Ten Seabird species Issues paper

Department of the Environment and Heritage, May 2005
ISBN 0 6425 5005 0

Part B: Conservation Issues For Specific Species/Groups (continued)

3. Heard Shag and Macquarie Shag - Conservation issues

Heard Shag Phalacrocorax nivalis
Conservation Status Endemic Species
BirdLife International Status Least Concern
EPBC Status Vulnerable
 
Macquarie Shag Phalacrocorax purpurascens
Conservation Status Endemic Species
BirdLife International Status Least Concern
EPBC Status Vulnerable

3.1 General Introduction

Cormorants and shags are distinctive aquatic birds typically breeding on both mainland and island sites. Those that are restricted to remote islands are typically sedentary. Recent reviews of the taxonomy have resulted in the recognition at the specific level of several forms restricted to particular islands (Shirihai 2002). The Heard and Macquarie Shags represent such forms and both have been the subject of several studies (eg Brothers 1985, Green 1997a,b; Green and Williams 1997).

3.2 Taxonomy

Both endemic species.

The taxonomy of the blue-eyed (imperial) shag complex remains confused. Some authors recognised eight subspecies of Phalacrocorax atriceps (e.g. Harrison 1983) whilst others (e.g. Marchant and Higgins 1990) recognise eight distinct species, with P. nivalis and P. purpurascens restricted to Heard and Macquarie Islands, respectively. Others considered the Imperial Shag (P. atriceps) group to comprise multiple subspecies, including both Heard and Macquarie birds (Turbott 1990, BirdLife International (2004). Such a treatment consequently results in the Least Concern rating by BirdLife International (2004).

3.3 Distribution

Heard Shags are restricted to breeding in approximately four colonies at Heard Island. There are no breeding records or observations from the McDonald Islands (Johnstone 1982, Vining 1983). On Macquarie Island, there are 23 recorded breeding sites for Macquarie Shags, with all but two sites restricted to offshore stacks or islets, or stacks attached to the shore (Brothers 1985). Not all sites are used each year, and birds may interchange between colonies. Macquarie Shags have also been recorded nesting at adjacent Bishop and Clerk Islets, 37 km south of Macquarie Island (Lugg et al. 1978, N. Brothers pers comm.).

Heard and Macquarie Shags are sedentary, making only local movements around their respective islands. Brothers (1985) reported that they are poor fliers, unable to make headway in strong winds (> 40 knots), and their morphology (small wings, heavy bones and water permeable plumage) restricted long range movements. Macquarie Shags are restricted to inshore waters during the breeding season, but may travel further offshore, up to 100km, during the winter season.

3.4 Population Size and Trend

Until recently, the total breeding population of Heard Shags was estimated to be between 100 and 200 pairs known from three colonies at Sydney Cove, Saddle Point and Stephenson Lagoon (Green 1997b). Roosting sites are more widespread and numerous (Pemberton and Gales 1987). In November 2001, a large colony of approximately 850 pairs on three terraces adjacent to a large macaroni penguin Eudyptes chrysolophus colony at Cape Pillar was discovered. The total breeding population is estimated at approximately 1100 pairs for the 2000/01 summer (Woehler in press).

The number of Macquarie Shags breeding on the island in the 1970s was estimated by Brothers (1985) at 660 breeding pairs, an estimate that does not include the nests recorded from Bishop and Clerk Islets, where Lugg et al. (1978) estimated 100 pairs. More recently,164 nests in three colonies were observed by Brothers (unpublished data).

A 2003 survey on Macquarie Island comprised an island wide search of all known and potential breeding sites. Eleven colonies comprising 472 nesting pairs were located in October 2003, although it is difficult to detect trends from these data, this figure represents 30 % fewer than the 660 pairs observed in 19 sites in the 1970s (M. Schulz and J. Lynn unpublished data).

Absence of comparable longitudinal data preclude assessment of population trends for either species of shag. Further systematic surveys are required to confidently assess trends.

3.5 Breeding Biology, Ecology and Diet

These are sedentary species that breed in colonies and are gregarious at roost sites and when feeding. Nests typically comprise a truncated column structure composed of mud, guano and vegetation. A clutch of 1 to 3 blue-green eggs being laid in October-November, although eggs have been observed in late September on Macquarie Island (Brothers 1985). On Macquarie Island most chicks hatch by late December, and are independent of adults by mid-February (Brothers 1985). The timing of egg laying for Heard Shags can vary widely, with the earliest eggs being laid from mid September, this lability in breeding season being interpreted as an adaptation to exploit periods of high food availability (Green 1997b).

