Page 528 - Atlas Sea Birds Ver1

The largest number estimated to breed at a site was 18000
12,986 pairs at Robben Island. Twelve other sites held > 16000 Benguela upwelling ecosytem
1,000 pairs (maxima are shown after the site name): Dyer
Island (6,722 pairs), Dassen Island (4,946 pairs), Danger 14000
Point Abalone Farm (4,680 pairs), Cape Town waterfront 12000
(4,000 pairs), Malgas Island (3,308 pairs), Schaapen
Island (3,246 pairs), Jutten Island (3,012 pairs), Saldanha 10000
harbour (2,130 pairs), Possession Island (1,678 pairs), Pairs 8000
Ichaboe Island (1,571 pairs), Meeuw Island (1,500 pairs),
and Halifax Island (1,003 pairs). Ichaboe, Halifax, and 6000
Possession islands are in south Namibia and fall within 4000
the Namibian Islands’ Marine Protected Area (NIMPA).
The other ten sites are in southwest South Africa, west 2000
of Cape Agulhas. Malgas, Jutten, and Schaapen islands
are in South Africa’s West Coast National Park (WCNP). 1984 1988 1992 1996 2000 2004 2008 2012 2016 2020
Meeuw Island is adjacent to WCNP and managed as a
conservation area. Dassen and Dyer islands are nature Figure 2. Numbers (pairs) of Greater Crested Terns breeding in
reserves. Robben Island is a National Historical Monument Southern Africa annually, 1984–2022. Not all sites were visited in
that is managed primarily for its historical and cultural every year (see Table 1). Gaps indicate years that lack data for
values and offers less protection to colonies than NIMPA, substantial portions of the overall population
WCNP, and the nature reserves. Saldanha harbour, Cape
Town waterfront, and Danger Point Abalone Farm are not 1987 and 1988 the average number of chicks fledged per
protected. pair was between 0.48 and 0.59 (Crawford et al. 2002).
East of Cape Agulhas, Greater Crested Terns bred at In South Africa, annual survival of Greater Crested Terns
Seal Island (Mossel Bay) in 1923 (Rand 1963) and more in their first year (S ) was 0.52, in their second year (S )
0
1
recently at saltworks in two estuaries and at three islands 0.77 and in their third year (S ) 0.80 (Underhill et al. 1999).
2
in Algoa Bay (Crawford et al. 2009, Martin and Whittington No estimates of adult survival (S ) have been made in
a
2024). the BUS, but in Australia S was assumed to be 0.94 per
a
annum (Dunlop 1985).
Population trend and conservation status The breeding population of T. bergii has fluctuated
substantially but has shown no long-term trend
Numbers of Greater Crested Terns breeding annually (Figure 2) and in 2022 numbered c. 6,900 pairs (> 15,000
in the BUS are shown in Figure 2. They increased from mature individuals). It occurred around the coasts of
<7,000 pairs during 1985–2003 to > 15,000 pairs in 2010 Namibia (c. 1,600 km) and South Africa (c. 3,000 km). It
and 2015. The increase was most plausibly attributed foraged up to 10 km from the coast and occasionally at
to good recruitment and a greater proportion of mature water bodies inland to 3 km (Cooper et al. 1990), so that
birds breeding (Crawford 2003, 2009). An ability to move its geographic range was about 50,000 km . Hence, in
2
between breeding sites (Cooper et al. 1990, Crawford et al. terms of IUCN criteria it would likely be listed as Least
1994) enabled a rapid adjustment to an altered distribution Concern (IUCN 2022).
of prey in the early 2000s (Crawford 2009, Crawford et al.
2014). Important Bird and Biodiversity Areas
The nominate race of Greater Crested Tern first breeds
when aged three years, but may not be fully recruited to Important Bird and Biodiversity Areas (IBAs) are identified
breeding colonies until six years old because many birds do through the use of specific criteria. Regional IBA criterion
not breed in years of food scarcity (Crawford et al. 2002). B3 applies to sites ‘known or thought to hold, on a regular
Breeding success of Greater Crested Terns may vary with basis, >= 1% of a biogeographic or other distinct population
food supply (Chiaradia et al. 2002). At Robben Island, in of a congregatory waterbird, breeding seabird or other
species’ (BirdLife International 2020). If this criterion is
applied to the discrete population of T. b. bergii, then,
based on a population size in 2022 of c. 7,000 breeding
pairs (Figure 1), sites regularly holding ≥ 70 pairs would
qualify as regional IBAs. In interpreting ‘regular’ presence,
it is important to bear in mind the frequent movements
of T. b. bergii between breeding sites. The most recent
counts at nine sites were ≥ 70 pairs: Seal, Penguin, and
Halifax islands in Namibia, Dassen and Robben islands,
Cape Town waterfront, Dyer Island, Chatty Saltpans, and
Seal Island in Algoa Bay (Table 2). Additionally, in the
2010s, counts ≥ 70 pairs were recorded at nine other sites:
Ichaboe Island, Sandy Point, Malgas, Jutten, Meeuw,
Non-breeding Greater Crested Terns (photo L Upfold) and Schaapen islands, Danger Point Abalone Farm, and

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