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Camptostoma imberbenorthern beardless tyrannulet(Also: northern beardless-tyrannulet)

By Secorra Denny

Geographic Range

Camptostoma imberbe is found in North and Central America, in a range encompassing the southern United States to Costa Rica. During the breeding season, this range encompasses southeastern Arizona, a small southwestern corner of New Mexico, and the southern tip of Texas, continuing south through Mexico, through Central America, and reaching into the northwestern region of Costa Rica.

During the winter season, the Northern Beardless Tyrannulet resides in the northernmost portion of the range, particularly the southwestern USA. Due to this, it can be considered a short-distance migrator. They typically move from higher to lower populations, or to a slightly more southern region than their breeding range. However, at this time, Camptostoma imberbe is not considered a migratory bird, and is considered to be a resident of the breeding range. The Northern Beardless Tyrannulet has been found in the northernmost regions, indicating that individuals of this species are resident to their typical breeding grounds. Camptostoma imberbe vocalize less than other birds and can wander from its breeding sites during the winter, which causes a lack of information regarding its migratory behaviors, if they exist. (Schuyler, 2004; Tenney, 2000)

Habitat

The Northern Beardless Tyrannulet is found throughout the southwestern United States to as far south as Costa Rica. Within this range, the Camptostoma imberbe is found at lower elevations, from sea level to 2,100 m. This region can be arid to semi humid. They are typically found in low woods, mesquite, semiopen brushy woodlands, scrubby thickets, forest edges, and riparian regions, such as those that are near a river, or dry washes in the arid regions. (Schuyler, 2004; Tenney, 2000)

  • Range elevation
    0 (sea - level) to 2,100 m
    to ft

Physical Description

The Camptostoma imberbe is a small, plain colored songbird. The length of this bird ranges from 9.5 to 11.5 cm, and has an average mass of 7.5 g. The upper parts of this bird is grayish olive in color, while its crown and nape are a darker color, typically gray. Its wings are blackish in color, and has dull white to buff wing bars and edges on its tertiary and secondary wing feathers. Its breast feathers are grayish-olive in color, with a paler throat and an oftentimes pale yellow tinged belly. Its legs can be dark brown, blackish brown, or dull grey in color. Its bill is short, narrow, and curved, with a black upper beak and a lower beak that is creamy pink at the base, which gradually darkens towards the tip. Males and females have not been seen to have notable differences in length, mass, or plumage. However, males are known to possess longer wings and tails than females. The average wingspan for males is 47 – 62 cm in length, and its tail length for males is 35 - 52 cm. In contract, the female's wingspan is 46-56 cm, and their tail length is 33 - 46 cm. (Schuyler, 2004; Tenney, 2000)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    7.5 g
    0.26 oz
  • Range length
    9.5 (low) cm
    3.74 (low) in
  • Average length
    11.5 cm
    4.53 in
  • Range wingspan
    Male 47 , Female 46 (low) cm
    (low) in
  • Average wingspan
    Male 62, Female 56 cm
    in

Reproduction

The Northern Beardless - Tyrannulet is a monogamous, sexually monomorphic bird. Sexually monomorphic refers to the lack of variation between the male and female in terms of plumage and size, aside from genitalia. Little information is known about the location, attraction, or defense of mates. The lack of information regarding the reproductive and other behaviors of the Camptostoma imberbe are likely due to its small size and its difficult to track behavior. Due to this, there is no knowledge regarding the social structure of this bird, or its mating system. Camptostoma imberbe is often found single in the winter, so it is thought that the selection of mates occurs after the start of territorial song season, which begins in early March in Sonora, Mexico and in Arizona. (Schuyler, 2004; Tenney, 2000)

The bird Camptostoma imberbe is oviparous, indicating that it gives birth to eggs, from which their offspring emerge. The breeding season varies throughout its habitat. In the southernmost portion of their range, the breeding season is March through June. In the northernmost portion, it varies depending on year; however, it usually falls from mid to late March through early August to late September. This variation is the result of variations in rainfall. In a single breeding season, the Northern Beardless - Tyrannulet is thought to have multiple broods of offspring, usually two to three. The number of brood increases when the spring and summer seasons are lengthened. Additionally, an earlier first brood date allows for more broods in the breeding season. An earlier first brood date is seen commonly in lower elevations. It should be noted that the number of broods in a particular breeding season varies regionally.

The amount of eggs that are in a clutch for Camptostoma imberbe ranges from one to three. However, the average is two eggs per clutch. The egg is oval or elongated oval in shape, and is usually cream in color with fine brown, reddish-brown, or gray speckling, which are located on the wider range. The surface of the egg is smooth and nonglossy, and the average size of an egg is 17.0 by 12.2 mm. The eggs are laid then incubated by the female. The female is the only parent that incubates the eggs, as only females have a brood patch. The incubation period is not known, however it has been estimated to be around 14 – 16 days.

The birth mass for the Northern Beardless - Tyrannulet is unknown. The newborns are hatched naked and flesh colored, with their eyes closed. The growth and development of young Camptostoma imberbe is not known. The lack of information on the young of this species is likely the result of their protective parents. The length from the time of hatching to departure of the nest is not well documented. It has been documented from a single brood that the length of time from hatching to fledgling was 12 days for a brood in Texas in 1999. The manner of departure is unknown, however it has been observed that two young birds showed the capability to fly on consecutive days.

