Page 519 - Atlas Sea Birds Ver1

pairs bred in Gauteng. Records listed by Brooke et al.
(1999) suggested that up to 1,434 pairs had bred coastally Important Bird and Biodiversity Areas
(Table 2). Sums of maxima at sites from information
collated for coastal sites indicated that of the order of Important Bird and Biodiversity Areas (IBAs) are identified
1,260 pairs, 657 pairs, 1,670 pairs, 1,391 pairs, and 685 through the use of specific criteria. Regional IBA criterion
pairs may have bred coastally in the 1970s, 1980s, 1990s, B3 applies to sites ‘known or thought to hold, on a regular
2000s, and 2010s, respectively. If gulls moved sites within basis, >= 1% of a biogeographic or other distinct population
periods, these sums of maxima likely overestimated of a congregatory waterbird, breeding seabird or other
abundance. Alternatively, counts not made, or made out species’ (BirdLife International 2020). If Grey-headed
of peak breeding, may have resulted in underestimation of Gulls that breed around the coasts of Namibia and South
numbers. The five decadal totals showed large fluctuations Africa are relatively distinct from birds that nest at inland
but no long-term trend and averaged 1,133 pairs. The sum waterbodies in southern Africa, and if this criterion is
of maxima for the most recent five-year period (2018– applied to a population size of 1,000 pairs (the most recent
2022) was 911 pairs (Table 2) but omitted some sites. The estimate for this populaion), then sites regularly holding
sum of the most recent counts made at sites was 999 pairs ≥ 10 pairs would qualify as regional IBAs. In interpreting
(Table 2) but birds may have bred at multiple sites. Counts ‘regular’ presence, it is important to bear in mind that
made between 2010 and 2020 contributed 93% of the sum Grey-headed Gulls may change their site of breeding. The
of most recent counts, so only 7% of that total is from older most recent counts at sites indicated that Walvis Bay Bird
counts. The coastal population of Namibia and South Africa Paradise, Paarl Sewage Works, Theewaterskloof Dam,
was probably c. 1,130 pairs, which was the approximate Swartkops River valley, Coega River Saltpans, and Lake St
mean of the five decadal estimates. Lucia all held > 1% of, and may qualify as regional IBAs for,
Maxima observed at sites ranged from one pair at each the coastal population (Table 2). However, the most recent
of seven sites to a colony of 1,500 pairs at Lane Island, counts at Walvis Bay Bird Paradise and Theewaterskloof
Lake St Lucia in 1992 (Table 1). The Swartkops River Dam were made in 1984 and 2004, respectively, and so do
valley held 834 pairs in 2022, Walvis Bay Bird Paradise c. not provide up-to-date information. Of the other 23 sites,
500 pairs in 1984, the Coega River Saltpans 436 pairs in ony Rietvlei (11 pairs in 1995) held ≥ 10 pairs (Table 1).
2008, and Bird Island at Lake St Lucia 100 pairs in 2001.
Although counts of nests at Lake St Lucia from 2010–2022 Conservation issues
were lower than in some earlier years, four counts of Grey-
headed Gulls made there between 2014 and 2020 had The population of Grey-headed Gulls breeding around the
values of from 1,232–2,866 birds. Applying a relationship coasts of Namibia and South Africa numbers c. 1,000 pairs
between counts of numbers of birds and counts of nests and is stable. Therefore, from a conservation perspective
derived for Grey-headed Gulls at Lake St Lucia (Fox et al. it is of Least Concern (IUCN 2022). However, it is heavily
2024), the counts of birds suggested that Lake St Lucia’s dependent on the three large, eastern aggregations of the
breeding population was 423–893 pairs from 2014–2022. species at the Swartkops and Coega estuaries entering
The largest colonies observed between Walvis Bay in Algoa Bay and at Lake St Lucia. Colonies at these sites
central Namibia and Algoa Bay at the south of South Africa are reliant on availability of suitable, predator-free nesting
were 40 pairs at Theewaterskloof Dam in 2004, 25 pairs at habitat, which may be influenced by floods, droughts, and
Paarl Sewage Works in both 1993 and 1994, and 23 pairs management practices. Most saltpans in the Swartkops
at De Hoop Vlei in 1961. River valley fall within the Nelson Mandela Bay Metropolitan
Open Space System and are located on land leased from
the Nelson Mandela Bay Municipality. The Redhouse pan
falls within the Zwartkops Valley Local Nature Reserve. The
Coega Saltpans are within the Coega Special Economic
Zone. The Coega Open Space Management Plan protects
areas worthy of conservation from development (Martin
and Whittington 2024). Lake St Lucia falls within the
iSimangaliso Wetland Park.
It is thought that Caracal (Caracal caracal) or Black-
backed Jackal (Canis mesomelas) preyed on the gull
colony at the Coega River Saltpans causing it to relocate to
the Swartkops River valley (Martin and Whittington 2024).
Grey-headed Gulls were infected with highly pathogenic
avian influenza (HPAI) in western South Africa and Uganda
in 2017 and 2018 (Khomenko et al. 2018) and may be
A Grey-headed Gull in breeding plumage (photo BM Dyer) susceptible to outbreaks of other diseases.

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