Cassia crossbill

The Cassia crossbill (Loxia sinesciuris) 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.

The species was first described in 2009, but only was accepted to be its own species in 2017, when it was found out to be phylogenetically distinct from the red crossbill, and its 10 unique call types.

The Cassia crossbill shares many physical features with the red crossbill and all of its different call types. Adult males display a brick red plumage along its crown, breast, and belly, while its flight feathers have a brown colour. In contrast, adult females have an overall dull green or olive-yellow colour, with brown flight feathers. Its defining feature, a crossed bill, is a crisscrossed bill used to access the pine cone seeds. However, in relation to the red crossbill call types, the Cassia crossbill has a deeper and thicker bill to crack open the harder pine cones in its habitat. Its body mass ranges from 29.2 to 43.9 g, while its wing length 85.0–100.0 mm and bill depth 8.90–10.56 mm.