Breeding success is problematic to assess given the habit of the young birds moving from their nests before becoming fully independent of parents. During three seasons on Macquarie Island, Brothers (1985) estimated mean success rates of 57-61%, reflecting a production rate of 1.0 to 1.9 chicks per nest. A similar breeding success rate of 59% has been observed for Heard Shags, where nests produced an average of 1.9 chicks per nest (Green 1997b).

During the breeding season, adult Macquarie Shags forage for only 2-4 hours at a time, feeding their chicks ca 6 times per day (Brothers 1985). The Macquarie Shags diet consists almost entirely of two species of benthic fish, whereas the Heard Shag feeds mainly on polychaete worms and fish. At Heard Island, the shags fed exclusively on polychaete worms during the non breeding season, but switched to a diet of notothenid fish when feeding chicks (Green and Williams 1997). Compared with other shag species, Heard Shags appear to perform shorter and shallower dives, suggesting that adequate food is available in shallow waters around the island.

There are no data on adult or juvenile survival rates for either species, the mobility of birds among colonies making such assessments difficult. Brothers (1985) reported that banding records showed that Macquarie Shags can live for at least 13 years.

3.6 Threats specific to the Herald Shag and Macquarie Shag

Both Heard and Macquarie Shags are considered threatened because the populations are small and restricted in distribution. As a result, the birds could be adversely affected by effects of climate changes on sea temperature and food supply (Garnett & Crowley 2000) in addition to other threats that affect small and vulnerable species of seabirds (see Part A).

Heard Island is predator free, so that the threat that may be posed by feral pests remains absent on this island. In contrast, cats were identified as a possible predator of Macquarie Shag chicks, with cats being regularly observed on the periphery of colonies (Selkirk et al. 1990). Cats have since been eradicated from Macquarie Island, but rats have been observed in disused nest bowls on Macquarie Island (M, Schulz and J. Lynn unpublished data).

The two major causes of mortality of Macquarie Shag nestlings were predations by skuas, Catharacta lonnbergi, and starvation (Brothers 1985). Severe weather conditions likely contribute more than any other factor to mortality in both species, with fluctuations in breeding success being attributed to frequently inclement weather for Heard Shags (Pemberton and Gales 1987). The effects of adverse weather on breeding success may be manifested not only be physical destruction of nests but also by restricting access to available prey. On Macquarie Island up to 90% mortality of shag nestlings has been observed after a single storm (N. Brothers pers comm. in Pemberton and Gales 1987). Storms on Macquarie Island have also been directly implicated in the death of adults when colonies are wave-washed and in severe winter storm events (M. Schulz and J. Lynn unpublished data).

Human mediated deaths have also been recorded for both species, with fatal strikes with radio masts being recorded for both locations (Brothers 1985, Green 1997), although fewer mortalities are generally reported at Heard Island. The shallow and inshore foraging behaviour of the shags makes them unlikely candidates for interactions with commercial fishing operations around Heard and Macquarie Islands. A total prohibition on commercial fishing within 13 nautical miles of Heard Island likely minimises against potential interactions with the shags. Fishing is also prohibited within 3 nautical miles of Macquarie Island, and the only recorded interaction of a Macquarie Shag interacting with fishing vessels relates to an occasion on a trawler targeting toothfish Dissotichus spp. in 2002 when a bird 'landed on the bow of a boat, and flew off leaving a few drops on blood' (AFMA unpublished data).

3.7 Issues and Recommendations

  • On Macquarie Island, conduct annual island-wide breeding census, incorporating visits to all sites known to have been used for breeding. Surveys to be timed and recorded so that meaningful assessments of population status and inter-annual variation can be drawn.
  • The presence/status of the Macquarie Island shag population breeding on Bishop and Clerk Is should be assessed.
  • Complete surveys of Heard Shag populations to be undertaken when possible in order to assess population status.
  • Progress feral pest eradication program on Macquarie Island to mitigate possibility of rat predation on eggs and chicks.
  • Ensure effective quarantine programs at all breeding sites to minimise introduction of pests.
  • Where possible long radio and HF dipole aerials should be replaced by whip aerials to reduce the incidental morality caused by bird strike.
  • All colonies to be protected and managed in such a way that human disturbance is minimised.
  • Maintain current prohibitions of fishing in waters immediately adjacent to the breeding islands.

3.8 References

BirdLife International. (2004) Threatened birds of the world 2004. CD-ROM. Cambridge, U.K: BirdLife International.

