Non-breeding Diet of the Barking Owl near Armidale, New South Wales

The breeding and non-breeding diets of a family of Barking Owls Ninox connivens near Armidale, on the Northern Tablelands of New South Wales, have been described previously by Debus (1997) and Debus et al. (1998). These data for the non-breeding season, collected in April1996 and 1997, comprised a small sample of 10 items of prey from four pellets, pellet debris and food remains (Debus 1997). This note reports a further 22 prey items, from 13 intact pellets and fragments from a further six (total estimate 19 pellets), collected from the same pair of Owls on Boorolong Creek by RBS between March and early June 1998. The site, methods of analysis and sources of prey weights were as previously reported (Debus et al. 1998).

The 13 intact pellets from the adult Owls' non-breeding season in 1998 averaged 39 x 24 mm (23-51x 18-31 mm). This sample of pellets and debris contained the remains of native arboreal mammals (14% by number, 68% by biomass), birds (9% bv number. 29% bv biomass). and insects, mainlv ortho terans and beetles

DEBUS, SHEPHERD & ROSE: 44 Non-breeding Diet of Barking Owl

AUSTRALIAN BIRD WATCHER

Table 1

Non-breeding diet of a pair of Barking Owls at Boorolong Creek, Armidale, N.S.W., March-June 1998: minimum number (n) of prey individuals in pellets and debris

(13 pellets and fragments from a further six pellets).

Species

Sugar Glider Petaums breviceps

Red-rumped Parrot Psephotus haematonotus Olive-backed Oriole Oriolus sagittatus Total birds

Orthopterans Scarab beetle Repsimus aeneus Other scarabs (Scarabaeidae) Water beetle (Hydrophilidae) Mantis (MantJdae) MothAbantiades magnificus (Hepialidae) Total insects

Total

(77% by number, 3% by biomass; Table 1 ).

Estimated body weight n (g)

128

65 100

1 1 1 1 1 1

3

1 1 2

8 1 5 1 1 1

17

22

%

14

9

77

100

This sample contained a greater proportion of mammals, fewer birds and many more insects by number, and a substantially greater biomass contribution by mammals than by birds, compared with the previous, limited autumn sample reported by Debus (1997). This difference may have resulted from the larger sample size collected in 1998, spanning a greater period and including the warm month of March when insects, and particularly orthopterans, are still readily available as food.

Overall, from samples spanning all seasons, it appears that the diet of this pair of Barking Owls is, by biomass, dominated by mammals in autumn and early winter, birds in late winter, and about equally by birds and mammals in the breeding season (Debus 1997, Debus et al. 1998). Insects, although numerically dominant in the pair's diet in all but the coldest months, always contributed <5% by biomass: only slightly more in the warmer post-breeding months than during the breeding season, with more orthopterans taken in autumn than at other times. This result suggests that, throughout the year, adult breeding pairs of Barking Owls in temperate climates are dependent on vertebrates for most of their food biomass. It also supports the suggestion by Kavanagh et al. (1995) that Barking Owls that feed mostly on invertebrates in autumn are probably dispersing immatures subsisting in suboptimal habitats. Further generalisations on Barking Owl diets will be possible after more comprehensive, quantitative data are gathered from a range of locations, covering all seasons, and by comparing the diets of breeding pairs and non-breeding individuals.

We thank John Peter and Dr Graham Cam for reviewing a draft.

References

Debus, S.J.S. (1997), 'The Barking Owl in New South Wales',Aust. Birds 30, 53-80. --, Shepherd, R.B. & Rose, A.B. (1998), 'Diet of the Barking Owl Ninox connivens near

Armidale, New South Wales',Aust. Bird Watcher 17, 302-305.

VOL.18 (1) MARCH 1999 EMMERSON: Female Button-quail Tending Chicks 45

Kavanagh, R.P., Debus, S.J.S., Rose, A.B. & Turner, RJ. (1995), 'Diet and habitat ofthe Barking Owl Ninox connivens in New South Wales', Aust. Bird Watcher 16, 137-144.

By S.J.S. DEBUSt, R.B. SHEPHERD2 and A.B. ROSE3

1Division of Zoology, University of New England, Armidale, N.S. W 2351 226 Kentucky Street, Armidale, N.S. W 2350 3Associate, The Australian Museum, 6-8 College Street, Sydney, N.S. W 2000

· (present address: 61 Boundary Street, Forster, N.S. W 2428)

Received 13 July 1998 •