Nursing behaviour and mother-lamb relationships in mouflon under fluctuating population densities.

The mouflon population of the subantarctic Kerguelen archipelago undergoes periodic die-offs and shows marked interannual variations in density. This situation allowed us to investigate nursing behaviour and mother-lamb relationships under contrasting population densities during three successive years, centred on a crash year (1992). Poor diet quality and high neonatal mortality characterised the pre-crash year (1991). During the crash year, neonatal mortality was high at the onset of the lambing season, but young survival increased rapidly when environmental conditions improved. Diet quality was high and neonatal mortality was reduced in 1993 (post-crash). Total suckling duration was constant between years, but the higher frequency of unsuccessful suckling attempts and allosuckling attempts in 1991 suggested a limitation of maternal expenditure for that year. Lambs grazed earlier, played less, spent less time resting and had lower growth rates in 1991 than in other years. These results suggest a greater mother-offspring conflict when food resources were limited. Adverse environmental conditions may affect females' condition and constrain maternal expenditure. However, maternal expenditure increased as soon as diet quality improved, suggesting that females adjusted maternal care by tracking environmental conditions.