Among the many amazing traits of the birds I currently study is their remarkably rapid development as nestlings. When the chicks hatch from their eggs after a two-week incubation period, they look like tiny pink monsters, capable of little and requiring constant food and looking after. (In other words, not unlike human babies.)
Less than three weeks later, the fledglings leave their nest; seeing the world outside of their nesting cavity and flying for the first time in their lives (somewhat unlike human babies, to the best of my knowledge). The transformation isn’t far off that of a caterpillar to a butterfly.
To see how and how rapidly the young birds change, I visited a pied flycatcher (Ficedula hypoleuca) nest and took pictures of one of the chicks every day until it fledged. A €2 coin (approx. 2.5cm/1″ diameter) was included in the pictures for scale, to better show the extent to which the nestlings grow.
Normally, we only visit the nests when the eggs are expected to hatch, and again a few days before the chicks fledge and leave their nests. Although the difference in the chicks between these visits is obvious, it hardly stands out when monitoring dozens of nests simultaneously — especially as one typically ends up losing any concept of time over the course of the field season anyway. Seeing the very notable changes after just 24 hours each time was quite astounding. Even after going back and forth through the photo series several times, and indeed having seen it happen in the first place, it remains hard to believe how this strange pink shape with black tufts of fluff becomes a complete bird so rapidly.
So, what fuels this rapid growth? As it happens, that is one of the main questions I am looking to answer in my current research. Watch this space!