Migratory strategies dictate stopover ecology, particularly concerning decisions of when, where and how long to stop, and what to do at stationary periods. In birds, individuals stop primarily to ...replenish energy stores, although the functions of stopover events vary among and within species, particularly between pre- and post-breeding seasons. Here, we combined plasma metabolite levels and haematological parameters to compare refuelling rates and physiological state within (early, mid, late) and between (spring, autumn) migratory periods, aiming to identify potentially different migratory strategies in a shorebird, the dunlin Calidris alpina, using a key stopover site in Iberia. Plasma triglycerides and β-hydroxybutyrate concentrations did not differ between seasons, and small differences were found in haematological profiles (higher haemoglobin and hematocrit levels in spring). Similar refuelling rates and physiological status suggests a single migratory strategy in spring and autumn. During both seasons, dunlins arrive at the Tagus estuary with medium-to-high fuel loads, indicating they do not engage in prolonged fuelling. This agrees with a skipping migratory strategy, where birds fly short-to-medium distances while fuelling at moderate rates along a network of sites. Although we may expect late spring migrants to experience stronger pressures to optimally schedule migratory events, we found no significant differences in physiological profiles among early, mid and late migrants. Unexpectedly, such differences were found in autumn: early birds showed the highest triglycerides and haemoglobin levels and lowest β-hydroxybutyrate concentrations. These results denote enhanced refuelling rates and blood oxygen-carrying capacity in early autumn migrants, which is typical of jumpers, i.e., birds travelling with larger fuel loads and performing fewer stops. Our study adds substantially to previous knowledge of stopover ecology in migratory shorebirds in the East Atlantic Flyway. Importantly, it indicates that the Tagus estuary is a high-quality stopover site for intermediate fuelling. Yet, understanding non-fuelling stopping functions is needed to ultimately inform conservation planning.
Migratory shorebird populations are declining worldwide, showing an apparent inability to respond to the interplaying challenges emerging along their flyways. Within the East Atlantic Flyway, ...non-breeding populations show moderate to strong declines in Sub-Saharan Africa, contrasting with stable or increasing trends in Europe. Local factors are insufficient to explain the opposite tendencies and, therefore, investigating migratory strategies and connectivity of these populations may help identifying the drivers of their demography. We followed the migratory journeys of 20 grey plovers (Pluvialis squatarola) from their wintering grounds in Guinea-Bissau (West Africa), Portugal and France (Europe) using tracking devices. Grey plovers wintering in Africa and Europe were found to share breeding grounds at European Russia and Western Siberia, revealing low migratory connectivity in the Eastern Atlantic population. All individuals followed a "skipping" migratory strategy, flying mostly mid-distance bouts, and using an unexpected large network of stopover sites to re-fuel usually for short periods. We identified 66 different stopover sites along the West African, European and Russian/Siberian coasts. All birds stopped at the Wadden Sea in both migratory periods, highlighting the importance of this region and the risk for a potential bottleneck. Low migratory connectivity and similar migratory strategies shared by grey plovers wintering in Europe and West Africa do not support their contrasting population trends.
Shorebirds and seabirds are abundant predators in coastal habitats worldwide, relying upon a high diversity of benthic invertebrates and fish, respectively. While occupying different trophic guilds, ...they are differently exposed to element contamination entering the coastal food web. Therefore, these birds have been used as bioindicators of environmental contamination in marine ecosystems. We analysed the concentration of trace elements in blood samples of 16 shorebird and seabird migratory species in a major non-breeding site, the Bijagós Archipelago, in regard to their trophic ecology. Overall, our study shows low exposure of this bird community to toxic elements, except for Hg. Most species presented Hg burdens within the moderate toxicity threshold, but one species (Dunlin) presented values at a potential high Hg toxicity risk. We found a positive relationship between Se and Ni concentrations and δ15N values (a proxy for trophic level). In addition, a positive relationship was found between δ13C (a proxy for habitat characteristics) and Hg, Fe, Cu and Mn, while the opposite pattern was recorded for As. Differences were also shown for several trace elements between the two studied trophic guilds: concentrations of As, Pb and Se were higher in pelagic fish consumers (seabirds), whereas Cr, Fe and Sr burdens were higher in benthic invertebrate consumers (shorebirds). Although previous studies in the same site revealed very high concentrations of Cd and Pb in some of the prey species of shorebirds and seabirds (bivalves and fishes), values found in birds for these two elements suggest no toxicological risk. Thus, exposure to toxic elements is not currently a threat to coastal bird populations, namely those facing apparent local declines in Guinea-Bissau, one of the most important non-breeding quarters for of West Africa. Still, Hg burdens were high in some species, deserving further monitoring.
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•We present the first trace elements assessment on migratory birds in West Africa.•Most bird species were little exposed to toxic elements in the Bijagós Archipelago.•Dunlins are at a potential high Hg toxicity risk.•Se and Ni significantly increased with δ15N.•As, Pb and Se were higher in seabirds; Cr, Fe and Sr were higher in shorebirds.
