Page 507 - Atlas Sea Birds Ver1

numbers of a Globally Threatened species (BirdLife 1987) but subsequently the nature of the evaporation pans
International 2020). Guidelines for the application of IBA changed, they became more flooded and no suitable nesting
criteria recommend that, to meet A1, ‘a site must support: habitat remained (Tom et al. 2024a). Human alteration of
30 individuals (10 Pairs/Reproductive Units) of a species the Orange River Estuary reduced availability of breeding
classified as Vulnerable’ (BirdLife International 2020). habitat there (Anderson et al. 2003). When Hartlaub’s Gulls
In view of this, should the Hartlaub’s Gull be reclassified breed in urban environments, they frequently nest on roofs
as VU, all sites holding ≥ 10 pairs would meet the (Steele 1992). Noise at the colony may disturb residents
guideline for designation as an IBA. Based on the most occupying buildings and nests, feathers, and corpses may
recently available counts at sites there are 24 such sites, block drains and gutters. Therefore, their nests are often
nine in Namibia and 15 in South Africa (Table 2). However, cleared from roofs (Steele 1992). Sometimes chicks are
more recent counts need to be obtained for three sites rescued during such removals and taken to a rescue centre
(Swakopmund Sewage Works, Walvis Bay Bird Paradise, for rehabilitation and are returned to the wild. Nests near
North Long Island) in Namibia and one (Klein Riviers Vlei) airfields were destroyed because of the risk of bird strikes
in South Africa to check that they still hold at least 10 pairs. to air-traffic (du Toit et al. 2003).
Amongst other sites that met the IBA guideline, Northern An expansion of Lüderitz Harbour in the late 1990s,
Mining Pond N83 is a pond that was created by diamond consequent increased activities at the harbour, and a
mining in the southern portion of the Tsau // Khaeb simultaneous, large increase in the numbers of feral cats
(formerly Sperrgebiet) National Park in southern Namibia (Felis catus) around the harbour may have displaced
(Maritz 2024). The region has restricted access but it would Hartlaub’s Gulls from Lüderitz Harbour and Shark Island
require the cooperation of the mining agency to ensure that to breed at Penguin, Seal, and Halifax islands (Tom et
birds breeding at the pond were not disturbed. Of the sites al. 2024b). The joining of Marcus Island to the mainland
identified in South Africa as potential IBAs, at Alexander allowed access by mainland predators and likely led to
Bay Harbour, Hartlaub’s Gulls bred on boats that were not in cessation of breeding there by Hartlaub’s Gulls (Makhado
use, Sandy Point was a fish factory, Saldanha Harbour was et al. 2024). It was thought that a burgeoning feral cat
a commercial port, and areas used for breeding at Cape population at Robben Island displaced Hartlaub’s Gulls
Town waterfront and Sea Point were mainly the roofs of from breeding there in 1997 and 1998 (Crawford and
buildings. These sites are unlikely to prove effective IBAs. Kroese 2000). Hartlaub’s Gulls were infected by highly
Instead, consideration should be given to designating the pathogenic avian influenza (HPAI) (Khomenko et al. 2018)
other 14–18 sites as IBAs and, given that Hartlaub’s Gulls and are likely susceptible to other avian diseases.
often change breeding sites, perhaps also including other In order to secure the future of Hartlaub’s Gulls it will
natural sites that recently supported breeding but not at be important to ensure that safe and undisturbed habitat is
the time of their latest count. provided at natural breeding localities and at sewage works
that support substantial colonies. The most important
Threats colonies are at sewage works in Swakopmund and Walvis
Bay, islands in the vicinity of Lüderitz, Possession Island,
Some suitable breeding habitat for Hartlaub’s Gulls has islands in West Coast National Park, and Dassen, Robben
been lost. Nests on islands in salt and sewage works are and Dyer islands (Table 2). Feral cats should be removed
vulnerable to changing water levels that may flood them or, from Robben Island and all breeding colonies should be
by receding, increase their accessibility to predators. Up protected from human disturbance. Measures to prevent
to 75 pairs of Hartlaub’s Gulls bred at Mile 4 Saltworks, the spread of disease between different breeding localities
north of Swakopmund, in the 1970s and 1980s (Williams should be maintained.

Hartlaub’s gull chick (photo L Upfold )

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