Assessing distribution, abundance and impacts of trade and habitat change in western populations of African grey parrot (psittacus erithacus)

Annorbah, Nathaniel N.D (2016) Assessing distribution, abundance and impacts of trade and habitat change in western populations of African grey parrot (psittacus erithacus). Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

In Ghana, many large avian frugivores face very serious threats, including habitat loss, hunting, and capture for the pet trade. However, basic ecological information is lacking for most species including the heavily-traded Grey Parrot Psittacus erithacus. The aim of my PhD was therefore to investigate the current distribution, abundance and ecology of Grey Parrot and other large frugivores to help inform their future conservation. I conducted surveys for twenty species of pigeons, parrots, turacos and hornbills in forty-two 10 km × 10 km survey squares in southwest Ghana. Only two species, West African Pied Hornbill Lophoceros semifasciatus and African Green Pigeon Treron calvus, were recorded in most survey squares. The most restricted and rare species included large-bodied species such as Great Blue Turaco Corythaeola cristata, Yellow-casqued Hornbill Ceratogymna elata and Black-casqued Hornbill C. atrata. Canonical Correspondence Analysis showed that large hornbills were especially restricted to large forest reserves with low anthropogenic disturbance. I then used Maxent to predict more precisely the distribution of the frugivores across Ghana, and identify their responses to predictors such as land cover types, enhanced vegetation index (EVI), human population density, and climate data. Frugivores showed varying associations with Ghana’s large forest reserves, with Afep Pigeon Columba unicincta, Great Blue Turaco, and Black Dwarf Hornbill Tockus hartlaubi among the most restricted. Most species had highest occurrence probabilities in the southwest of the country. The main driver of distributions was land cover type, with forest habitats preferred in 90% of species. Differences in human population density and EVI were seldom important. The large southwestern forest reserves are key sites for Ghana’s frugivores, and it is crucial that they are adequately protected and managed. Grey Parrot is believed to have undergone rapid population decline, yet there are almost no quantitative data properly supporting this from anywhere within its huge range. I reviewed its historical abundance across Ghana, undertook targeted searches across the country’s forest zone, repeated counts at 22 parrot roosts first performed two decades ago and gauged around 900 people’s perceptions of the decline and its causes. In over 150 days of fieldwork, just 32 groups were recorded. Encounter rates were 15 times lower than those from the early 1990s. No active roosts, i.e. roosts in current use, were found, and just a handful of birds seen near three roosts that each harboured 700–1200 birds two decades ago. Interviewees stressed the importance of very tall trees of commercially important timber species for nesting and roosting. Ghana has lost 90–99% of its Grey Parrots since 1992, and there is no evidence that, away from one or two localities, declines are less severe anywhere else in West Africa. Despite declines, Grey Parrots paradoxically remain reasonably widely distributed. I developed multiple historical and current Maxent models for the species based on various presence data sources: field surveys from the early 1990s and 2012–14, records from the Global Biodiversity Information Facility, and interview data. Models of historical distribution showed high suitability over much of the study area. Current distributions were predicted to be much more patchy, with large areas unsuitable, but with high suitability in the extreme south/southwest. Historically, Grey Parrot distribution was correlated most strongly with high rainfall, while current distribution is more closely linked with land use. Levels of exploitation of Grey Parrots have been unsustainable and regulation of the trade through quota schemes and enforcement of trade embargoes needs to be strengthened. Ghana should also reintroduce shade cocoa agriculture to improve habitat quality for the Grey Parrot and other frugivores.