ASN Address: “The natural history of the South Hills crossbill in relation to its impending extinction”

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Craig W. Benkman

A female South Hills crossbill foraging on the ground for seeds in a lodgepole pine cone. Cones that fall from trees open during hot summer days when in direct sunlight, and apparently this occurs for cones in trees during summers with four or more hot days (≥32°C).
(Credit: Craig W. Benkman)

Many newly discovered or yet-to-be discovered species are likely to be rare and range-restricted, and hence vulnerable to extinction. A newly discovered bird that may warrant species recognition is one such vulnerable species. It is confined to two small mountain ranges on the edge of the Great Basin Desert in southern Idaho. This bird, called the South Hills crossbill, is a type of finch with a crossed beak, specialized for removing seeds secured between the hard scales of lodgepole pine cones. Nearly all the cones in these two ranges remain closed for years until a high severity fire heats them, causing the seeds to be shed. As long as large parts of these mountains escape fire, seeds are plentiful enough in cones to support this distinct crossbill. Cone seed, however, might not be sufficient later in this century. Unusually hot summer days, which are projected to occur much more frequently with climate change, seem to mimic fire in causing cones to open and shed their seeds. Because shed seeds are no longer readily accessible or even used by South Hills crossbills, hot summer days diminish the suitability of the forests that escape fire. The population of South Hills crossbills recently declined by 80% following a series of hot summer days beginning in 2003, but has since rebounded to several thousand individuals following a hiatus in exceptional hot days. With climate change, however, this rebound—and the crossbill—may be ephemeral. Read the Article