A rare crossbill endemic to a tiny area of Idaho. Among the most range-restricted US bird species.

Also called: South Hills Crossbill

Native status: Native; near threatened; endemic to two Idaho mountain ranges

§ Quick facts

SizeBody 15–17 cm (5.9–6.7 in); wingspan 27 cm
Weight32–45 g — larger bill than other Red Crossbills
LifespanWild typically 5+ years
OrderPasseriformes
FamilyFringillidae

§ Encyclopedia

The Cassia crossbill is a passerine bird in the family Fringillidae. It is endemic to the South Hills and Albion Mountains in southern Idaho. Cassia crossbill rarely interbreeds with other call types that move into the South Hills of Idaho yearly, and can be considered to represent a distinct species via ecological speciation. The Cassia crossbill have specialized beaks to access the seeds of the lodgepole pine cones in this region, but are poorly adapted to other pine cones in surrounding regions.

Source: Wikipedia — Cassia crossbill Licensed under CC BY-SA 4.0

§ Identification

Field marks. Medium crossbill — males brick-red, females olive-yellow. Distinctive crossed mandible tips for prying open pine cones. Larger bill than other Red Crossbill types.

Similar species. Red Crossbill (other "call types" overlap visually; Cassia is genetically and acoustically distinct). White-winged Crossbill (white wing bars).

Voice. Distinctive flight call "kip-kip" lower-pitched than other Red Crossbill types.

§ Diet & behavior

Diet. Almost exclusively lodgepole pine seeds. Specialized bill geometry exactly matches the cone scales of South Hills lodgepole pine.

Behavior. Split as a distinct species in 2017 — exists ONLY in two small mountain ranges (Cassia and Albion) in south-central Idaho, on a total of ~70,000 acres. Coevolved with squirrel-free lodgepole pines: in the absence of squirrels (which usually open cones), the trees produced thicker, harder cones, and the crossbills evolved larger bills to crack them. One of the most extreme examples of bird-tree coevolution in North America. Habitat is highly vulnerable to fire and climate change.

§ Range

South Hills and Albion Mountains, Idaho

§ Habitat

Lodgepole pine forests

§ Threats

Climate change, habitat loss.

§ Conservation status

According to the IUCN Red List, the cassia crossbill is currently classified as Near Threatened.

§ What helps

Support South Hills and Albion conservation.

Support our work More ways to help

§ Further reading

§ Sources cited

  • USFWS Cassia Crossbill Profile
  • Cornell Lab — All About Birds
  • Sawtooth National Forest
  • IUCN Red List 2020