Page 330 - Atlas Sea Birds Ver1

3.3 Numbers, trends, status, and conservation of Leach’s Storm
Petrel (Hydrobates leucorhous) breeding in South Africa

Authors: PA Whittington, JL Visagie, L Upfold, BM Dyer, RJM Crawford, and AB Makhado

Abstract:
Leach’s Storm Petrel (Hydrobates leucorhous) bred in small numbers at two islands off South Africa, and possibly at a third, between
1995 and 2021, and at least one individual Leach’s Storm Petrel was present each summer at a fourth from 1976-1984. The maximum
number recorded in a season was 20 pairs at Dyer Island in 1998, which decreased by 80% to just four pairs at Dassen Island in 2021.
Loss of suitable breeding habitat in an area having low densities of Kelp Gulls (Larus dominicanus) at Dyer Island may have contributed
to the demise of that colony. A lack of such habitat may now limit the South African population, which is Critically Endangered. Migratory
Leach’s Storm Petrels from the North Atlantic visit the Benguela upwelling ecosystem and adjacent waters in their non-breeding season,
the austral summer.

Introduction:
Most Leach’s Storm Petrels (Hydrobates leucorhous) breed in the North Pacific and North Atlantic oceans. The northern populations
migrate south into the tropics in winter, reaching the equator in the Pacific and as far south as south Brazil and South Africa in the Atlantic
(del Hoyo et al. 1992). The species is a common offshore summer visitor to South Africa (Underhill et al. 2002). Some Leach’s Storm
Petrels from colonies off Nova Scotia, Canada, migrated to winter in waters off southern Africa using stopover areas associated with
the Canary and Benguela upwelling ecosystems (Pollet et al. 2019). Petrels from these colonies also travelled substantial distances
(600–1000 km) to feeding grounds in the North Atlantic during incubation (Pollet et al. 2014).
In 2022, the global population of Leach’s Storm Petrels was 6.7–8.3 million breeding pairs, but the species was regarded as Vulnerable
on account of a decline of ≥ 30% over three generations. The cause(s) of the decline were unknown, but were likely multi-faceted and
further research was needed to inform conservation actions (BirdLife International 2022). Leach’s Storm Petrels attain sexual maturity at
five years, occasionally at four years (del Hoyo et al. 1992), annual adult survival ranges from 0.79–0.94, and birds have lived 36 years
in the wild (Huntington et al. 1996). The species is single brooded with a fledging success of 20–57% at colonies in the Pacific Ocean
(Ainley et al. 1990).
Leach’s Storm Petrel was first confirmed breeding in southern Africa (and the Southern Hemisphere) at Dyer Island (Figure 1) in
November 1996 (Whittington et al. 1999). However, 17 birds occupied sites at this island in November 1995, when it was likely that
they bred (Whittington et al. 1999). Subsequently, breeding was also confirmed at Dassen Island and thought to occur at Jutten Island
(Whittington et al. 2001). Earlier, Leach’s Storm Petrel was seasonally recorded ashore at St Croix Island, in Algoa Bay, from 1976–1984
(Randall and Randall 1986) and may have bred there (Underhill et al. 2002).
This chapter collates estimates of numbers of pairs of Leach’s Storm Petrel breeding in South Africa from 1995–2021. It makes a
preliminary, updated assessment of the Red List status of, identifies Important Bird and Biodiversity Areas (IBAs) for, and summarises the
main threats to the South African population.
Numbers and population trend 2005, the petrels have only bred at Dassen Island, where
3–6 pairs nested each season from 2003–2022.
In South Africa, Leach’s Storm Petrel breeds in the austral
summer (Whittington et al. 1999). Presumed numbers of Conservation status, Important Bird and Biodiversity
pairs of Leach’s Storm Petrel breeding at different localities Areas, and threats
from 1995–2021, based on counts of different sites from
which the petrels were calling, were collated in Table 1. In 2015, Leach’s Storm Petrel was classified as Critically
Information was collated from Whittington et al. (1999, Endangered (CR) in South Africa (Taylor and Whittington
2001), Underhill et al. (2002), Crawford et al. (2007), 2015). Numbers breeding in South Africa decreased by
Taylor and Whittington (2015). These were updated with 80% over 23 years from 20 pairs in 1998 to four pairs
unpublished estimates made by CapeNature (CN) and (eight mature individuals) in 2021. Generation length (G)
South Africa’s Department of Forestry, Fisheries and for Leach’s Storm Petrel was estimated to be 13 years
Environment (DFFE). Nests were found at Dyer and (BirdLife International 2022), so the decrease occurred in
Dassen islands and breeding was assumed at Jutten c. 1.77 G and was equivalent to c. 45% in 1 G. Therefore,
Island, where birds were calling in the air around buildings,
from cavities in dry stone walls, and responded to playback
calls and behaved in a similar way to those breeding at
Dyer and Dassen islands (BMD pers. obs).
Maximum numbers thought to have bred in a season
at Jutten, Dassen and Dyer islands were six, five and
20 pairs, respectively (Table 1). Leach’s Storm Petrel
probably bred prior to 1995 at Dyer Island but went
undetected due to its nocturnal habits and to the irregular
and infrequent visits to the island by researchers, who may
not have been familiar with its calls. The largest number
breeding at all localities in a given season was 20 pairs
(all at Dyer Island) in 1998 (Whittington et al. 1999). Since Leach’s Storm Petrel (photo BM Dyer)

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