Page 73 - Atlas Sea Birds Ver1

2.2.3.3 Seabirds breeding at Mile 4 Saltworks, north of Swakopmund

Authors: DB Tom, M Boorman and RJM Crawford

Abstract:
Eight species of seabird have bred at Mile 4 Saltworks, north of Swakopmund, including all five that also did farther north along Namibia’s
Atlantic coastline: Cape Cormorant (Phalacrocorax capensis), White-breasted Cormorant (P. lucidus), Kelp Gull (Larus dominicanus),
Grey-headed Gull (Chroicocephalus cirrocephalus), and Damara Tern (Sternula balaenarum). The additional three species are Hartlaub’s
Gull (C. hartlaubii), Greater Crested Tern (Thalasseus bergii), and Caspian Tern (Hydroprogne caspia). This chapter collates estimates
of numbers of each species breeding at the saltworks. Guano is harvested annually from wooden platforms, which have been used by
large numbers of Cape (> 56,000 pairs in 1998) and White-breasted Cormorant (115 pairs in 1978) for breeding. The saltworks are the
northernmost known locality for breeding by Hartlaub’s Gull and Greater Crested Tern in the Benguela upwelling ecosystem.
Introduction:
Eight species of seabird have bred at Mile 4 Saltworks, north of Swakopmund, including all five that bred farther north along Namibia’s
Atlantic coastline: Cape Cormorant (Phalacrocorax capensis), White-breasted Cormorant (P. lucidus), Kelp Gull (Larus dominicanus),
Grey-headed Gull (Chroicocephalus cirrocephalus), and Damara Tern (Sternula balaenarum). The additional three species are Hartlaub’s
Gull (C. hartlaubii), Greater Crested (Swift) Tern (Thalasseus bergii), and Caspian Tern (Hydroprogne caspia). Records of breeding for
each of the eight seabird species are given below. A short summary of methods used to obtain counts is given in the chapter ‘Introduction
to Seabird Breeding Localities’. ‘√’ signifies breeding occurred but the numbers were not ascertained.
Hartlaub’s Gulls range north to the Cunene River (Simmons et al. 1998) but Mile 4 Saltworks is their northernmost breeding locality
(Williams et al. 1990). Mile 4 Saltworks also is the northernmost recorded breeding locality of the nominate race of Greater Crested Tern
T. b. bergii (Cooper et al. 1990), for which non-breeding records exist for Cape Cross Lagoon, Cunene River Mouth (Simmons et al. 1998),
and Ilha dos Tigres (Dyer 2007). Caspian Terns occur at Cape Cross Saltworks and Cunene River Mouth (Simmons 2015) and have bred
at Ilha dos Tigres (Dyer 2007).
A ninth seabird, Bank Cormorant P. neglectus, attempted breeding at islands in the pans at Mile 4 Saltworks in the 1990s (Simmons et
al. 1998). It was also observed in 1986, in full breeding plumage, manipulating nesting material on concrete structures at the mouth of the
Swakop River (22.67 S; 15.52 E), which was then surrounded by water of the river’s lagoon (Williams 1987). These observations suggest
that the northern limit of breeding by Bank Cormorants at Hollamsbird Island (23.83 S; 14.5 E; Cooper 1981) may be constrained by a
lack of suitable breeding sites farther north. Bank Cormorants have been recorded as far north as Cape Cross (21.77 S; 13.97 E; Williams
1987). Great White Pelicans Pelecanus onocrotalus would probably breed on the platforms at Mile 4 Saltworks but their disruption
of cormorant breeding and their poor-quality guano means they were, and continue to be, dissuaded from breeding at the platforms
(Simmons et al. 1998, M Boorman unpubl.).
In 1998, Mile 4 Saltworks was considered a Namibian, southern African, and global Important Bird Area (Simmons et al. 1998). In
addition to the seabirds that bred there, the saltworks supported large numbers of other waterbirds, including African Black Oystercatcher
(Haematopus moquini). Common (Sterna hirundo) and Black (Chlidonias niger) Terns may be present by day and use the pans as a night
roost. Greater (Phoenicopterus ruber) and Lesser (Phoeniconaias minor) Flamingo occur, the pans forming a staging post for them prior
to departure to their inland breeding areas (M Boorman unpubl.). Chestnut-banded Plovers (Chadarius pallidus) bred at the saltworks, but
their numbers have recently decreased substantially. White-fronted Plovers (Charadrius marginatus) breed year-round at and around the
pans (M Boorman unpubl.).

Description: Mile 4 Saltworks is a 400-ha private nature pans has changed, they have become more flooded, and
reserve and saltworks adjacent to the sea about 7 km there is no longer suitable substrate for them to nest on (M
north of Swakopmund. Salt was formerly collected from Boorman unpubl.). Residential areas have expanded into
a pan known as Panther Beacon. After this salt had been Damara Tern breeding habitat north of Swakopmund that
depleted, seawater was pumped into shallow evaporation lies outside the saltworks (Simmons et al. 2015).
and concentration ponds, from which crystallised salt was
removed. Oysters have been cultivated at the pans since
1985 (Simmons et al. 1998). Wooden platforms that cover
c. 31,000 m were built on one of the northern pans (Berry
2
1976). They are used by cormorants for breeding and the
guano they deposit is collected for sale. Details of guano
yields are given in Tom et al. (2024). Gulls and terns breed
around the pans. In 1986, Greater Crested Terns bred at
an inaccessible islet in the extreme southwestern pan of
the saltworks (Williams 1987). In 1975 and 1976, Caspian
Terns nested on an earth bank adjacent to the main coast
road that was protected by a narrow channel of shallow
water (Clinning 1978). They have also used small, sandy
islands at the saltworks (Simmons 2015). Both Hartlaub’s
Gull and Greater Crested Tern no longer breed at Mile 4 A view of the guano shed at Mile 4, north of Swakopmund, 2007
Saltworks. Over the years the nature of the evaporation (photo RJM Crawford)

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