Robin C. Whytock

Do large birds experience previously undetected levels of hunting pressure in the forests of Central and West Africa

The commercial bushmeat trade threatens numerous species in the forests of West and Central Africa. Hunters shoot and trap animals, which are transported to rural and urban markets for sale. Village-based surveys of hunter offtake and surveys of bushmeat markets have shown that mammals and reptiles are affected most, followed by birds. However, hunters also consume some animals in forest camps and these may have been overlooked in surveys that have focused on bushmeat extracted from the forest. A number of studies have used indirect methods, such as hunter diaries, to quantify this additional offtake but results can be difficult to verify. We examined discarded animal remains at 13 semi-permanent hunting camps in the Ebo Forest, Cameroon, over 272 days. Twenty-one species were identified from 49 carcasses, of which birds constituted 55%, mammals 43% and other taxa 2%. The mammals identified were typical of those recorded in previous bushmeat studies but we recorded several species of birds rarely recorded elsewhere. Offtake of bird species increased with mean body mass. We extrapolated our results to the 34 known hunting camps in the Ebo Forest and estimated that a minimum of 97 birds are hunted annually in a catchment area of c. 479 km2. We conclude that some bird species may be hunted more frequently than previous research suggests and this has important conservation implications for larger-bodied species such as raptors and hornbills.

Trade of threatened vultures and other raptors for fetish and bushmeat in West and Central Africa

Diurnal raptors have declined significantly in western Africa since the 1960s. To evaluate the impact of traditional medicine and bushmeat trade on raptors, we examined carcasses offered at markets at 67 sites (1–80 stands per site) in 12 countries in western Africa during 1990–2013. Black kite Milvus migrans and hooded vulture Necrosyrtes monachus together accounted for 41% of 2,646 carcasses comprising 52 species. Twenty-seven percent of carcasses were of species categorized as Near Threatened, Vulnerable or Endangered on the IUCN Red List. Common species were traded more frequently than rarer species, as were species with frequent scavenging behaviour (vs non-scavenging), generalist or savannah habitat use (vs forest), and an Afrotropical (vs Palearctic) breeding range. Large Afrotropical vultures were recorded in the highest absolute and relative numbers in Nigeria, whereas in Central Africa, palm-nut vultures Gypohierax angolensis were the most abundant vulture species. Estimates based on data extrapolation indicated that within West Africa 73% of carcasses were traded in Nigeria, 21% in Benin and 5% elsewhere. Offtake per annum in West Africa was estimated to be 975–1,462 hooded vultures,356–534 palm-nut vultures, 356–534 Ruppell’s griffons Gyps rueppellii, 188-282 African white-backed vultures Gyps africanus, 143-214 lappet-faced vultures Torgos tracheliotos, and 40–60 crowned eagles Stephanoaetus coronatus. This represents a sizeable proportion of regional populations, suggesting that trade is likely to be contributing significantly to declines. Stronger commitment is needed, especially by governments in Nigeria and Benin, to halt the trade in threatened raptors and prevent their extirpation

Bird‐community responses to habitat creation in a long‐term, large‐scale natural experiment

Ecosystem function and resilience are compromised when habitats become fragmented due to land-use change. This has led to national and international conservation strategies aimed at restoring habitat extent and improving functional connectivity (i.e., maintaining dispersal processes). However, biodiversity responses to landscape-scale habitat creation and the relative importance of spatial and temporal scales are poorly understood, and there is disagreement over which conservation strategies should be prioritized. We used 160 years of historic post-agricultural woodland creation as a natural experiment to evaluate biodiversity responses to habitat creation in a landscape context. Birds were surveyed in 101 secondary, broadleaf woodlands aged 10-160 years with ≥80% canopy cover and in landscapes with 0-17% broadleaf woodland cover within 3000 m. We used piecewise structural equation modeling to examine the direct and indirect relationships between bird abundance and diversity, ecological continuity, patch characteristics, and landscape structure and quantified the relative conservation value of local and landscape scales for bird communities. Ecological continuity indirectly affected overall bird abundance and species richness through its effects on stand structure, but had a weaker influence (effect size near 0) on the abundance and diversity of species most closely associated with woodland habitats. This was probably because woodlands were rapidly colonized by woodland generalists in ≤10 years (minimum patch age) but were on average too young (median 50 years) to be colonized by woodland specialists. Local patch characteristics were relatively more important than landscape characteristics for bird communities. Based on our results, biodiversity responses to habitat creation depended on local- and landscape-scale factors that interacted across time and space. We suggest that there is a need for further studies that focus on habitat creation in a landscape context and that knowledge gained from studies of habitat fragmentation and loss should be used to inform habitat creation with caution because the outcomes are not necessarily reciprocal.

