Listen for a high-pitched, faint, wheezy whistles and you might find you’re surrounded by a flock of Cedar Waxwings searching for berries in the trees above you.
These birds are dedicated fruit lovers — any bite-sized fruits, any season. But they also feast on aerial insects when they are abundant, sallying out from a tree perch to grab an insect, and returning to the same perch.
Cedar Waxwings can survive on a diet of just fruit for several months at a time, without protein supplement (fruits are notoriously low in amino acid content, as well as total calories). How do they manage???
Most frugivores, like Cedar Waxwings and Robins, eat a large variety of fruits that are highly variable in their nutrient constituents in order to obtain what they need in their diet. Some fruits are very high in sugar content; some are higher in lipids. Waxwings are sugar specialists, while Robins are lipid specialists, and their particular preferences provide them with the most highly absorbable diet.
In fact, Cedar Waxwings have an exceptionally good absorptive capacity for sugars, not only in their small intestine, but in the proximal part of their colon as well (an unusual place to transport sugar). It is thought that the accelerated sugar transport capacity of their intestine actually enhances amino acid transport as well, because these birds can actually remain in positive nitrogen balance on fruit diets that other frugivores (like robins) cannot.
The best way to maximize both your caloric and essential nutrient intake is to process food quickly. Most frugivores manage to separate fruit pulp from seeds very quickly in their intestine, and purge the gut of the indigestible seeds while retaining the pulp to extract every vital nutrient. In fact, the seeds of an ingested meal of berries might appear just 20-30 min after Cedar Waxwings have eaten. That’s why you shouldn’t stand under a tree where frugivores are feeding.