There is no information on the length of time until the Camptostoma imberbe is independent. Additionally, there is a lack of information regarding the age of sexual maturity in either males or females. (Schuyler, 2004; Tenney, 2000)

  • Breeding interval
    The breeding interval for the Northern Beardless - Tyrannulet may vary regionally. It is estimated that they have two to three broods in northern populations, especially when the breeding season is extended.
  • Breeding season
    The breeding season is from March through June in the southern area of their habitat range. In the northern region of their habitat range, the breeding season for Camptostoma imberbe is from mid to late March through early August to late September.
  • Range eggs per season
    1 to 3
  • Average time to hatching
    14-16 days
  • Average fledging age
    12 days

The tyrannulet in Northern Beardless- Tyrannulet derives from “tyrant”, which refers to its aggressive behavior towards potential small predators of their young or eggs, and its overall highly protective care of its offspring.

The female Camptostoma imberbe is for the building of the nest, as such, the nesting site is likely to be chosen by the female. The nests are generally round or domed in shape, and are well concealed using a variety of nesting materials, such as spider webs, dead leaves, fine grasses, and seedpods. Additionally, only females have been reported to brood, and only female possess a brood patch. The male feeds and perches near the nest where the female incubates the eggs.

Once the offspring hatch, both parents tend to the young. Additionally, both parents display protective, aggressive behavior towards potential invaders. When a potential intruder gets too close to the nest of eggs or hatch-lings, both parents have been reported to ruffle their head-feathers, piping calls, and perched near the nest, within 1 meter. (Schuyler, 2004)

Lifespan/Longevity

The lifespan and longevity is not well documented in Camptostoma imberbe. The longest lifespan recorded was 5yrs, 9 mo. The reported factors of longevity for this species are likely predation, nest failure due to heavy rains, and possibly loss of habitat due to slight deforestation. (Schuyler, 2004)

  • Range lifespan
    Status: wild
    69 (high) months

Behavior

The Northern Beardless Tyrannulet is a shy species that lives either singly or in mating pairs. Due to the solitary nature of this bird, there is no known social hierarchy or structure. During the breeding season, the mated pairs are solitary, while in the non-breeding season the Northern Beardless Tyrannulet is typically found as a single individual. It has been noted that in the winter, this bird may follow mixed-species flocks, usually composed of titmice, warblers, and vireos, potentially for protection from predation. Individual breeding pairs have been noted on separate occasions to drive away a Lucy’s Warbler, Tufted Titmouse, and a House Sparrow, ignoring a Vermillion Flycatcher, while another pair was chased away by a Vermillion Flycatchers. The breeding system of this species is not well known. For more information, see the section(s) regarding reproduction.

This small bird is mobile and capable of flight. It often moves deliberately, in a manner that is very similar to vireos. Its tail often wags up and down when hopping and flitting through foliage, as well as when perching. In flight, it makes short, vertical flights when chasing flying insects, especially during summer time. The Camptostoma imberbe is known to occasionally hover when approaching the nest or getting food.

Camptostoma imberbe typically perches below canopy forage, and spends the majority of its time being quiet and unobtrusive. The tyrannulet is noted to perch upright, push out its chest, nervously flick its tail and perform double-wing flicks, and this set of behaviors typically occurs between insect eating’s or following foraging. However, it is known to vocalize.

The majority of the Northern Beardless Tyrannulet behaviors are unknown or based off of singular observations, because of the unassuming and inconspicuous behavior and diminutive size. The attributes make it difficult to study this shy bird. (Schuyler, 2004; Tenney, 2000)

Communication and Perception

The senses that are specially developed in the Camptostoma imberbe are not specifically well known, as are its forms of social communication. However, there are some observations regarding the communication between breeding, monogamous pairs.

Between potential mates, the Northern Beardless Tyrannulet has been observed to exchange multiple contact trills before mating and when they reunite after a period of time separated. The adults have been observed to elevate its crest when agitated by an intruder in the form of a human near its nest.

There are multiple vocal communications that this tyrannulet performs. It should be noted that the social context of said songs are not entirely known. More research is needed before a conclusion can be drawn.

The first is the “typical song”. The “typical song” can be phonetically described as "ee-ee-ee..", with each note being clear, whistled, and the song is loud, slow, and descends somewhat in pitch through the song. It is performed usually by males, but females have been reported to perform it. The male is noted to sing this during the day. It has been observed that this song is given from multiple locations and perches, and can be given from a significant distance of its nest, and is usually given after foraging for food. Its performance from multiple locations may indicate a territorial context.

During the breeding season, males give a “dawn song” during the predawn, from a typically lofty branch. This behavior may serve to claim his territory, or alert others to his nest location. This song possess a slow first phase with one to five notes, then a secondary phase of louder, quickly delivered notes. Males sing the dawn song thirty or more times without stopping, then switch to a typical song. The frequency of his typical song is slowly given less frequently as the day progresses, and individuals are generally quieter towards sunset as compared to earlier in the day.

