Feathered parents face gaping mouths and sudden weight loss
Photo: Karen Schik
Nest building is done, eggs were laid and hatched and now the young need to be fed, and fed, and fed. With day-length in the 15-hour range, bird parents are on the go almost constantly to provide their growing chicks with enough energy for quickly developing tissues. For many of the neotropical migrants, the parent brings food, composed often of several insects, to the nest and inserts them into the gaping mouth of the young. A parent can make over 50 feeding trips in a day, depending on the brood size. Rarely does serendipity enter the equation when nature is at work; songbirds hatch just as there's a corresponding increase in the availability of flying insects demanded by the young birds.
Studies have shown that adults rearing young experience weight reduction of up to 20%. This weight reduction might be a result of the additional energy expended making all of those food-gathering trips; after all, it is more difficult to find the time to feed yourself when you have five ever-gaping mouths to fill. However, there is some evidence that this weight reduction might be intentional and actually result in more successful breeding. By reducing weight, the birds might benefit from a savings associated with flying all those extra flights because this form of locomotion requires a lot of energy. By being lighter, flying requires less energy; it's the old wing-loading hypothesis (Norberg. Cavitt & Thompson).
When you are lying in bed this month, awaken by the birds singing loudly at 4:30 a.m., have some respect. Keep in mind that they have no time to dawdle as their young demand to be fed so they themselves can grow and fledge and prepare themselves for the arduous migration journey south coming up in just a short number of weeks.
If you need a quick pick-me-up, here's a great Youtube video of yellow warblers feeding their babies: