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 relat ionships under contrasting population densities during three successive yea rs, centred on a crash year (1992). Poor diet quality and high neonatal mor tality characterised the pre-crash year (1991). During the crash year, neon atal mortality was high at the onset of the lambing season, but young survi val increased rapidly when environmental conditions improved. Diet quality was high and neonatal mortality was reduced in 1993 (post-crash). Total suc kling duration was constant between years, but the higher frequency of unsu ccessful suckling attempts and allosuckling attempts in 1991 suggested a li mitation of maternal expenditure for that year. Lambs grazed earlier, playe d 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 f emales' condition and constrain maternal expenditure. However, maternal exp enditure increased as soon as diet quality improved, suggesting that female s adjusted maternal care by tracking environmental conditions. (C) 1999 Els evier Science B.V. All rights reserved.