Zimmer (2004). Family Tyrannidae (tyrant-flycatchers). In Handbook of the Birds of the World. Volume 9 (J. del Hoyo, A. Elliott, and D. A. Christie, Editors), Lynx Edicions, Barcelona, Spain. pp. 170–462. Close , 9 Kirwan, G. M., A. Bodrati, and K. Cockle (2010) The nest of the Bay-ringed Tyrannulet (Phylloscartes sylviolus), a little-known Atlantic Forest endemic, supports a close relationship between Phylloscartes and Pogonotriccus. Ornitología Neotropical 21: 397–408. Close ).

Construction

Both parents build the nest (9 Kirwan, G. M., A. Bodrati, and K. Cockle (2010) The nest of the Bay-ringed Tyrannulet (Phylloscartes sylviolus), a little-known Atlantic Forest endemic, supports a close relationship between Phylloscartes and Pogonotriccus. Ornitología Neotropical 21: 397–408. Close ).

Structure and Composition

Hanging nest (see photo 1, and photo 2) with lateral entrance hole, composed mainly of moss and suspended below a horizontal branch.

Clutch Size

Undescribed.

Color and Surface Texture

Egg clean white (9 Kirwan, G. M., A. Bodrati, and K. Cockle (2010) The nest of the Bay-ringed Tyrannulet (Phylloscartes sylviolus), a little-known Atlantic Forest endemic, supports a close relationship between Phylloscartes and Pogonotriccus. Ornitología Neotropical 21: 397–408. Close ).

Not globally threatened. Currently considered Near Threatened. Uncommon to scarce.

Conservation Areas

Occurs in several protected areas, in Brazil including e.g., Iguaçu National Park and Mata dos Godoy State Park (both in Paraná), and Intervales State Park (São Paulo), where rarely observed around Saibadela Research Station but more abundant at upper elevations within the park; in Argentina, regular in forests near Iguazú Falls in Iguazú National Park; and in Paraguay, uncommon at Estancia Itabó Private Nature Reserve, Mbaracayú Forest Nature Reserve, and Caaguazú and San Rafael National Parks.

Conservation Measures and Habitat Management

Atlantic Forest continuously threatened by agricultural conversion, mining, urbanization, industrialization, and associated road-building.