Experimental evidence for offspring learning in parent-offspring communication

The offspring of birds and mammals solicit food from their parents by a com bination of movements and vocalizations that have come to be known collecti vely as 'begging'. Recently, begging has most often been viewed as an hones t signal of offspring need. Yet, if offspring learn to adjust their begging efforts to the level that rewards them most, begging intensities may also reflect offsprings' past experience rather than their precise current needs . Here we show that bird nestlings with equal levels of need can learn to b eg at remarkably different levels. These experiments with hand-raised house sparrows (Passer domesticus) indicated that chicks learn to modify begging levels within a few hours. Moreover, we found that the begging postures of hungry chicks in natural nests are correlated with the average postures th at had previously yielded them parental feedings. Such learning challenges parental ability to assess offspring needs and may require that, in respons e, parents somehow filter out learned differences in offspring signals.