Bird-community responses to habitat creation in a long-term, large-scale natural experiment (Forthcoming/Available Online)

Ecosystem function and resilience are compromised when habitats become fragmented due to land-use change. This has led to national and international conservation strategies aimed at restoring habitat extent and improving functional connectivity (i.e., maintaining dispersal processes). However, biodiversity responses to landscape-scale habitat creation and the relative importance of spatial and temporal scales are poorly understood, and there is disagreement over which conservation strategies should be prioritized. We used 160 years of historic post-agricultural woodland creation as a natural experiment to evaluate biodiversity responses to habitat creation in a landscape context. Birds were surveyed in 101 secondary, broadleaf woodlands aged 10-160 years with ≥80% canopy cover and in landscapes with 0-17% broadleaf woodland cover within 3000 m. We used piecewise structural equation modeling to examine the direct and indirect relationships between bird abundance and diversity, ecological continuity, patch characteristics, and landscape structure and quantified the relative conservation value of local and landscape scales for bird communities. Ecological continuity indirectly affected overall bird abundance and species richness through its effects on stand structure, but had a weaker influence (effect size near 0) on the abundance and diversity of species most closely associated with woodland habitats. This was probably because woodlands were rapidly colonized by woodland generalists in ≤10 years (minimum patch age) but were on average too young (median 50 years) to be colonized by woodland specialists. Local patch characteristics were relatively more important than landscape characteristics for bird communities. Based on our results, biodiversity responses to habitat creation depended on local- and landscape-scale factors that interacted across time and space. We suggest that there is a need for further studies that focus on habitat creation in a landscape context and that knowledge gained from studies of habitat fragmentation and loss should be used to inform habitat creation with caution because the outcomes are not necessarily reciprocal.

Wood Warbler Phylloscopus sibilatrix nest provisioning rates are correlated with seasonal caterpillar availability in British Oak Quercus woodlands

Capsule Maximum provisioning rates occurred during the seasonal peak in caterpillar availability, controlling for brood age and time of day. Aims To determine if the seasonal availability of caterpillars influenced Wood Warbler Phylloscopus sibilatrix nest provisioning rates. Methods Remote cameras were used to monitor nest visits at 14 nests in 8 British oak Quercus woodlands during 2013. The timing of the caterpillar peak was estimated by monitoring the production of caterpillar faecal pellets under oak trees. Results Maximum provisioning rates occurred when the date of provisioning coincided with the date of peak caterpillar availability, but the percentage change in provisioning rates during asynchrony was dependent on brood age. Younger broods experienced a greater decline in provisioning rates than older broods during asynchrony. Provisioning rates peaked in the morning and declined during the day, but when caterpillar availability was low there was little within-day variation. Conclusion Provisioning rates show seasonal variation that is correlated with caterpillar availability. Previous studies suggest that Wood Warbler reproductive fitness is independent of synchrony between the breeding cycle and the caterpillar peak, however, the implications for adult fitness are unknown and should be investigated further.

Tritrophic phenological match–mismatch in space and time

Increasing temperatures associated with climate change may generate phenological mismatches that disrupt previously synchronous trophic interactions. Most work on mismatch has focused on temporal trends, whereas spatial variation in the degree of trophic synchrony has largely been neglected, even though the degree to which mismatch varies in space has implications for meso-scale population dynamics and evolution. Here we quantify latitudinal trends in phenological mismatch, using phenological data on an oak–caterpillar–bird system from across the UK. Increasing latitude delays phenology of all species, but more so for oak, resulting in a shorter interval between leaf emergence and peak caterpillar biomass at northern locations. Asynchrony found between peak caterpillar biomass and peak nestling demand of blue tits, great tits and pied flycatchers increases in earlier (warm) springs. There is no evidence of spatial variation in the timing of peak nestling demand relative to peak caterpillar biomass for any species. Phenological mismatch alone is thus unlikely to explain spatial variation in population trends. Given projections of continued spring warming, we predict that temperate forest birds will become increasingly mismatched with peak caterpillar timing. Latitudinal invariance in the direction of mismatch may act as a double-edged sword that presents no opportunities for spatial buffering from the effects of mismatch on population size, but generates spatially consistent directional selection on timing, which could facilitate rapid evolutionary change.Most work on phenological mismatch has focused on temporal trends only. Here, the authors analyse trends in spatial and temporal mismatch between trees, caterpillars and birds in the UK, and find delayed phenology of all species with increasing latitude and little spatial variation in the magnitude of mismatch between caterpillars and birds.

