Nestlings appear to put a lot of effort into begging. Stretching their scrawny necks and gaping wide, chicks seem to invest a significant amount of energy to attract the next beak full from their parents. So, how much does begging cost nestlings? David Martín-Gálvez and his Spanish colleagues, from the Estación Experimental of Zonas Áridas in Almería and the University of Granada, explain that enthusiastic begging could be costly so the team decided to estimate the cost of exaggerated begging relative to the benefits of being well fed by their parents. Giving newly hatched magpie chicks an appetite stimulant (cyproheptadine) in the hope that it would make the youngsters feel hungry and beg harder, the team monitored the chicks to see what affect it had on their behaviour ().
‘Cyproheptadine is broadly used in humans, including children, as a safe and effective appetite stimulant,’ explains Martín-Gálvez.
Having identified new magpie nests in the surrounding countryside, the team gave magpie youngsters a tiny dose of cyproheptadine every 2 days during their development in the nest, and filmed the 10–12 day old birds as their parent's returned from foraging. They saw that the chicks that had been treated with cyproheptadine begged more often, but with the same intensity as chicks that had received a drink of water instead of the stimulant. So, the cyproheptadine-treated chicks seemed to be hungrier than the chicks that had only had a drink, but how did the parents react to the chicks' demanding behaviour?
Placing collars around the chicks' necks for 2 h so that the nestlings couldn't swallow food, the team were able to measure how much each chick had been fed while monitoring their mass. They found that the chicks that begged more often received 209% more food than the normal chicks, and the youngsters also lost more mass during the brief period when they couldn't swallow. So the chicks that begged more often had attracted more of their parents' attention; however, they had also used more energy.
But what was the long-term effect of the chicks' increased begging behaviour? Monitoring the chicks until they were about to fledge, the team measured the chicks' growth and the strength of their immune systems to find out whether additional begging had given them a better start in life. It had. Not only were the high-frequency beggars heavier and larger but also they had a stronger immune response than chicks that begged at the normal rate. Despite the additional energetic cost of begging, the hungry chicks had benefitted from the increased parental attention that they attracted.
So why don't begging chicks bend the rules and cheat to attract more than their fair share from mum and dad? Martín-Gálvez and his colleagues explain that there could be several reasons. Greedy chicks that beg dishonestly could go on to produce even greedier young, escalating to the point where the parents and their chicks could not survive the chicks' excessive demands, removing the tendency to cheat from the gene pool. Alternatively, the chicks and their parents could pay some other way – as yet unidentified – for rearing deceitful offspring and the team is keen to find out which indirect costs keep cheating chicks in check.
