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Glaucidium brasilianum

Ferruginous Pygmy-Owl

  • Order: Strigiformes
  • Family: Strigidae
  • Polytypic 13 Subspecies

Authors: Larsen, Ray

Identification

Summary

Pygmy-owls (Glaucidium) are very small owls, with a large rounded head, a pair of prominent black marks (false "eye spots") on the nape, and a relatively long tail. Ferruginous Pygmy-Owl is the largest species of Glaucidium. The upperparts often are rufous ("ferruginous") but also may be duller grayish brown; the underparts are white, marked with broad streaks that are the same color as the upperparts. The crown also has fine white streaks.

Similar Species

All species of pygmy-owls are superficially similar in appearance, and often are distinguished most easily by voice (see Vocalizations), elevational preferences, and habitat. Due to its wide geographic range, the Ferruginous Pygmy-Owl overlaps with many other species of pygmy-owl. Ferruginous Pygmy-Owl can be distinguished from all members of the Least Pygmy-Owl group (Tamaulipas Pygmy-Owl G. sanchezi; Colima Pygmy-Owl G. palmarum; Central American Pygmy-Owl G. griseicepsSubtropical Pygmy-Owl G. parkeri; Amazonian Pygmy-Owl G. hardyi; Pernambuco Pygmy-Owl G. mooreorum; and Least Pygmy-Owl G. minutissimum) by its larger size, longer tail with a greater number of transverse pale buffy bars (5-7 bars on the upper surface of the tail, or 3-5 bars on the under surface of the tail, as opposed to 2-4 whitish bars on the tails of species in the Least Pygmy-Owl group), and by the presence of narrow pale streaks (not small pale spots) on the crown.

Ferruginous Pygmy-Owl also is similar to members of the Northern Pygmy-Owl group (Northern Pygmy-Owl G. gnomaCosta Rican Pygmy-Owl G. costaricanum; and Cloud-forest Pygmy-Owl G. nubicola), members of which are similar in size and shape to Ferruginous Pygmy-Owl, and may have a similar number of pale bars on the tail. As is the case with many members of the Least Pgymy-Owl group, all species in the Northern Pygmy-Owl group typically occur at higher elevations than Ferruginous Pygmy-Owl. These species also have small pale spots on the crown, not the narrow pale crown streaks of Ferruginous

In the Andes, Ferruginous Pygmy-Owl also overlaps geographically with Andean Pygmy-Owl (G. jardinii) and Yungas Pygmy-Owl (G. bolivianum), both of which also are similar in size and shape to Ferruginous, and both of which have a rufous morph. Both species typically occur at higher elevations than Ferruginous Pygmy-Owl, and in more humid and more closed forest. Adults of both species have small pale spots on the crown, but the crown of juveniles may be streaked, thus replicating the crown pattern of Ferruginous Pygmy-Owl. These juveniles are best distinguished from Ferruginous by voice, habitat, and elevation.

In southern South America, Ferruginous Pygmy-Owl is parapatric with Austral Pygmy-Owl (G. nana), which is very similar to (and perhaps only a subspecies of) Ferruginous. Austral Pygmy-Owl does not have a rufous morph, and the tail bars are pale rufous, not white.

Ferruginous Pygmy-Owl is very similar as well to Peruvian Pygmy-Owl (G. peruanum) of the lowlands of western Ecuador and Peru, and to semiarid intermontane Andean valleys. Ferruginous and Peruvian pygmy-owls are exceedingly similar to one another, although brown and gray morphs are much more frequent in Peruvian than in Ferruginous. These two species are allopatric; otherwise they best are distinguished by voice.

Vocalizations

The typical territorial/advertisement call of the male Ferruginous Pygmy-Owl is a repeated hoot. The notes are centered at around 620 Hz, and usually are given in a long series of 8-30 hoots evenly spaced at a speed between 150 and 200 notes per second (Proudfoot and Johnson 2000). The call is monotonal with no variation in pitch note-to-note. Between bouts of calling the Ferruginous Pygmy-Owl usually is silent for several seconds or more. The call is typically performed from a perched position, inclufing from habitual perches near the nest (Proudfoot and Johnson 2000). Ferruginous Pygmy-Owls respond readily to broadcasted calls (Flesch and Steidl 2007), and call significantly more often in response to solicited broadcasts than they do without solicitation (Proudfoot and Beasom 1996). When solicited, the calls are louder and more rapid than otherwise (Proudfoot and Beasom 1996, Proudfoot and Johnson 2000). Males tend to perform the territorial/advertisement call less often as nestlings develop (Proudfoot and Johnson 2000).

Although they don’t perform territorial/advertisement calls, females have alarm calls: two syllables in quick succession with an upward inflection. Males have not been recorded performing alarm calls and no anecdotal information is available. Females also “chitter” when receiving food and immediately before, during, and after copulation—a soft and short clucking sound. Juveniles beg for food with an even higher-pitched call that resembles a rattling sound (Proudfoot and Johnson 2000).

Additional recordings of Ferruginous Pygmy-Owl vocalizations can be heard at Macaulay Library and at xeno-canto.

Nonvocal Sounds

Ferruginous Pygmy-Owls sometimes snap their mandibles together to make a “beak clap” sound. The behavior is likely a sign of distress, as this bill snapping usually is reported during situations such as when the owl is handling or during nest inspection (Proudfoot and Johnson 2000).

