Surveillance Vol.15 No.2 1988
Where have all the penguins gone?
In 1984 the Wildlge Service (now
Department of Conservation) began
studying the rockhopper penguin
(Eudyptes chrysocome) at Campbell
Island. These studies were initiated in
response to a series of reports which
indicated that during the last 40 years'
there had been a large decline in the
number of rockhopper penguins.
Examination of photographs taken
between 1942 and 1945 revealed that
during this period the breeding population exceeded one million birds.
Investigations since 1984 have shown
that the rockhopper penguin breeding
Fig. 1: Where have all the penguins gone?
population now numbers only 1 10 000
birds. Field trials in 1984 showed that
predation of eggs by Norway rats was
not a cause in the decline in bird numbers. Neither could the decline in
numbers be attributed to feral cats or
disturbance of penguin nest sites by
humans or feral sheep.
Other possible causes of the decline
in penguin numbers included a change
in food supply and disease. Investigations into the former possibility began
in the 1985/6 breeding season by
examining the breeding success of the
penguins, feeding habits, and growth
and survival of chicks. During these
investigations a number of dying
chicks and adults were observed. The
notable feature of these deaths was
that the birds were in good nutritional
condition, with full stomachs-signs
indicative of a very acute disease. Pasteurella multocida was subsequently
isolated at the Central Animal Health
Laboratory from these birds.
Owing to inadequate sampling, a
number of questions remained unanswered as to the exact nature of these
deaths. It was therefore decided to
conduct a detailed study on the diseases of rockhopper penguins in the
1986/7 breeding season. This project
was designed not only to investigate
deaths associated with P. multocida
but also to examine birds for other
bacterial pathogens, viruses, and parasites. The project design had to take
into account the lack of ready access
to frozen storage for the preservation
16 Surveillance 15 (2)
of samples for subsequent mimcrobiological examinations. Department of
Conservation staff were instructed by
MAF veterinarians on post-mortem
technique and the collection and preservation of samples.
In the 198617 breeding seasson the
number of deaths of chicks in the
main study area was less than that in
the previous year. Most appeared to
be due to a combination of trauma,
predation by skuas, and starvation.
However, P. multocida was isolated
from two chicks in the study area.
These birds also had histopathological
findings consistent with an acute septicaemia. Before the start of the 1986/7
breeding season the rats in the study
areas were poisoned to gather further
information on whether they hlad any
adverse effects on the penguin population. No P. multocida were isolated
from the rats, indicating that they may
not be the principal reservoir of
infection.
A limited study in two other
rockhopper penguin colonies where
the rats had not been poisoned
revealed both chicks and adults dying
of septicaemic condition identical to
that observed in the birds from which
P. multocida was isolated. This observation raises the question of whether
the poisoning of the rats in the study
area in some way affected the incidence of deaths due to P. multocida.
No viruses were isolated from samples taken from healthy chicks or
dying birds. However, an RNA
enveloped virus ( 100 nm di4ameter)
was isolated from a pool of ticks
(Ixodes uriue)
which
commonly
parasitise rockhopper penguins. The
significance of this isolate as a cause of
disease in penguins has not been
'determined.
While P. multocida has been
reported to cause large numbers of
deaths in wild birds2 there is imufficient information to determine whether
it has been a significant factor in the
decline in the population of rockhopper penguins on Campbell Island. Further studies are required not only to
assess the significance of the P.
multocida infection but to also determine whether changes in the marine
environment and the penguins' food
supply are a major factor in the
decline in bird numbers.
References
i
Moors, P J, 1986: Decline in numbers of
rockhopper penguins at Campbell Island.
Polar Record, 23: 69-73.
2
Montgomery, R D, Stein, G, Stotts, V D, Settle, F H, 1979: The 1978 epornitic of avian
cholera on the Chesapeake Bay. Avian Diseases, 24: 966-978.
i; W de M e , D J Tisdaii
Veterinary Investigation Officers
MAFQual Central Animal Health Laboratory
Upper Hurt
P J Moors
Department of Conservation
Wellington