DOI: 10.5061/dryad.vx0k6djp7
title: Data from: The conservation status and population decline of the African penguin deconstructed in space and time

description: Understanding changes in abundance is crucial for conservation, but
 population growth rates often vary over space and time. We use 40 years of
 count data (1979–2019) and Bayesian state-space models to assess the
 African penguin Spheniscus demersus population under IUCN Red List
 Criterion A. We deconstruct the overall decline in time and space to
 identify where urgent conservation action is needed. The global African
 penguin population met the threshold for Endangered with a high
 probability (97%), having declined by almost 65% since 1989. An historical
 low of ~17,700 pairs bred in 2019. Annual changes were faster in the South
 African population (−4.2%, highest posterior density interval, HPDI: −7.8
 to −0.6%) than the Namibian one (−0.3%, HPDI: −3.3 to +2.6%), and since
 1999 were almost −10% at South African colonies north of Cape Town. Over
 the 40-year period, the Eastern Cape colonies went from holding ~25% of
 the total penguin population to ~40% as numbers decreased more rapidly
 elsewhere. These changes coincided with an altered abundance and
 availability of the main prey of African penguins. Our results underline
 the dynamic nature of population declines in space as well as time and
 highlight which penguin colonies require urgent conservation attention.
description: These data are counts of occupied nests of African penguins at 18
 colonies in South Africa and 4 colonies in Namibia. Counting methods are
 detailed in the publication with which this dataset is assocaited. The
 following is text from that publication: "Briefly, counts were
 undertaken by teams of people walking through a penguin colony and
 counting occupied nest sites. Larger colonies were broken down into
 predefined census areas, each of which was counted separately. Counts in
 South Africa were predominately made between February and September each
 year, those in Namibia were made monthly (Crawford et al., 2011; Crawford
 et al., 2013). At some small and difficult to access localities counts
 made outside the main breeding seasons were used if no other count was
 available for that year. Where more than one count was made at a locality
 in a year, the highest count was taken to represent the number of pairs
 breeding that year (Crawford et al., 2011). In Namibia, an occupied site
 was a penguin nest containing fresh eggs or chicks. In South Africa, an
 occupied site was considered active if it contained fresh eggs or chicks,
 or was defended by an adult penguin (or pair of penguins) that were not in
 moult, and considered potential if it was not active but showed recent
 signs of use, e.g. the presence of substantial fresh guano or nesting
 material, the recent excavation of sand from a burrow nest, the presence
 of many penguin footprints in its vicinity, or a combination of these
 factors. Breeding by African penguins is not always synchronous (Crawford,
 Shannon, & Whittington, 1999), so potential nests were counted as
 they may be occupied by pairs that have recently finished breeding or that
 are about to breed (Crawford et al., 2011). Groups of unguarded chicks
 (crèches) were divided by two to estimate the number of nest sites they
 represented (mean clutch size is ~1.8 eggs; Crawford et al., 1999; Shannon
 & Crawford, 1999), with remainders taken to represent an
 additional site, e.g. crèches of five and six chicks would both be taken
 to represent three nests (Shelton et al., 1984)."
description: NA are years in which counts were not conducted, either for
 logistical reasons or because the colony had gone extinct (Lambert's
 Bay after 2005) or not yet been (re)colonised (Robben Island before 1983,
 Stony Point before 1982, Simonstown before 1985). The 0.1 entered at the
 start or end of the time-series at Lambert's Bay, Robben Island,
 Stony Point and Simonstown are for cases where we know that the real
 popualtion size was zero at the either end of the time-series. They were
 entered to 'anchor' the state-space model used in the
 publication with which this dataset is associated to avoid knowingly
 overestimating the population at these sites. They do not represent real
 count data and should be omitted if using these data in some other
 framework.