Shorebirds are capable of flying extraordinary distances so why might some species stay put? Whereas some plover species disperse so widely that populations remain connected over thousands of kilometres, our new study highlights one species whose sedentary behaviour has led to long-term isolation in southern and eastern Africa. Using DNA analyses, we identified deep differentiation between the two subspecies of Chestnut-banded Plover (Charadrius pallidus pallidus of Namibia and Charadrius pallidus venustus of Kenya and Tanzania).
As many as 87% of Chestnut-banded Plovers congregate in just three locations during the non-breeding season (Walvis Bay and Sandwich Harbour in Namibia, and Lake Natron in Tanzania). Their limited dispersal is thought to be linked to two key behaviours. Firstly, these plovers are habitat specialists that prefer saline or alkaline wetland without vegetation, but such habitat is lacking for 2,000 km between their eastern and southern African populations (between central Tanzania and Northern Botswana). Secondly, Chestnut-banded Plovers are monogamous and therefore more likely to breed at the same site year after year, whereas polygamous shorebird species tend to be less site-faithful, often relocating between breeding attempts.
We suspect the isolation of these plovers in southern and eastern Africa first occurred due to geological and environmental changes during the last few million years. However, their continued separation is driven by their behaviour, resulting in unusually strong genetic divergence for a plover species across mainland Africa. While our data supports an evolutionary split between the two subspecies (C. p. pallidus and C. p. venustus), further study across their full geographic range should be carried out before considering these as separate species.
Regardless of their taxonomic status, the genetic differentiation we found indicates that C. p. pallidus and C. p. venustus ought to be managed as independent units rather than as a combined Africa-wide population. Of particular concern is C. p. venustus of eastern Africa, where only four sites hold more than 100 individuals (Lake Natron, Lake Masek and Lake Manyara in Tanzania and Lake Magadi in Kenya). With confirmation that these plovers are genetically as well as geographically distinct from their southern counterparts, it is all the more important to protect their wetland homes as these specialist shorebirds may not be capable of re-locating elsewhere if these sites become untenable.
N. dos Remedios, Küpper, T. Székely, N. Baker, W. Versfeld & P.L.M. Lee. 2017. Genetic isolation in an endemic African habitat specialist. Ibis 159: 792–802.