Red Warbler

Cardellina rubra

The Red Warbler (Cardellina rubra) is a small, vibrant passerine bird, a member of the New World warbler family Parulidae. This species is endemic to the highlands of Mexico, presenting a striking bright red plumage. Depending on the subspecies, the adult Red Warbler sports a distinctive white or gray ear patch. The juveniles are more subdued in color, with a pinkish-brown hue and a whitish ear patch, accented by two pale wingbars.

Identification Tips

Adult Red Warblers are unmistakable with their overall red coloration, darker dusky red wings and tail, and a characteristic ear patch that varies in color by subspecies. Their legs are a dull red-brown, and the bill is pinkish-gray with a dark tip. Females may appear slightly duller or more orange-tinged than males. Juveniles can be identified by their pinkish-brown plumage and the presence of two pale wingbars.

Habitat

The Red Warbler is found in the highlands of Mexico, preferring humid or semi-humid pine, pine-oak, and fir forests at elevations ranging from 1,800 to 3,900 meters above sea level. During the non-breeding season, they migrate to lower elevations, often in oak forests.

Distribution

This species is endemic to Mexico, with three disjunct populations corresponding to the three subspecies. They are found from southwestern Chihuahua to northern Nayarit, from southern Jalisco and southern Hidalgo to Oaxaca, and from Guerrero into southern Oaxaca in the Sierra Madre del Sur mountains.

Behaviour

Red Warblers are typically observed alone or in pairs, often remaining together year-round. They are not commonly found in mixed-species flocks. During the breeding season, males establish territories and engage in combat with intruders. The species is known for its altitudinal migration patterns.

Song & Calls

The Red Warbler's calls include a high, thin "tsii" and a stronger "pseet." Its song is a delightful mix of short trills and richer warbles, punctuated by high-pitched chips. Singing is most frequent during bright morning hours in the breeding season.

Breeding

Breeding occurs from February to May. The female constructs a domed nest on the ground, laying three to four eggs. She alone incubates the eggs, but both parents feed the young and remove waste from the nest. Fledging occurs within 10–11 days of hatching.

Diet and Feeding

An insectivore, the Red Warbler gleans primarily in understory shrubs, moving through vegetation with slow, deliberate movements. It employs a variety of foraging techniques, including hover gleaning and flycatching.

Conservation status

The Red Warbler is classified as Least Concern by the IUCN. Although its population is believed to be declining due to habitat destruction, the species is not currently facing a rapid decrease in numbers. However, the habitats it relies on are among the most threatened in Mexico.

Similar Species

The adult Red Warbler is unique in its range and unlikely to be confused with other species. The Scarlet Tanager and Summer Tanager may have similar red plumage but are larger with thicker bills.

Parasitism and Predation

The Red Warbler is vulnerable to predation by small hawks and nest raids by various mammals and reptiles. It is also host to the protozoan Isospora cardellinae, which inhabits its small intestine.