Brothers, N. P. (1985) Breeding biology, diet and morphometrics of the King Shag, Phalacrocorax albiventer purpurascens, at Macquarie Island. Australian Wildlife Research 12: 81-94.

Garnett, S.T. & Crowley, G.M. (2000) The Action Plan for Australian Birds. Environment Australia: Canberra.

Green, K. (1997a) Biology of the Heard Island Shag Phalacrocorax nivalis. 1. Breeding behaviour. Emu 97: 60-66.

Green, K. (1997b) Biology of the Heard Island Shag Phalacrocorax nivalis. 2. Breeding. Emu 97: 67-75.

Green, K. and Williams, R. (1997) Biology of the Heard Island Shag Phalacrocorax nivalis. 3. Foraging, Diet and Diving Behaviour. Emu 97: 76-83.

Harrison, P. (1983) Seabirds: An identification guide. Sydney: Reed

Johnstone, G.W. (1982). Zoology. Pp. 33-39 in Expedition to the Australian Territory of Heard and McDonald Islands 1980. Eds C. Veenstra and J. Manning. Division of National Mapping, Technical Report 31, Canberra.

Lugg, D.J., Johnstone, G.W., and Griffin, B.J. (1978). The outlying islands of Macquarie Island. Geogr. J. 144: 277-87.

Marchant, S. and Higgins, P.J. (eds). (1990) The Handbook of Australian, New Zealand and Antarctic Birds. Volume 1. Oxford University Press, Melbourne.

Pemberton, D. and Gales, R. (1987) Notes on the status and breeding of the Imperial Cormorant, Phalacrocorax atriceps at Heard Island. Cormorant 15: 33-40.

Selkirk, P.M., Seppelt, R.D., and D.R. Selkirk (1990) Subantarctic Macquarie Island: environment and biology. Cambridge University Press, Cambridge.

Shirihai, H. (2002) The complete guide to Antarctic wildlife. Princeton University Press, Princeton.

Turbott, E. G. (Convenor) (1990) Checklist of the birds of New Zealand and the Ross Dependency, Antarctica. 3rd Edition. Random Century, Auckland.

Vining, R. (1983). Heard Island 1983 Scientific Reports. Garvan Institute of Medical Research, Sydney

Woehler, E.J. (in press) Status and conservation of the seabirds of Heard Island. In Green K & Woehler EJ (eds) Heard Island: Southern Ocean Sentinel. Surrey Beatty, Sydney.

Table 3.9: Summary of biological information for Heard Shag and Macquarie Shag
 
Heard Shag
Refs
Macquarie Shag
Refs
Common name Heard Shag
 
Macquarie Shag
 
Scientific name Phalacrocorax nivalis
 
Phalacrocorax purpurascens
 
Conservation status
-Australia EPBC
-BirdLife Int.

Vulnerable
Least Concern (see text)


G

Vulnerable
Least Concern (see text)


G
Australian breeding localities Heard Island
A
Macquarie Island, Bishop and Clerk Islets.
A, D
Extra-limital breeding localities None
A
None
A
Foraging localities Local waters around Heard Island
B
Local waters around Macquarie Island and Bishop & Clerk Islets.
C
Annual breeding pairs
- Aust populations
- Global

1100
as above (endemic species)
E
About 700
as above (endemic species)
B
Australian % of global population 100%
 
100%
 
Breeding frequency
(annual/biennial)
Probably annual
 
Probably annual
 
Clutch size 1-3
F
1-3
B
Breeding success
- % chicks fledged from eggs laid
Variable, ca 59% in one season
F
Variable, ca 57-61% mean for three seasons
A, B
Age at first breeding No data
 
2 years, but most breed at 4 years or later
B
Juvenile survival No data
 
No data
 
Adult survival No data
 
No data, birds can live for at least 13 years
B
Nest site Surface nesting. Truncated cone nests composed of mud, guano and vegetation
G
Surface nesting. Truncated cone nests composed of mud, guano and vegetation
B
Nesting behaviour Colonial
A
Colonial
A
Breeding season Typically Sep -Feb
F
Typically Oct-Feb
B
Food / Foraging Shallow-inshore waters, targeting polychaete worms and notothenid fish
C
Inshore waters, targeting benthic fish
B
Refs: A - Marchant and Higgins 1990; B - Brothers 1985; C - Green and Williams 1997; D - DPIWE unpublished data; E - Woehler in press; F - Green 1997; G - BirdLife International 2004.