For example , the culmen of the parrot crossbill is strongly decurved , while that of the very similar red crossbill is more moderately curved .
The shape or color of the culmen can also help with the identification of birds in the field .
The culmen of the parrot crossbill is strongly decurved , while that of the very similar red crossbill is more moderately curved .
The shape or color of the culmen can also help with the identification of birds in the field .