Abundance and Population Trends of Gentoo,
by Mike Bingham.
Published 1998 in ORYX 32(3): 223-32.
Rockhopper and King Penguins at the Falkland Islands
The Falkland Islands
are a globally important breeding location for seabirds, including
penguins. The total breeding populations of three of the four main
penguin species present in the Falklands were censused in the austral
summer of 1995/96. The results for gentoo and rockhopper penguins
suggest declines of about 43% and 90% respectively since a similar
census in 1932/33. Recent monitoring studies suggest that these
declines are still continuing; research to investigate causes (likely
to reflect changes in the marine, rather than terrestrial environment)
is a high priority. In contrast king penguin populations, currently
c.400 pairs, have increased steadily, by 700% since 1980/81, in
line with world-wide trends for this species.
The Falkland Islands
lie in the South West Atlantic, approximately 450 km. north east
of the southern tip of South America. The archipelago is made up
of two main islands, and several hundred smaller islands, which
are home to large numbers of breeding seabirds, including penguins.
The Falkland Islands have the world's largest breeding population
of rockhopper penguins (Eudyptes chrysocome chrysocome),
and the second largest population of gentoo penguins (Pygoscelis
papua) (Croxall et al. 1984).
Data gathered from
breeding colonies around the Falklands during the past 10 years,
suggested a decline in the breeding population of gentoo and rockhopper
penguins (Bingham 1995). The only comprehensive island-wide population
census for these species was in 1932/33; a repeat census was needed
to confirm whether declines were occurring throughout the islands,
and to estimate their magnitude. In addition, the census would establish
comprehensive baseline data to complement current monitoring studies.
The imminent exploration for oil in Falklands waters, makes the
establishment of baseline data for these species particularly important,
because of their potential high vulnerability to oil pollution.
The Falklands' population
of king penguin (Aptenodytes patagonicus), is very small,
but was still included in the census. The fourth main Falklands'
penguin, the magellanic penguin (Spheniscus magellanicus),
was not included in this census due to the difficulties of censusing
a species that nests in burrows.
Most breeding site
locations were already known from fieldwork conducted prior to the
1995/96 census; however this information was checked by extensive
consultation with landowners, to ensure that sites were not overlooked.
For a comprehensive
census of such a large area, it was only possible to make a single
visit to each site. Counts made during a single visit will inevitably
underestimate the total number of breeding pairs, because of omitting
pairs that have either not yet laid their eggs, or those that have
already laid and subsequently failed. In general, counts were timed
to correspond with the end of the egg-laying period, thereby ensuring
that few pairs were still to lay, and allowing an assessment to
be made of the underestimate due to pairs failing, by using failure
rates during incubation from other studies.
The gentoo penguins
concluded their first egg-laying by the end of October 1995. The
1995/96 census counted 15% of the gentoo population between 15 -
31 October, and the remainder between 1 November and 1 December.
Because gentoos failing early tend to re-lay, and failure rates
during incubation are low (c.1% per week), the magnitude of any
underestimates resulting from differences in survey dates should
be well below 5%.
are much more synchronous, in terms of egg-laying, than gentoo penguins.
Laying was concluded by mid-November 1995, and the 1995/96 census
counted 98% of the rockhopper population between 1 November - 1
December (2% between 2-18 December). Repeated counts of rockhopper
colonies in previous years showed that nest counts drop at a rate
of about 3% per week for the first month after egg-laying, as a
result of failed nests. It is therefore unlikely that the average
underestimate of rockhopper populations exceeded 10%.
For most rockhopper
and all gentoo breeding sites, the recorder made two separate counts
of all occupied nests using a tally counter. The mean of the two
counts was taken as the number of breeding pairs. Where these two
counts differed by more than 10%, a third count was taken to give
a mean value of three counts. In practice this was rarely necessary,
and the spread of results was generally well below plus or minus
5%. Reference photographs were also taken at most sites for future
For the very large
rockhopper colonies on Steeple Jason, Grand Jason, Bird and Beauchene
Islands, direct ground counts were not possible. These sites were
counted using a total of 60 randomly selected sample plots to determine
the range of nesting densities, and the areas of the colonies was
determined, to enable calculations of total breeding pairs to be
made. A minimum of 10% and a maximum of 15% of the total colony
area was sampled at each of the three sites. These measurements
of area and density taken during the site visits were later compared
against aerial photographs taken of the colonies. The margin of
error for this methodology is greater than for direct counts, but
should be within plus or minus 10%.
