Zebra finch nestlings beg more under better nutritional conditions

Providing parental care involves costs for the parents when investing resources such as food and time to raise their offspring. In many species, offspring communicate their need by begging signals which often are linked to their physiological condition but also may be affected by the expectation they may develop depending on previous parental behaviour. To test whether or not offspring begging is affected by the food quality to which parents have access, we experimentally manipulated the early nutritional conditions of zebra finch (Taeniopygia guttata) nestlings by providing the parents with either a low or a high quality diet. We expected that lower early nutritional conditions increase begging behaviour resulting from a presumed higher nestling need. Yet, the experiments revealed that broods of nestlings begged more intensely when they were raised on a high compared to a low quality diet. Nestlings raised under high quality food conditions may have a higher begging intensity due to their higher need associated with a fast growth trajectory. Likewise, lower begging intensity by nestlings raised on low quality food might result from a general delay in development, or nestlings adjusted their begging to behavioural adjustments made by parents as a response to the different diets. These findings highlight that begging signals can be affected by a complex set of factors and expands the classical view of signalling need. Begging call rates can increase with offspring condition and with their expectations about the quality of food that can be provided by the parents.