Effect of food shortage on the physiology and competitive abilities of sand martin (Riparia riparia) nestlings

We examined developmental and behavioural plasticity of sand martin (Ripari a riparia) nestlings hand-reared under laboratory conditions. We created si x broods of six 4-day-old nestlings and randomly assigned them to one of th e two following feeding regimens, each lasting for 3 days: (1) all nestmate s fed a similar, limited amount of food (FR nestlings). This simulated sync hronous hatching under conditions of food restriction. (2) Half the brood w ere food-restricted (FR/AL nestlings), and half were fed ad libitum (AL nes tlings), as in asynchronously hatched broods with differential food allocat ion. Under both regimens, food restriction resulted in a reduction in body mass, intestinal mass, pectoral muscle mass, fat reserves, body temperature and resting metabolic rate (RMR). However, it simultaneously triggered a s ignificant increase in intestinal uptake rates of L-proline and locomotor a ctivity, quantified as frequency of crawling into the artificial nest tunne l by individual nestlings. Locomotor activity and intestinal uptake rates O f L-proline by FR nestlings were higher than those of FR/AL young, while bo dy temperature and RMR of FR nestlings were lower. We conclude that food-restricted nestlings responded actively to food short ages by upregulating their gut function, reducing the energy costs of maint enance and increasing locomotor activity. These behavioural and physiologic al responses were strongest in broods of similar-sized FR nestlings, which can be interpreted as an escalation of sibling competition. Thus, developme ntal and behavioural plasticity may be an important factor in the evolution of sibling rivalry.