## 1 Introduction  
Intertidal flats constitute complex transitional systems occurring in the interface between the sea and land. They are estimated to cover at least 127,921 km\({}^{2}\)[1] and include a variety of important habitat types, such as rocky reefs, shell beds, seagrass and macroalgae mats, and soft exposed sediments [2]. Intertidal flats support high biodiversity levels and complex benthic food webs [3], including high-level consumers such as migratory shorebirds, which play an important role in structuring processes in intertidal food webs [4; 5]. These birds depend entirely on intertidal areas for foraging during their non-breeding periods [6], where they congregate at low tide to feed on benthic invertebrate prey [7]. Alarmingly, intertidal areas are declining at an unprecedented rate [1], and shorebirds are experiencing widespread population declines [8; 9], including in the East Atlantic Flyway (EAF; [10; 11]. The causes for these flyway-wide declines are mostly unknown, with insights only for two well-studied species, Bar-tailed godwits _Limosa lapponica_ and Red Knots _Calidris cumtus_, both linked to a reduction in fitness observed in non-breeding areas but caused by global warming effects on breeding sites [12; 13]. Among the main non-breeding sites along the EAF, the Bijagos Archipelago in Guinea-Bissau (West Africa) stands as the third most important area for migratory shorebirds, annually sustaining hundreds of thousands of birds coming from their northern European and Arctic breeding sites [14; 15]. However, as in other sites within the flyway, very steep declines in the populations of several shorebird species have been occurring in the Bijagos Archipelago [16]. Understanding these declines is important in order to expand our knowledge of the extent and the spatial arrangement of intertidal habitats of relevance to shorebirds, especially with regard to their benthic invertebrate prey [17]; to provide the necessary tools to further monitor the impact of ongoing and future changes; and to deepen our understanding of species-habitat relationships. The occurrence, behaviour, and abundance of benthic invertebrate prey in intertidal sediments depends largely on the landscape and sediment characteristics, such as mud and surface water content [18], grain size [19], and elevation [20]. The presence of ecosystem engineers in intertidal flats may also influence the biotic and abiotic components of the ecosystem [21], affecting the benthic invertebrates and shorebirds, as is the case with macoralgae [22] and fiddler crabs [23; 24; 25]. Thus, mapping the distribution of different intertidal sediment types and of these ecosystem engineers in intertidal ecosystems is also essential to better understand the distribution, foraging ecology, and habitat requirements of migratory shorebirds in key non-breeding sites (review in [26]). Applying remote sensing to ecology has become a popular and efficient way to study and characterize the vast and often disiunct intertidal areas that would otherwise be extremely difficult to study and to allow the development of reliable maps of habitats with reduced costs and effort. There are several recent published records aiming at mapping the distribution of intertidal vegetation (e.g., [27; 28; 29], sediment types (e.g., [30; 31; 32], and benthic invertebrate beds [33; 34; 35]. Some studies have also focused on mapping intertidal areas as habitats for shorebirds, but most were solely focused on intertidal vegetation (e.g., [36; 37] or were dedicated to breeding areas [38; 39; 40]. The lack of attention to non-breeding areas along the EAF highlights a significant knowledge gap regarding the distribution and extent of the different intertidal habitats on which shorebirds depend; this is particularly so in tropical regions, which are chronically less studied and understood.