Cassia Crossbill Life History

Habitat

Cassia Crossbills are year-round residents in Idaho's South Hills and Albion Mountains in the county that gives the crossbill its name. They tend to be more numerous in older and more open lodgepole pine forests.

Food

The Cassia Crossbill's crisscrossed bill is thicker than most Red Crossbills', allowing it to eat seeds from the Rocky Mountain lodgepole pine, a tree that produces a particularly tough pine cone. It bites down on the end of a cone, forcing the scales to open up. It then pushes its lower bill sideways to open the cone even more. Once the cone is open far enough the bird uses its long tongue to grab the seed inside. The seed isn't swallowed immediately though; it first needs shelling, which is done with a groove on the inside of the bird's mouth.

Nesting

Nest Placement

Nesting behavior has not been precisely determined for Cassia Crossbills, but it is likely very similar to Red Crossbills. Male and female Red Crossbills choose a spot in an evergreen tree 6–65 feet above the ground in an area with a lot of vegetation cover. Females do the majority of nest building, but the male occasionally brings a bit of material.

Nest Description

Female Red Crossbills and presumably Cassia Crossbills weave together small evergreen twigs to form a cup-shaped nest. They line the cup with grasses, hair, lichen, and needles.

Nesting Facts

Behavior

Cassia Crossbills share much of the same behavior as Red Crossbills. They both forage in large and vocal groups in search of good cone crops. They eat seeds from pine cones in the canopy, but also forage for seeds on the ground. Unlike Red Crossbills, Cassia Crossbills are not nomadic and they tend to breed at the same time every year. The breeding season begins in late March and early April in the South Hills and ends around late July. Males court females with a song and a flight above the forest canopy. Males continue courting females by feeding them pine seeds. Adults eat lodgepole pine seeds year-round and even feed seeds to their young. Parents regurgitate a paste of lodgepole pine seeds and saliva to feed their young until they are old enough to eat whole seeds.

Conservation

The recently described Cassia Crossbill is already vulnerable and at risk of extinction due to its small population size and geographic isolation. Populations declined by 60% between 2003 and 2008, and by another 80% by 2011. These declines could be due to higher spring temperatures that cause the lodgepole pine cones to open up prematurely and thus don't provide the year-round food source the crossbills rely on. Since 2011 populations have increased slightly, and researchers suggest that about 6,000 individuals occur in Cassia County. However, increases in fire frequency and intensity as well as infestations of mountain pine bark beetle threaten Cassia Crossbill habitat. Lodgepole pine in the South Hills is sensitive to climate change and researchers predict that those trees may disappear by the end of this century. Partners in Flight has yet to assess the conservation status of Cassia Crossbill, but given its restricted range and small population size, it likely rates a 16 out of 20 on the Continental Concern Score, placing it on the Yellow Watch List.

Credits

Adkisson, C. S. (1996). Red Crossbill (Loxia curvirostra), version 2.0. In The Birds of North America (A. Poole, Editor), Cornell Lab of Ornithology, Ithaca, New York, USA.

Benkman, C. W. (2016). The natural history of the South Hills Crossbill in relation to its impending extinction. American Naturalist 188:589-601.

Benkman, C. W., J. W. Smith, P. C. Keenan, T. L. Parchman, and L. Santisteban (2009). A new species of the Red Crossbill (Fringillidae: Loxia) from Idaho. Condor 111:169–176.

Neely, N. (2017). The West's newest bird species has a beak like a crowbar. High Country News 49:13.

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