These demanding little nestlings are growing fast. According to the Cornell Lab of Ornithology, catbirds that hatched at 3 grams should now be over 20 grams, and supporting this growth spurt clearly requires a lot of effort from the parents!
Interestingly, studies on songbirds like Great Tits and Purple martins seem to show a cap on energy expenditure, even when these birds are clearly working hard. So what’s going on? Some of the coolest work I’ve seen of this actually comes from seabirds. Using some nifty techniques to measure both total daily energy expenditure and resting metabolic rate (RMR, i.e. self-care energy), researchers compared breeding and non-breeding Black-legged Kittiwakes. They found that breeding birds had higher energy expenditure but actually lowered their estimated RMR (Welker et al. 2014). So while there may be a cap on energy expenditure, these birds may instead allocate more of that energy to the chicks than to themselves.
In other words, breeding birds were reducing their self-care in order to put more energy toward raising the chicks! (Human parents reading this: “duh.”)
With that in mind, it makes sense that parents would sneak a quick snack whenever they can. You’ve probably seen this in the previous videos…Any guesses?