Context-dependent colonization of terrestrial habitat ‘islands’ by a long-distance migrant bird

Landscape context can affect how individuals perceive patch quality during colonization. However, although context-dependent colonization has been observed in aquatic environments, it has rarely been studied in terrestrial environments or at large spatial scales. In this paper, we assessed how landscape context influenced colonization rates in a large-scale (ca 7000 km2) terrestrial system where colonizers (Willow Warbler Phylloscopus trochilus) are capable of rapid, long-distance movements. Bioacoustic recorders were used to detect first song dates (an indicator of colonization or re-colonization) and settlement in 23 naturally replicated habitat patches. We compared support for three competing hypotheses describing colonization patterns that depend on landscape context (‘redirection’, ‘landscape-selection’ and ‘relative patch size’) with two patch-level hypotheses (patch ‘quality’ and ‘heterospecific attraction’). First song was earlier when habitat availability in the landscape was low, supporting the ‘redirection’ hypothesis. Settlement probability was best predicted by patch ‘quality’ and was lower in woodlands with a dense understorey. Results suggest that colonization of habitat patches by male P. trochilus after spring migration is spatially hierarchical. First, initial colonization depends on landscape context, and settlement is then determined by fine-scale vegetation characteristics. More broadly, we suggest that patterns observed in fragmented aquatic environments (e.g. ‘redirection’) can, in some circumstances, be extended to large-scale terrestrial environments.

Invasion legacy effects versus sediment deposition as drivers of riparian vegetation

Riparian zones are formed by interactions between fluvio-geomorphological processes, such as sediment deposition, and biota, such as vegetation. Establishment of invasive alien plant (IAP) species along rivers may influence vegetation dynamics, evidenced as higher seasonal or inter-annual fluctuations in native plant diversity when IAP cover is high. This could impact the overall functioning of riparian ecosystems. Conversely, fine sediment deposited in riparian zones after floods may replenish propagule banks, thus supporting recruitment of native species. The interactive effects of invasion and fine sediment deposition have hitherto, however, been ignored. Vegetation surveys across rivers varying in flow regime were carried out over 2 years to assess changes in community composition and diversity. Artificial turf mats were used to quantify over-winter sediment deposition. The viable propagule bank in soil and freshly deposited sediment was then quantified by germination trials. Structural Equation Models were used to assess causal pathways between environmental variables, IAPs and native vegetation. Greater variation in flow increased the cover of IAPs along riverbanks. An increased in high flow events and sediment deposition were positively associated with the diversity of propagules deposited. However, greater diversity of propagules did not result in a more diverse plant community at invaded sites, as greater cover of IAPs in summer reduced native plant diversity. Seasonal turnover in the above-ground vegetation was also accentuated at previously invaded sites, suggesting that a legacy of increased competition in previous years, not recent sediment deposition, drives above-ground vegetation structure at invaded sites. The interaction between fluvial disturbance via sediment deposition and invasion pressure is of growing importance in the management of riparian habitats. Our results suggest that invasion can uncouple the processes that contribute to resilience in dynamic habitats making already invaded habitats vulnerable to further invasions.

Habitat characteristics of wintering Wood Warbler Phylloscopus sibilatrix in the Centre Region of Cameroon: conservation implications

Populations of many Afro-Palearctic birds have declined, with those wintering in sub-Saharan Africa, such as Wood Warbler Phylloscopus sibilatrix, particularly affected. In this study we investigated the relationship between habitat characteristics and Wood Warbler presence/absence in the Centre Region of Cameroon. A total of six transects were established in three habitat types (forest, forest–savanna transitional zone and savanna). Call playback surveys were conducted monthly from November 2015 to April 2016 to determine Wood Warbler presence/absence. Detailed habitat measurements were also recorded in each transect. A total of 86 responses were recorded: 33 (mean 6.6 ± 2.3) in forest habitat, 47 (mean 9.4 ± 3.36) in the forest–savanna transitional zone, and 6 (mean 2 ± 1.1) in savanna habitat. Wood Warbler presence increased significantly with the number of trees between 3 and 7 m in height, and decreased significantly with the number of shrubs between 0.5 and 3 m in height. Anthropogenic disturbance such as the agricultural cycle and burning were not found to have an effect on Wood Warblers presence/absence. We conclude that Wood Warblers overwinter in all three habitat types with probability of detection greatest in the forest–savanna transitional habitat with a relatively low canopy and an open understorey. Forest clearance in sub-Saharan Africa potentially threatens wintering habitat for Wood Warblers.