The spatial scale of non‐breeding areas used by long‐distance migrant animals can vary from specific, relatively small non‐breeding areas for each independent breeding population (high connectivity) to a distribution over a large non‐breeding area with mixing of breeding populations (low connectivity). Measuring variation in the degree of connectivity and how it arises is crucial to predict how migratory animals can respond to global habitat and climate change because low connectivity is likely to be an adaptation to environmental uncertainty. Here, we assess whether use of non‐breeding areas in a long‐distance migrant may be stochastic by measuring the degree of connectivity, and whether it is annually variable. Twenty‐nine wintering Whinchats tagged with geolocators over 2 years within 40 km2 in central Nigeria were found to be breeding over 2.55 million km2 (26% of the land area of Europe), without an asymptote being approached in the relationship between area and sample size. Ranges differed in size between years by 1.51 million km2 and only 15% of the total breeding range across both years overlapped (8% overlap between years when only first‐year birds were considered), well above the range size difference and below the proportion of overlap that would be predicted from two equivalent groups breeding at random locations within the observed range. Mean distance between breeding locations (i.e. migratory spread) differed significantly between years (604 ± 18 km in 2013 and 869 ± 33 km in 2014). The results showed very low and variable connectivity that was reasonably robust to the errors and assumptions inherent in the use of geolocators, but with the caveat of having only ranges of 2 years to compare, and the sensitivity of range to the breeding locations of a small number of individuals. However, if representative, the results suggest the scope for between‐year variation (cohort effects) to determine migrant distribution on a large scale. Furthermore, for species with similarly low connectivity, we would predict breeding population trends to reflect average conditions across large non‐breeding areas: thus, as large areas of Africa become subject to habitat loss, migrant populations throughout Europe will decline.
The flexibility for migrant land birds to be able to travel long distances rapidly without stopovers, and thus to cross wide inhospitable areas such as deserts and oceans, is likely to be a major determinant of their survival during migration. We measured variation in flight distance, speed and duration of major stopovers (more than 2 days), using geolocator tracks of 35 Whinchats Saxicola rubetra that migrated successfully from central Nigeria to Eastern Europe in spring, and examined how these measures changed, or depended on age, when crossing the barriers of the Sahara or the Mediterranean Sea. In all, 31% of Whinchats crossed at least the Sahara and the Mediterranean before a major stopover and 17% travelled over 4751 km on average without any major stopovers. Flight distance and speed during, and duration of major stopovers after, crossing the Mediterranean Sea were indistinguishable from migration over Continental Europe. Speed during a migration leg was lowest crossing Continental Europe and fastest, with longer duration major stopovers afterwards, when crossing the Sahara, but there was much individual variation, and start date of migration was also a good predictor of stopover duration. As the distance travelled during a leg increased, so major stopover duration afterwards increased (1 day for every 1000 km), but the speed of travel during the leg had no effect. There were no differences in any migration characteristics with age, other than an earlier start date for adult birds. The results suggest that adaptive shortening or even dropping of daily stopovers may occur often, allowing rapid, long-distance migration at the cost of major stopovers afterwards, but such behaviour is not restricted to or always found when crossing barriers, even for birds on their first spring migration. The results may highlight the importance of stopover sites rather than barrier width as the likely key component to successful migration. Individual variation in spring migration may indicate that small passerine migrants like Whinchats may be resilient to future changes in the extent of barriers they encounter, although this may not be true of first autumn migrations or if stopover sites are lost.
A detailed understanding of species’ responses to global climate change provides an informative baseline for designing conservation strategies to optimize protection of biodiversity. However, such information is either limited or not available for many tropical species, making it difficult to incorporate climate change into conservation planning for most tropical species. Here, we used correlative ecological niche models to assess potential distributional responses of 3 range-restricted West African birds, Timneh Parrot (Pscittacus erithracus timneh), Ballman’s Malimbe (Malimbus ballmanni), and White-necked Rockfowl (Picathartes gymnocephalus), to global climate change. We used primary biodiversity occurrence records for each species obtained from the Global Biodiversity Information Facility, eBird, and VertNet; for environmental data, we used climatic variables for the present and future, the latter characterized by 2 IPCC representative concentration pathways (4.5, 8.5) future emissions scenarios and 27 general circulation models for a 2050 time horizon. We found broad present-day potential distributions with respect to climate for all 3 species. Future potential distributions for Ballman’s Malimbe and White-necked Rockfowl tended to be stable and closely similar to their present-day distributions; by contrast, we found marked climate change–driven potential range loss across the range of Timneh Parrot. Our results suggest that impacts of climate change on the present distributions of West African birds will in some cases be minimal, but that individual species may respond differently to future conditions. Thus, to optimize conservation of these species, and of bird diversity in general, we recommend that regional-to-national species conservation action plans incorporate climate change adaptation strategies for individual species; ecological niche models could provide an informative baseline information for this planning and prioritization.
Open-source primary biodiversity data, or digital accessible knowledge (DAK), are widely used in biodiversity informatics to understand the status of global biodiversity, model species’ ecological niches and geographic distributions, and inform biodiversity conservation decisions. However, these datasets are often unavailable, incomplete, or unevenly distributed across regions. We examined DAK for the birds of western Africa, obtained from the Global Biodiversity Information Facility (GBIF) and eBird, to identify gaps in the current knowledge of birds of western Africa, which can be used to guide future avian surveys across the region. We cleaned and standardized the data, resulting in >430,000 records, with 91% from eBird. From these we calculated inventory completeness indices for all grid cells at 0.5°, 0.3°, and 0.1° spatial resolutions across the region. We defined well-surveyed grid cells as those with completeness indices >80% and with >200 associated DAK records. We found marked spatial, seasonal, environmental, and temporal (historical) biases and information gaps in coverage. We identified 59 well-surveyed cells at 0.1°, 55 at 0.3°, and 50 at 0.5° resolution, with well-surveyed sites clustered around points of access such as major cities and national reserves or parks. Our results identified remarkably distinct areas in environmental space with diverse climatic conditions to be given priority for future avian surveys and conservation. The distinctiveness in the climatic conditions of these areas compared to well-surveyed sites is an indication that these areas when sampled could provide new insights into western African bird diversity. Lastly, we show the underrepresentation of traditional biodiversity data (e.g., museums, herbaria collections) compared to citizen science–enabled data (e.g., eBird), which demonstrates the potential of citizen science in documenting and monitoring biodiversity in western Africa, and by extension other poorly known regions of the world.
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