The breeding cycle
of the king penguin is different from that of gentoos and rockhoppers,
with chicks over-wintering at the colony, and a complete breeding
cycle lasting over a year. This tends to result in individual birds
having their following breeding cycle out of phase with its predecessor;
thus large chicks and eggs may both occur in a colony at the same
time. This complicates assessment of the breeding populations, and
chick counts were taken instead. The estimation of error for chick
counts is well below 5%, but will underestimate the number of breeding
pairs by about 20% (Lewis Smith & Tallowin 1979).
The 1995/96 census
recorded a total of 339 chicks for the Falklands as a whole. Allowing
for losses during incubation and chick-rearing, and the staggered
breeding cycle, this figure gives an estimated Falklands population
of around 400 breeding pairs. Volunteer Point, on the north-east
coast of East Falkland, was the only king penguin breeding colony
in the Falkland Islands, with individual pairs breeding in gentoos
colonies at all other sites .
The 1995/96 population
of gentoo penguins in the Falkland Islands was about 65,000 breeding
pairs, with an estimated range of 61,750 - 68,250 pairs. There was
a total of 81 breeding sites distributed throughout the archipelago,
ranging in size from 7 to 5100 breeding pairs. Eighteen sites had
breeding populations of >1000 pairs, between them totalling 58%
of the overall population. The general distribution was: East Falkland
- 16,000 pairs (24.5%), West Falkland - 24,000 pairs (37%) and Outer
Islands - 25,000 pairs (38.5%).
The 1995/96 population
estimate for rockhopper penguins in the Falkland Islands was 297,000
breeding pairs, with an estimated range of 267,000 - 327,000 pairs.
There was a total of 36 breeding sites, ranging in size from 83
to 115,000 breeding pairs. These sites are distributed around most
of the Falklands, but the greatest concentrations are on the outer
islands. The general distribution was: East Falkland - 21,000 pairs
(7%), West Falkland -11,000 pairs (4%) and Outer Islands - 265,000
The present Falklands`
population of around 400 breeding pairs is almost entirely concentrated
at one location on the north-east of East Falkland. This colony
has expanded from 38 chicks in 1980/81 (N. Keenleyside, unpublished
data) to 330 chicks in 1995/96. Nevertheless this comprises less
than 0.1% of a world population that has been increasing consistently
since the 1970's (Woehler 1993), and the high rate of increase in
the Falklands during this period is likely to be due in part to
immigration from the large and expanding population on South Georgia.
At least one bird banded on South Georgia has been resighted in
the Falklands (O. Olsen, pers comm).
The Falkland Islands
are one of twelve major breeding sites for this species (Robertson
1986). The 65,000 pairs in the Falklands are widely distributed
throughout the archipelago, and represent about 20% of the world
population; second in size only to South Georgia. Within the Falklands
there are three sites (New Island, Steeple Jason and Saunders Island)
that each hold more than 1% of the estimated world population of
318,000 pairs. However, comparison with Bennett's (1933) total of
116,000 pairs for the Falklands during 1932/33 suggests an overall
decline of around 45%.
Comparison of single
years, widely separated in time, can sometimes be unreliable, especially
in a species whose population shows considerable interannual fluctuation
(Croxall & Rothery, 1995). However, population counts from 21 colonies
which have been monitored since 1988/89 show that the 1995/96 census
did not coincide with a season of especially low population. Moreover,
these data suggest that the decline has been continuing in recent
years. Although no records exist as to the methodology employed
during Bennett's (1933) census, his numerous publications testify
to his reputation as a meticulous and experienced observer and naturalist,
and gentoo penguins are a particularly easy species to count accurately.
Even if the larger and hence more difficult sites such as the Jason
Islands are excluded, comparable counts for the remaining sites
still indicate a decline over the 60 year period.
