Molluscivorous red knots rapidly adjust to a plant diet

Dietary flexibility is key to adjusting to environmental change. In
Mauritania, the seemingly obligatory molluscivorous red knots Calidris
canutus canutus were observed to eat seagrass rhizomes. To study the
ability of knots to live on plant material, we performed a diet-change
experiment on captive individuals. Two groups of five were fed
protein-rich pellets for 13 weeks, then plant-based pellets for 6 weeks,
then reversed back to protein-rich pellets for 4.5 weeks. During the first
days following the shift to the plant diet, body mass declined with 14%
before increasing and stabilizing to lower levels. Faecal colour changed
from green (i.e., gall, suggesting starvation) to brown and was produced
in larger quantities when the birds ate plant pellets. These experimental
data prove that knots can indeed live on a plant-based diet, the observed
changes suggesting that adjustments of the digestive system, i.e., gut
morphology and microbiome, take only a few days.