The Northern Bearded Tyrannulet has general calls that are a slightly musical and less sharp version of the "pee" note present in both the Dawn and Typical songs. The function of the call is not described.

The female Camptostoma imberbe is noted to give the "Pee-uk" call, especially during breeding season. It is a short call that ends with a sudden frequency drop, which is heard as the "uk" noise, and is typically a singular call. Females are observed to give this call while they are foraging in multiple locations, but not up to the greater distance from the nest when compared to males.

One call that may have an agonistic function, as it was observed to be a response to a Dawn Song, was the "Peeeeeu" call. This is slightly longer and slurs downward when compared to the "Pee-uk" or "pee" notes, and is likely given by both sexes.

The tyrannulet also trills, and has been noticed to trill in a few instances. Females may trill a few notes between "Pee-uk" notes, and occasionally trill after foraging. In mating, the male trills before mating, and the trill may be traded after the pair has been separated after a period of time, potentially meaning the trill may serve as a greeting call.

The last call to be noted is the "bee-bee" call, which is a soft, 1-2 note call given by nestlings and fledgling. This may serve as a begging function, as it is often given when they are fed by either parent. (Tenney, 2000)

Food Habits

The Northern Beardless Tyrannulet primarily eats flying insects. They are noted to consume small berries, seeds, scaled insects, caterpillars, ants, and spiders. The tyrannulet forages in both high and low areas, and are generally found in mesquite or other small tress during this. During the summer, they use the top branches to catch flying insects, and forages for other food sources in the lower branches and bushes. They have also been noted to use bark and ball moss as locations to grab their food. Their beak is thin and pointed, which can be used similarly to tweezers to capture their food. The Camptostoma imberbe typically moves quickly while foraging, and is even noted to make short flights in summer to capture flying prey. However, flying foraging is less common when compared to other species in its taxonomic family. It may also hover or fly shortly upwards to forage for vegetation and other foods. (Schuyler, 2004; Tenney, 2000)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

The predation of this species is not well known, outside of a few distinct observations. One individual was found to be consumed by a Bat Falcon, Falco rufigularis, and snakes are known to steal eggs from the close relative, the Southern Beardless Tyrannulet, which produces a similar shaped nest to the Northern Beardless Tyrannulet. It is also implied through its behavior that hawks are a predator.

Two anti-predation behaviors have been noted. When a human gets too close to its nest, both males and females are noted to ruffle its head feathers and vocalized in a close range. In comparison, it freezes and crouches down onto a branch when a hawk flies over. Additionally, it could be noted that its diminutive size and shy behavior, which makes it difficult to study, may help prevent predation.

The general appearance of its plumage may help with camouflage with its surrounding, as it does not have bright colors. See the general appearance section for more information. (Tenney, 2000)

  • Known Predators
    • Bat Falcon

Ecosystem Roles

The ecosystem roles of this species are not very well known. However, it is the prey of larger, predatory birds, such as the Bat Falcon, or hawks. Additionally, their eggs may serve as food for snakes. The tyrannulet is mostly an insect predator, but is also noted to eat vegetation and seeds. The consumption of berries and seeds helps to impact the ecosystem by dispersing seeds. (Schuyler, 2004)

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

The positive economic importance for humans is not known. (Schuyler, 2004)

Economic Importance for Humans: Negative

The negative economic importance for humans is not known. (Schuyler, 2004)

Conservation Status

According to the IUCN, its conservation status is at the least concern, with its population increasing and parts of its range is conservation lands for other species, which also helps the tyrannulet. (Birdlife International, 2016)

Contributors

Secorra Denny (author), Colorado State University, Kate Gloeckner (editor), Colorado State University, Galen Burrell (editor), Special Projects.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

aposematic

having coloration that serves a protective function for the animal, usually used to refer to animals with colors that warn predators of their toxicity. For example: animals with bright red or yellow coloration are often toxic or distasteful.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

saltatorial

specialized for leaping or bounding locomotion; jumps or hops.

scrub forest

scrub forests develop in areas that experience dry seasons.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

terrestrial

Living on the ground.

visual

uses sight to communicate

References

Birdlife International, 2016. "Camptostoma imberbe" (On-line). The IUCN Red List of Threatened Species. Accessed March 26, 2019 at http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22699177A93717756.en.

Schuyler, T. 2004. Tyrant Flycatchers (Tyrannidae). Pp. 269-289 in M Hutchins, A Evans, J Jackson, D Kleiman, J Murphy, D Thoney, eds. Grzimek's Animal Life Encyclopedia, Vol. 10: Birds III, 2 Edition. Detroit, MI: Gale. Accessed February 26, 2019 at http://link.galegroup.com.ezproxy2.library.colostate.edu/apps/doc/CX3406700649/GVRL?u=coloradosu&sid=GVRL&xid=b0426761..

Tenney, C. 2000. "Northern Beardless-Tyrannulet (Camptostoma imberbe)" (On-line). Birds of North America. Accessed February 26, 2019 at https://doi-org.ezproxy2.library.colostate.edu/10.2173/bna.519.

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