The Falklands population,
of around 300,000 pairs, represents the world's most important breeding
site for this species. In addition, the Falkland Islands have 63%
of the world population for this sub-species, with most of the remainder
being on islands around the coast of Chile (Bingham and Mejias,
In press). In the Falklands, the islands of Steeple Jason and Grand
Jason to the north-west, and Beauchene to the south, hold the only
very large concentrations (> 20,000 pairs) and these account for
around 75% of the Falklands population.
from study sites monitored throughout the 1990's show that the 1995/96
census did not coincide with a year of naturally low populations.
Thus the current population estimate is very considerably lower
than the 3,169,000 pairs recorded by Bennett (1933) in 1932/33.
Although Bennett gave no account of the methodology used, he states
that his figures were most likely to be underestimates, and did
not include the large colonies on Beauchene and Bird Island which
currently hold 28% of the Falklands population. It therefore appears
that the Falklands population has declined to about 10% of its 1932/33
of king penguins in the Falklands have increased in recent years,
in line with world-wide trends, populations of gentoo and rockhopper
penguins have decreased substantially over the last 60 years, perhaps
by as much as 50% and 90% respectively. This is supported by data
from more recent site studies which also suggest that the declines
have continued into recent years. Kidney Island's rockhopper population
declined from 3,000 pairs in 1960/61 to 240 pairs in 1994/95 (Bingham
1995), rockhopper colonies at New Island declined from >100,000
pairs in 1976/78 to 4,000 pairs in 1992 (Thompson 1993), and at
Beauchêne Island the colony had declined from 300,000 pairs in 1980
(Lewis-Smith and Prince 1985) to 71,500 pairs in 1991 (Thompson
1993). The 1985/86 summer season was especially bad for rockhoppers,
with tens of thousands of adults dying from starvation during their
annual moult. Analysis of carcasses showed that they had died from
starvation, and this was likely to have resulted from food shortages
prior to the moult (Keymer, 1988).
It is not easy to
account for these declines. Direct exploitation of penguins has
diminished to insignificance. Killing birds to extract oil ceased
at the beginning of the 20th century, and collecting of eggs for
food has now declined to very low levels.
started around the Falklands in the 1960's, expanded greatly during
the 1970's and 1980's, and in recent years has been generally stable
since the Falkland Islands Government imposed a licensing regime
in 1985. There is some evidence that penguin population size and
breeding performance is related to food availability around the
Falklands (Keymer, 1988; Thompson, 1989,1993; Bingham, 1995). There
is no direct evidence that food availability to penguins has been
affected by commercial fishing, but this possibility cannot be ruled
out, especially in respect of squid fisheries, larval/juvenile squid
being an important element of the diet of both rockhopper and gentoo
penguins (Thompson 1994). It should also be noted that the breeding
season diet of rockhoppers, appears to comprise of more Euphausids
and less commercially fished species than that of the gentoo (Thompson
Loss or degradation
of breeding habitat has probably occurred at some sites. due to
erosion, fire or other anthropogenic activity. Disturbance from
humans and stock may also have been (and remains) a problem in some
areas, though there is little firm evidence that this or the current
level of tourist visits have any discernible influence. Overall,
none of these effects can explain large scale changes, especially
at sites where breeding habitat loss and disturbance have been minimal
or non-existent. There is also no evidence of increased impact from
introduced predators, and many sites lack any introduced predatory
(of the subspecies E.c. filholi) have declined very substantially
at the New Zealand Sub-Antarctic islands since the 1940's (Cunningham
& Moors 1994, Cooper 1992). At these sites also there was no evidence
that land-based influences were responsible. It was therefore suggested
that changes in the marine environment may have occurred and affected
the survival of penguins, either directly through physical factors
or, more likely, indirectly through changes to the food web.
At a recent international
workshop reviewing the status of penguins, it was clear that the
large-scale declines in rockhopper penguin populations were of such
magnitude as to justify treating the species as globally threatened
(Vulnerable), according to the new IUCN criteria. A co-ordinated
programme of research on this species at its most important population
site, the Falkland Islands, is now long overdue.
My thanks go to
the RAF Ornithological Society, and other dedicated volunteers who
assisted with the surveys, the Commander, British Forces Falkland
Islands, for arranging logistical support and aerial photographs,
the Wellcome Trust for funding the project, and Dr. John Croxall
for assisting with drafting the manuscript. Thanks to all the landowners
who, virtually without exception, offered support in providing information,
assistance and access to their land.
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