Page 450 - Atlas Sea Birds Ver1

A view from the top of Dassen Island lighthouse of Crowned
Cormorants breeding at its base, 2007 (photo RJM Crawford)

breeding sites for the species: Bird Rock Platform, Ichaboe,
Seal, Halifax, and Possession islands in Namibia and
Meeuw, Dassen, Robben, and Dyer islands in South Africa
(Table 2). Dassen Island held 14% of the sum of the most
recent counts at sites, Possession Island 10%, Meeuw
Island 7%, Bird Rock Platform 6%, and Halifax, Robben,
and Dyer islands each c. 5%. Between them these seven
colonies contributed 51% of that overall total (Table 2).

Conservation issues
Crowned Cormorants are sensitive to human disturbance
at breeding sites and, if displaced from nests, may lose
eggs and chicks to Kelp Gulls (Larus domicanus) (Berry
1974, Crawford et al. 1982, Crawford 1997, Kemper 2015).
They frequently nest in association with other seabirds or
on rocks amongst Cape Fur Seals (Arctocephalus pusillus
Crowned Cormorant feeding its chick (photo BM Dyer) pusillus) to gain protective advantages (Crawford 1997).
However, cessation of breeding at Robbe Island may have
pairs bred from 1977–1981, 1,908 pairs from 2008–2012 resulted from displacement by Cape Fur Seals, as well
(Crawford et al. 2012), 1,974 pairs from 2013–2017,and as increased human disturbance (Crawford et al. 2018).
1,490 pairs from 2018–2022 (Table 2). The decrease Seals may kill fledglings at sea (Cook 2015). All ten species
of 583 (25%) between 2013–2017 and 2018–2022 was of seabird that formerly bred at Marcus Island, including
substantial and mostly attributable to losses of > 100 pairs Crowned Cormorant, ceased to breed there after it was
at both Schaapen and Dassen islands and of 96 pairs at linked to the mainland by a causeway (Makhado et al.
the Danger Point abalone farm. 2024). Mainland colonies of Crowned Cormorants have
Crowned Cormorants have an age at first breeding of been displaced by development, and preyed upon by feral
1–3 years (average 1.75 years, Crawford and Dyer 1996). cats. At islands, nests on the ground near the coast may be
If survival of adult birds (ϕ ) is assumed equivalent to that flooded during storms and incorporation of human debris
α
of Cape Cormorants (0.84 p.a., Crawford et al. 1992), then into nests has caused entanglement and subsequent
generation length (G) may be calculated as: G = A + (1 / death of adults and chicks. Artificial nesting sites such as
(1 − ϕ )) (BirdLife International 2000) = 8 years. Given this platforms, jetties, supports, and ship wrecks may decay and
α
value for G, the recent decrease of 25% over five years in lose their suitability for breeding (Kemper 2015). Pine trees
South Africa equates to 40% in the most recent G. The loss in the town of Lambert’s Bay that were used for breeding
was short term but suggests the South African population were cut down in 2019. In 2006/07, Great White Pelicans
should continue to be regarded as Near Threatened. It will (Pelecanus onocrotalus) fed on Crowned Cormorant
be important to continue monitoring numbers at colonies chicks at Dassen Island, which resulted in fledging success
in order to ascertain whether the recent decrease was a being just 0.08 chicks per pair (Mwema et al. 2010), well
temporary or ongoing phenomenon. below the rate of 1.3 chicks per pair measured by Williams
and Cooper (1983). The 2000 Treasure oil spill caused
Important breeding areas limited mortality of the species at Dassen and Robben
islands (Crawford et al. 2000). Crowned Cormorants also
Between 2018 and 2022, or at their most recent visit, nine are susceptible to outbreaks of disease such as highly
sites held ≥ 100 pairs and should be regarded as important pathogenic avian influenza (Khomenko et al. 2018).

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