Reliable predictions for species range changes require a mechanistic understanding of range dynamics in relation to environmental variation. One obstacle is that most current models are static and confound occurrence with the probability of detecting a species if it occurs at a site. Here we draw attention to recently developed occupancy models, which can be used to examine colonization and local extinction or changes in occupancy over time. These models further account for detection probabilities, which are likely to vary spatially and temporally in many datasets. Occupancy models require repeated presence/absence surveys, for example checklists used in bird atlas projects. As an example, we examine the recent range expansion of hadeda ibises (Bostrychia hagedash) in South African protected areas. Colonization exceeded local extinction in most biomes, and the probability of occurrence was related to local climate. Extensions of the basic occupancy models can estimate abundance or species richness. Occupancy models are an appealing additional tool for studying species' responses to global change.

1. Following the discovery in 2007 of non-native spotted bass (Micropterus punctulatus (Rafinesque, 1819)) in the Thee River, Olifants-Doring River system, Western Cape Province, South Africa, a mechanical removal project was initiated in 2010 to eradicate them to protect the unique native fish assemblage in the river. A temporary gabion barrier was constructed to halt spotted bass invasion intoupstream reaches and a variety of mechanical removal techniques were used throughout the project.3. Three hundred and ninety-nine spotted bass were removed from the river during the project. Three hundred (75%) of these were captured by chasing them into gill nets or by catching them with hand nets. The remainder were removed using spearguns, seine nets and by back-pack electrofishing. 4. Spotted bass had been depleted to below detection levels downstream of the temporary barrier in the second year of the project in 2013. A subsequent survey of the river in 2014 revealed a bass population in a reach above the temporary barrier that had previously been considered uninvaded. This population of spotted bass was removed in 2014. Subsequent annual surveys of the Thee River in 2015, 2016 and 2017 have not detected spotted bass and the population is considered to have been extirpated.5. Three years after the extirpation of spotted bass from below the temporary barrier, native fiery redfin (Pseudobarbus phlegethon (Barnard, 1938)) and Cape galaxias (Galaxias zebratus Castelnau, 1861) were observed in pools where they had been absent during the bass invasion.

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SummarySpecies that show obvious population declines are relatively easy to categorize as globally threatened under IUCN Red List criteria. However, species whose populations are highly concentrated at a few inaccessible sites that are unprotected or habitat-threatened and then disperse are more difficult to pigeon-hole. Here we re-assess the conservation status of one such species -the Chestnut-banded Plover Charadrius pallidus -that occurs across Africa in specialized, inaccessible and arid habitat. Wetland bird counts from 1991 to the present allow us to determine a new world population estimate of about 17,830 birds. This allows us to determine a new 1% level and we identified only eight sites in southern and East Africa where these plovers congregate in numbers .1% when non-breeding. There are only five other sites that hold more than 100 birds, indicating that the species is not simply widely dispersed across suitable habitats. Simultaneous counts across southern and East Africa indicate that just three sites -Walvis Bay and Sandwich Harbour in Namibia and Lake Natron in Tanzania -can hold 87% of the world population during non-breeding periods. Since two of these sites are under threat from pollution, siltation and water abstraction, and the eight sites in total comprise just 30% of the area criteria set by IUCN, the bird meets one of the two qualifiers for globally Vulnerable status. Despite this, we cannot detect any long-term declines in population size, partly because of wide variations in population numbers over decadal time periods (itself an IUCN qualifier). It is clear that this bird should move from its present Least Concern status to Near Threatened and conservation measures be enacted at two of the top three sites -Walvis Bay and Lake Natron.