Have you ever wondered if you deserve your food? For bird species that provide parental care, foraging and bringing back food is a tricky balance between nurturing progeny and conserving energy. The situation becomes bleak for offspring when resources become scarce; if it doesn’t look like the chicks will survive, parents may decide to abandon them and try again next breeding season.
How do the offspring tip the balance in their favor? They beg. Adult birds adjust their food provisioning accordingly. Whether begging behavior indicates hunger or quality, however, has been the subject of much debate. The need hypothesis states that chicks call more frequently if they are hungrier. The quality hypothesis states chicks will call more to display their good health, showing parents they are worth the investment. There are studies that offer support for both of these hypotheses.
Rector et al., 2014 studied the Atlantic Puffin to understand why offspring beg, and to determine which model (need or quality) was more consistent. Puffins were chosen because they only produce one offspring per breeding season, eliminating other factors such as sibling competition. Puffin chicks produce two types of calls when they beg; a “peep” and a “screech”.
The study tested puffins in their natural environment using two treatments; after an initial period of observation, some chicks were given extra food to supplement what their parents brought, while others were left as controls. The team recorded the type of food, if any, parents brought back during each nest visit and whether chicks peeped or screeched. For each chick, they also monitored the body mass divided by the length of the tarsus (the leg bone) as a measure of body condition.
The researchers noticed that chicks in poor body condition produced more screeches than did chicks in good body condition. When given additional food, chicks in good condition increased their peep rates more than did chicks in poor condition. This seemed to suggest that puffin chicks give two distinct signals; frequent screeching to signal need, or frequent peeping to signal quality.
So, the study offers support for both the need and the quality hypotheses. Chicks may use either call to convey different information about their nutritional needs and their health. When food becomes more elusive, chicks can shift their strategy and advocate for themselves by advertising their quality.
Given these results, it’s interesting to think about whether chicks can use this to their advantage and send dishonest signals. Because Atlantic Puffins live in burrows, parents can’t really see their offspring. Thus, offspring could potentially exaggerate their quality and acquire more food.
Finally, this study offers insight into the complexity of parent-offspring interactions. Conflicting interests arise depending on environmental factors, particularly food scarcity. Do the parents save their energy for another breeding season, or should they invest in a chick that might not make it? As capelins are the main constituent of the Atlantic Puffin’s diet, overfishing has serious consequences for their survival as a species. It just goes to show, puffins have to make tough decisions, too.
Rector M. E. et al, 2014. Signals of need and quality: Atlantic puffin chicks can beg and boast. Behavioral Ecology 25(3), 496–503