Suchergebnisse

The abundance of Australian fur seal pups was determined at Seal Rocks,
Westernport, Victoria in late December 1997 using a mark–recapture
procedure with repeated recapture sessions. Pups (n
= 1291) were marked by clipping the black guard hair on the head to
reveal lighter underfur. Recaptures from the whole colony were made on eight
occasions 1–3 days later. In the recapture sessions, a mean of
32% of sighted pups had been marked. Estimates of pup numbers over the
eight recapture sessions were calculated using the Petersen estimate and then
combined by taking their arithmetic mean. The combined estimate was 4024
(95% confidence range 3908–4141). In 1991–92, a similar
procedure led to an estimate of pup numbers of 2817 (95% confidence
range 2703–2930). For both breeding seasons, estimates of pup numbers
from each recapture session were also combined assuming a joint hypergeometric
distribution; there was little difference in the results from the two
procedures, although the confidence intervals for the hypergeometric mean were
smaller than those for the arithmetic mean.
From 1991–92 to 1997–98, pup numbers increased by 43%, at
an exponential rate of 0.059 (95% confidence range
0.0526–0.0664), equivalent to 6.1% per annum
(5.4–6.9%). This is greater than the rate of increase of pups at
the colony between 1968–69 and 1991–92, which was 0.023
(95% confidence range 0.0198–0.0268), equivalent to 2.4%
per annum (2.0–2.7%).
Because of the rapid rate of increase of the Australian fur seal colony at
Seal Rocks and the importance of the locality for tourism, we recommend that
the abundance of pups there be determined every 3–5 years using a
mark–recapture technique.

Tree planting has become a cornerstone strategy for natural resource management in agricultural landscapes, yet its contribution as habitat for woodland birds has not been fully investigated. A case study from the Holbrook region in southern New South Wales was used to assess woodland birds in young plantings of native trees and shrubs. Ground-foraging insectivorous woodland birds were under-represented in the plantings, partly due to a lack of native forb diversity (wildflowers) and leaf litter. Of 69 woodland bird species recorded over a three-year period, 48 species (70%) occurred in planted sites, 59 species (86%) occurred in remnant woodland, and 34 species (49%) occurred in adjacent paddock sites. The greater diversity of birds in planted sites relative to paddock sites was mostly due to understorey birds. The proportion of mist-netted birds recaptured was similar in both planted (15%) and remnant woodland (16%) sites, suggesting that individual birds were staying in planted sites. The proportion of woodland birds showing breeding activity (as measured by the presence of a brood patch) was slightly lower in planted sites (24% of all woodland species) than in remnant woodland (29%). Birds such as the superb fairy-wren, red-browed finch and southern whiteface were more likely to occur in planted sites, suggesting that plantings provide unique, transitional-stage habitat within agricultural landscapes. Restoring native forbs, as part of a broader strategy of woodland management, will help to reverse the decline of ground-foraging insectivorous woodland birds in agricultural landscapes.