Long term stability of White-necked Picathartes population in south-east Sierra Leone

Abstract

SummaryWhite-necked Picathartes Picathartes gymnocephalus is a globally 'Vulnerable' bird endemic to the highly threatened Upper Guinea forests in West Africa. In an environment under a high level of threat, the high breeding site fidelity (or breeding site persistence) of this species enables long term monitoring of colony site occupancy, colony size and other breeding parameters, which provide multiple indicators of population status. We surveyed known colony sites and searched for new sites in three recent breeding seasons in order to assess the current population status in the most important part of their range in Sierra Leone, the Gola Forest. We found 157 active nests at 40 colonies, equating to at least 314 adult birds. Less than half of the known colonies were protected by the Gola Forest Reserve. Colonies outside the reserve tended to be confined to larger rocks and subject to disturbance from human activities in close proximity, but did not have fewer active nests in them. Colonies outside the reserve were also more likely to be inactive in a given year whereas all colonies inside the reserve were active in every survey year. A predictive distribution model indicated that the survey region could have as many as 234 nests equating to at least 468 breeding birds. There was no evidence that mean colony size had declined since surveys undertaken in the 1980s and 1990s but it was not possible to compare colony abandonment rates inside and outside the reserve over that time period. Clutch and brood sizes were similar in each year, though brood size appeared slightly lower in the third survey year possibly because of a slightly later survey date. Mean clutch and brood sizes reported during the study period were similar to those found in the 1980s and 1990s. We conclude that the population of White-necked Picathartes in the Gola Forest area has been relatively stable over the last two decades, reflecting both the efficacy of protection afforded by the Gola Forest Reserve and presumably low pressure to farm new areas in the nearby community forest. However, regular monitoring of colonies both inside and outside the reserve is required to detect any systematic impact on the birds as pressure for land increases.

The importance of protected and unprotected areas for colony occupancy and colony size in White-necked Picathartes Picathartes gymnocephalus in and around Gola Rainforest National Park, Sierra Leone

“…However, prior to 2010 protection as a Forest Reserve was mainly in name and levels of protection were little different from the surrounding unprotected community forest until 2010. Earlier work on the same Gola population, using a subset of colonies monitored since 1988, showed stability from 1988 to 2008 (Monticelli et al 2011). This study spanned 11 years of a civil war, 1991-2001, during which time the region saw a reduction in the rural human population reducing pressures on the forest from hunting, logging, farm creation and other subsistence related activities (Lindsell et al 2011).…”

“…Protection within the national park consists of ranger patrols preventing illegal activities such as logging, farming and hunting. Previous analysis from three years of more comprehensive monitoring of this population between 2006 and 2009 showed that colonies in unprotected forest experienced lower levels of colony activity and were more likely to be unoccupied, although colony activity did not differ between protected and unprotected forest (Monticelli et al 2011). Here we use the same data complemented by a further five years of monitoring data to investigate in more detail factors influencing colony occupancy and longer term change in the size of colonies.…”

“…Gola consists of lowland moist evergreen high forest, which in community forest is fragmented by agriculture, and has an altitudinal range of 70-410 m. Rainfall is mainly seasonal, with the wet season extending from May to October, with annual rainfall of 2,500-3,000 mm. Most colonies were also visited and monitored in earlier work (Allport et al 1989, Thompson 1997, Monticelli et al 2011 with five more recently found colonies additionally included in the present study. A further seven historically used colonies, all located outside the national park, were visited annually but had no active nests found in any year of the study and were omitted from all analyses.…”

“…decades and probably much longer. Monitoring numbers of pairs using breeding colonies is the approach taken by most other studies of picathartes (Awa II et al 2009b, Monticelli et al 2011, Atuo et al 2014. In the present study, colonies were visited once during the peak period of breeding activity between October and February.…”

“…At the colony scale we included binary variables that indicated whether evidence of hunting and forest clearance was found. Proximity of colonies to watercourses has previously been identified to be of some importance to breeding picathartes and colony location (Awa II 2008, Monticelli et al 2011) so we included a co-variable describing distance to the nearest stream. As picathartes are forest-dependent for foraging, the proximity of nesting colonies to forest habitat could also be important, especially as colonies are located at traditionally used rock sites and so may persist even when forest habitat is reduced and the forest edge becomes close or adjacent to colonies (Awa II et al 2009a).…”