Of the 10000 bird species on Earth, only five, all in the finch family, have crossed bills. The White-winged Crossbill is found in the higher latitudes of North America, traveling from coast to coast in large flocks in search of white spruce trees. Females are greenish yellow, males red, and both have two distinct white bars on the wings. Their unique crossed bill, with the lower mandible curving under the upper maxilla, is adapted to reach heavily protected seeds found under tough cone scales. To reach the seeds a White-wing places the tip of the curved lower mandible against the cone while inserting the upper maxilla under the scale. Beak partially open, the bird uses the curved mandible as a lever, twisting his head as he pries up the scale. He eats the seed, discarding the husk. The curve of the mandible provides the leverage needed to force the scale up, enabling crossbills to feed on seeds that are not accessible to other species. A White-wing often twists the cone off, and carries it to a perch, where it holds the cone in one claw and rotates it like a corncob. Lower mandibles cross either left or right, and each individual always holds the cone in the claw toward which their mandible curves. This ensures that the tip of the mandible is facing the cone, giving the bird the best leverage to quickly pluck the seeds. White-wings are remarkably efficient at harvesting their food. An individual bird can eat up to 3000 seeds per day. Crossbills are able to swiftly bypass a conifer’s armor as a direct result of their specialized beaks, an excellent example of evolutionary adaptation.

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The average White-winged Crossbill can eat up to 3,000 seeds per day. How can one bird get access to so much food? The answer lies in the structure of this bird’s unique crossed bill. This physical adaptation grants the White-winged Crossbill access to seeds from pine cones that other species with ordinary bills simply can’t get to. The crossed bill acts as a barrier to species competing for food within the same habitat. What appears at first to be an abnormality is in fact extremely advantageous.

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