Diets of Wedge-tailed Eagles 'Aquila audax' and Little Eagles 'Hieraaetus morphnoides' breeding near Canberra, 2008-2009

Abstract

In the Australian Capital Territory during 2008-09, the diet of breeding Wedge-tailed Eagles 'Aquila audax' consisted of 65 per cent mammals, 33 per cent birds and 1 per cent reptiles by number ('n' = 94 prey items from 10 nests), of which 19 per cent consisted of macropods, 34 per cent rabbits (mostly adults, plus 4% hares), and a range of other large mammals, many probably eaten as carrion. Breeding Little Eagles 'Hieraaetus morphnoides' took 52 per cent mammals, 45 per cent birds and 3 per cent reptiles by number ('n' = 58 prey items from six nests), of which 2 per cent consisted of macropod (one small joey kangaroo) and 50 per cent rabbits (mostly juveniles). Both eagle species took more rabbits in 2008-2009, compared with two earlier periods in 2002-2003 and 2004-2007. By biomass Wedge-tailed Eagles took 93 per cent mammals (20% rabbits, 45% macropods); Little Eagles took 73 per cent mammals (almost entirely rabbits) and 24 per cent birds. Geometric Mean Prey Weight for Wedge-tailed Eagle prey was 1650 grams, for Little Eagles 337 grams. Standardised food niche breadth was 0.205 for Wedge-tailed Eagles, and narrower (0.143) for Little Eagles. The Shannon Index for Wedge-tailed Eagles was 2.75, for Little Eagles 2.28. Although a Pianka Index suggests 46 per cent overlap in prey used by the two eagles, the great difference in GMPW and heavy use of rabbits by Little Eagles suggest that there is little interspecific competition for prey. Little Eagles may be declining in the ACT because rabbits, their main prey, are poisoned, and this poisoning may affect Little Eagles more than some other raptors.