Data from: Individual diet differences in a molluscivore shorebird are associated with the size of body instruments for internal processing rather than for feeding

Especially in birds, it is widely found that the size of individual prey
items follows the size of the instruments of prey capture, handling and
processing, i.e. bill size. In fact, this is the natural history basis of
major discoveries on adaptative evolution in the face of changing food
resources. In some birds, e.g. the molluscivore shorebirds ingesting
hard-shelled prey, most of the prey processing process takes place within
the digestive tract. This study of a salvaged sample of actively feeding
great knots Calidris tenuirostris accidentally drowned in fishing nets in
northern China, is the first documentation of diet selection at the level
of the individual in previously well-studied molluscivore shorebirds. Diet
composition was not associated with the length of the bill, but with the
mass of the muscular gizzard. Gizzard mass, which unlike bill length is a
phenotypically flexible trait, enables great knots to adjust to changing
food resources as an individual, i.e. instantly responding to the food on
offer. For migratory species like great knots which rely on seasonal
sequences of inter distant feeding areas offering prey with a variety of
characteristics, the capacity to individually adjust appears a key
adaptation.