Detailed Description (appearance)

Adult: Sexes similar, but occurs in several plumage morphs. In the rufous morph, upperparts generally are cinnamon rufous to rufous. The crown and nape have narrow longitudinal buff streaks. There is a broken white collar across the nape; the tips of the feathers on either side of the midline are tipped black, forming an oval black spot ("false eye"), enclosed by white, on each side of the nape. Tail rufous with 5-7 transverse paler bars. Lores and supercilium whitish. Throat white. Sides of breast rufous, almost meeting across the center. Belly white or whitish, broadly streaked with rufous. In other morphs, the general tone of the upperparts is duller brown or grayish brown; there are whitish or cinnamon buff spots on the scapulars and wing coverts; the outer webs of the primaries are spotted with buff and white; and the bars across the tail are white or whitish.

Juvenile: Similar to the adult, but crown lacks streaks, or streaks are greatly reduced.

Bare Parts

Iris: bright yellow

Bill and cere: light greenish yellow, sides of bill brighter green

Tarsi and toes: honey yellow

Bart parts color data from Wetmore (1968).

Measurements

Total length: 16-16.5 cm (Ridgely and Greenfield 2001), 16.5 cm (Hilty 2003), 16.5-19 cm (Howell and Webb 1995)

Linear measurements:

Data from Proudfoot and Johnson (2000); note that female are slightly larger than males.

bill length, males: mean 11.0 mm± 0.8; n = 291

                  females: mean 11.4 mm ±0.8; n = 186

wing length, males: mean 94.4 mm ± 4.4; n = 304

                  females: mean 98.7 mm ± 3.7; n = 194
tail length, males: mean 60.6 mm ± 4.0; n = 299

                  females: mean 63.6 mm ± 3.4; n = 188


Mass: male, mean 66.3 g ± 6.3; n = 20

            female. mean 73.0 g ± 7.9; n = 7 

In Texas, females may lose 15-20% of their mass during nesting, and males may lose 10-15% (Proudfoot and Johnson 2000).

Molts

Information very limited. In adults in Texas, tail molt occurs between mid July and late August when fledglings have mostly dispersed. Tail molts in Guatemala begins in late September or early August. Molting of primaries probably begins in July and ends in October, but no conclusive data exists. In fledglings in Texas, remiges and retrices achieve adult length by week 8 (Proudfoot and Johnson 2000).

Geographic Variation

Generally, northern populations appear to show somewhat longer wings and shorter tails (Proudfoot and Johnson 2000). Plumage coloration also shows some distributional variation: paler, more gray-toned plumage predominates in populations that occur in drier environments, while birds that live in moister environments typically display a brighter plumage (Proudfoot and Johnson 2000). The number of subspecies recognized varies from 12 (Dickinson 2003) up to 14 (Proudfoot and Johnson 2000):

ridgwayi: Range is central and south Mexico. Distinction between this subspecies and cactorum (see below) is slight.

cactorum: Range is south Arizona to Nayarit, Mexico. In comparison to ridgwayi, the wing is shorter, the tail longer, and the plumage paler and grayer.

intermedium: Range is Mexico from south Nayarit to south Oaxaca. Birds are paler than ridgwayi but darker than cactorum. Recognized by Proudfoot and Johnson (2000), but not by Peters (1940), Friedmann et al. (1950), Dickinson (2003), or König and Weick (2008).

saturatum: Pacific lowlands of Chiapas (District of Soconusco), Mexico, south into adjacent Guatemala. This subspecies is larger, darker above, and has more heavily streaked underparts than ridgwayi. Recognized by Proudfoot and Johnson (2000), but not by Peters (1940), Friedmann et al. (1950), Dickinson (2003), or König and Weick (2008).

medianum (north Colombia)

phaloenoides (north and east Venezuela, Trinidad, and Guianas)

margaritae (Venezuela)

duidae (Mt. Duida in south Venezuela)

olivaceum (Mt. Auyan-Tepuí, southeast Venezuela)

ucayalae (Amazon Basin from southeast Colombia, Venezuela, and Brazil to south Peru and north Bolivia)

brasilianum (northeast Brazil to northeast Argentina and north Uruguay)

pallens (east Bolivia, west Paraguay, and north Argentina)

tucumanum (northwest Argentina)

stranecki (central Argentina to south Uruguay)

Systematics

Until recently, the populations of Glaucidium in the lowlands of northwestern South America were classified as part of Glaucidium brasilianum brasilianum, which otherwise occurs only east of the Andes. These Pacific slope pygmy-owls now are recognized as a distinct species, Glaucidium peruanum (Peruvian Pygmy-Owl), primarily on the basis of different vocalizations (König 1991).

Questions remain regarding the species status of several other taxa in the brasilianum group. Proudfoot et al. (2006) proposed splitting Glaucidium brasilianum into two species based on mitochondrial DNA analysis and phylogeography. The researchers observed that populations in Arizona, Texas and Mexico are genetically distinct from populations in South America: they share no mitochondrial haplotypes, and have evidently no gene flow with South American populations (Proudfoot et al. 2006a; Proudfoot et al. 2006b). Similarly, Heidrich et al. (1995) and König and Wieck (2008) separate all North American taxa (south to northwestern Colombia) as Glaucidium ridgwayi (Ridgway's Pygmy-Owl), "on the basis of DNA evidence and vocalisations" König and Wieck (2008).

Subspecies tucumanum also has been recognized as a separate species (Heidrich et al. 1995); König and Weick (2008) include pallens in with tucumanum as well.

Most authorities (e.g. Peters 1940, Heidrich et al. 1995, Dickinson 2003, König and Weick 2008, Remsen et al. 2012) consider nana as a separate species (Austral Pygmy-Owl), but Marin et al. (1989) suggested that it may "merely represent a predominance of the darker rufous-brown morph" within brasilianum.

Recommended Citation

Larsen, Ray. 2012. Ferruginous Pygmy-Owl (Glaucidium brasilianum), Neotropical Birds Online (T. S. Schulenberg, Editor). Ithaca: Cornell Lab of Ornithology; retrieved from Neotropical Birds Online: http://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=212056