Page 563 - Atlas Sea Birds Ver1

Site Estimated number of breeding pairs Period of 1980s 2000s
From Kolberg Braby RJ estimate 1990s 2010-2021/22
Braby (2011)
(2022) (unpublished) Most recent estimate
Minimum Maximum Minimum Minimum Minimum Year % of total
Wlotzkasbaken 0 17 1 1 2021/22 0.13
Mile 8 3 15 3 2010 0.39
Mile 4 10 20 10 2010 1.29
Horses Graves 30 60 20 20 2014 2.59
Caution Reef 60 100 147 147 2014 19.02
Dolphin Beach 0 32 0 2005 0.00
Donkey Bay, Pelican Point 8 15 8 2009 1.03
Sandwich Harbour 15 35 10 10 2021/22 1.29
Conception Bay 14 50 14 1994 1.81
Meob 18 100 18 1994 2.33
Hottentots Bay 187 300 23 23 2021/22 2.98
Guano Bay 0 1 0 2009 0.00
Grosse Bucht 15 17 15 2009 1.94
Elizabeth Bay 7 10 7 2008 0.91
Possession Island 2 2 2 2008 0.26
Marmora Pan 13 55 5 5 2021/22 0.65
Chameis Pan 1 6 2 2 2021/22 0.26
Single pairs 120 430 120 2010 15.52
Total Angola 6 190 6 0.78
Total Namibia 930 2347 715 92.50
Total South Africa 65 148 52 6.73
Total overall 1001 2685 773 100.00

account for second waves of breeding) of the main generations. This satisfies criterion A3 (“a population
colonies be conducted. Conservation bodies should also reduction ≥ 50% in 3G projected, inferred, or suspected
consider repeating the random sampling surveys across to be met in the future”) of the International Union for
manageable sections of the breeding range, using similar Conservation of Nature (IUCN) for classification as
sampling design to the original random surveys. Endangered (EN, IUCN 2022). However, it should be borne
in mind that the estimate of numbers of adults breeding
Population trends and a re-assessment of the IUCN in 2021/22 is tentative because it is based on limited
conservation status information.
In a scenario where all birds attain adult plumage when
Modal age at first breeding of Damara Terns in Namibia one year old and then have an annual survival of 0.88 and
was 4 years, the youngest observed record being 2 years all breed for the first time when four years old, 47 of 147
and the oldest 15 years (Braby 2011, Braby et al. 2011). birds in adult plumage (c. 32%; cf. the 37% proportion
This somewhat deferred age at breeding accords with non-breeding observed by Simmons et al. 1998) in an
observations in Namibia of three birds ringed as chicks that equilibrium breeding population would be pre-breeders.
returned to their natal sites to breed when aged c. 7 years, Then 3,007 of the minimum number of 4,412 adult-
c. 8 years and c. 9 years (Simmons 2005). In South Africa, plumaged birds estimated to be in Namibia in 1991 (Braby
a chick ringed at Cape Recife in December 2001 was found et al. 1992) would have been breeders, and the decrease
breeding at the Alexandria Dunefields in February 2010, over the next 30 years to 1,442 breeders in 2021/22 would
when aged c. 9 years (Whittington et al. 2015). In Namibia, have been 52%. This is equivalent to a decrease of c. 64%
annual survival of immature birds was estimated to be 0.84 in 3G and, in terms of IUCN’s criterion A2 (“a population
(95% Confidence Interval, CI, 0.64–0.94) and of adults to reduction ≥ 50% in 3G observed, estimated, inferred, or
be 0.88 (95% CI 0.73–0.96) (Braby et al. 2011, 2012).The suspected in the past where the causes of reduction may
mean number of chicks fledged annually per pair was 0.31 not have ceased or may not be understood or may not be
(Braby 2011). These parameters suggested insufficient reversible”) indicates a classification of EN (IUCN 2022).
productivity of Damara Terns to offset adult mortality, even In this instance, not only should uncertainty in the 2021/22
with full participation in breeding, and that the population estimate be borne in mind but also the likelihood (cf.
should decrease (Braby 2011). In 1991, fledging success Simmons 1993, Simmons et al. 1998) that not all flocks of
may have been 0.53 or higher (Braby et al. 1992) and Damara Terns were counted in 1991.
would have been sufficient to maintain the population. In Namibia, in 2015 the Damara Tern was regarded as
Generation length (G) for Damara Terns was calculated Near Threatened and it was noted that a comprehensive
as: G = A + (1/(1 − ϕ )), where A is age at first breeding and survey of the entire breeding population was urgently
α
φ is adult survival (Birdlife International 2000). Following needed to reassess its conservation status (Simmons et al.
α
Braby (2011) and Braby et al. (2011, 2012) we used 2015). In South Africa, Damara Terns recently decreased
A = 4 years and φ = 0.88, which gave G = 12.33 years and (Crawford et al. 2018) and in 2015 the population there
α
3G ~ 37 years. was regarded as Critically Endangered (Simmons 2015).
The estimate of a decrease of c. 23% in the number However, in 2021 IUCN revised its classification of
of adults breeding in Namibia and Angola between 2010 the species from Vulnerable (VU) in 2016 and 2018 to
and 2021/22 equated to a decrease of c. 77% over three Least Concern. This was based upon a range that did

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