We report the concentration of 13 elements in the muscle and liver of 17 coastal fish species of the Bijagós Archipelago, Guinea-Bissau, and link element concentrations to trophic ecology as assessed ...by carbon (δ13C) and nitrogen (δ15N) stable isotopes. We found higher concentrations of Hg, Fe, Mn, Cu, Zn, Se and As in liver as compared to muscle tissue, and the opposite pattern for Sr and Ca in all fish species. The concentration of Hg and Se in muscle samples increased significantly with δ15N, suggesting a biomagnification of these elements in this food chain. The concentrations of Ca and Sr, Fe and Cr, Ca and Mn, and Fe and Mn were positively correlated to each other in more than 50% of the studied species. Fish constitute the most important animal protein source for people in Guinea-Bissau, and thus assessing the concentrations of potentially toxic elements is relevant for human health.
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•We analysed element concentration in muscle and liver concentrations of coastal fish.•Hg, Fe, Mn, Cu, Zn, Se and As concentrations were higher in liver than in muscle.•Sr and Ca concentrations were higher in muscle than in liver.•Hg and Se biomagnified in the food chain.•Several species presented Hg and Pb above the safety limit for human consumption.
Studies providing a detailed diet description of whole-bird communities are surprisingly scarce. Yet, these studies are pivotal to comprehend the mechanisms structuring communities and the ...persistence of each species in the ecosystem. We characterized the diet of a shorebird community in a key non-breeding area of the East Atlantic Flyway, the Bijagós Archipelago (West Africa), combining molecular and morphological prey identification based on 239 droppings from 15 species. Our results show that while relying upon a super-abundant prey (fiddler crab), shorebirds consumed a very high number of taxa. We stress the relevance of highly mobile prey (especially crustaceans but also fish), which typically appear to be of little importance in most shorebird studies. Our results suggest that by consuming a high diversity of prey, shorebirds may reduce competition. This may be critical in a site ranked as the second most important area in West Africa for migratory shorebirds but marked by low benthic invertebrate availability. We further compared the performance of DNA metabarcoding and morphological identification of prey. Overall, molecular and morphological methods combined delivered the most comprehensive results, although molecular methods largely surpassed morphological methods regarding taxonomic detail achieved and number of prey taxa found (4 times more). Taxonomic resolution in the identification of polychaetes and bivalves using the 16S primer was low (mostly to class), whereas this primer clearly performed better than mitochondrial cytochrome c oxidase in identifying more insects and fish. We emphasize the need to increase invertebrate representatives from West Africa in barcode databases, in order to enhance metabarcoding results.
Assessing at-sea distributions and behaviour of seabirds to identify critical foraging sites and spatial overlap with potential threats is a major step for delineating conservation guidelines. The ...West African Crested Tern (
Thalasseus albididorsalis
) is the most abundant breeding tern in West Africa, nesting from Mauritania to Guinea. Its restricted breeding range and exclusive nesting at coastal low-lying areas, place this species at particular risk of losing suitable breeding and resting sites as a consequence of current global changes, namely, sea-level rise. The at-sea distribution of this species is mostly unknown, and therefore, the specific threats faced are still unidentified. Here, we characterize the foraging behaviour and distribution of West African Crested terns breeding at the world’s second-largest colony of the species, in Guinea-Bissau, by tracking 20 individuals. Overall, terns took an average of 2 trips per day, travelling on average 100 km per trip, but often reaching areas up to 120 km from the colony. Shallow waters, usually not exceeding 10 m in depth, and upwelling areas were mostly used as foraging sites. Nocturnal movements, rarely reported on terns, suggest active foraging at night. Key foraging and resting sites were identified, which altogether may regularly hold 2.5–23% of the global breeding population of the West African Crested Tern. These areas are only partly (ca. 50%) covered by the existing marine Important Bird and Biodiversity Area (IBA). Therefore, our results should be considered in any re-evaluation of the IBA borders.
We present the first assessment of the diet of the blackchin guitarfish Glaucostegus cemiculus (Geoffroy Saint-Hilaire, 1817) for West Africa using DNA metabarcoding on stomach contents of ...individuals captured in the Bijagós Archipelago, Guinea-Bissau. The diet was dominated by crustaceans, particularly caramote prawn Penaeus kerathurus (frequency of occurrence FO = 74%, numerical frequency NF = 54%) and fiddler crab Afruca tangeri (FO = 74%, NF = 12%). Bony fishes were present in 30% of the stomachs. We highlight the importance of conservation action for intertidal habitats and their associated benthic invertebrates for the survival of the critically endangered blackchin guitarfish.
Marine fish stocks are increasingly being exploited to unsustainable levels. Yet, knowledge of basic biological and ecological traits of species, required to sustain fisheries management at a local ...scale, remains scarce. We investigated the reproductive biology and growth of two marine catfishes: rough-head sea catfish (Arius latiscutatus) and Guinean sea catfish (Carlarius parkii). Both species showed one spawning season between May and June. Nevertheless, as these are mouth brooding species, we have considered that the reproduction season may be underway until August. Mean fork length of females at first maturity was ∼40 cm for A. latiscutatus and 35 cm for C. parkii, corresponding to 4-5 years for both species. Higher fecundity was found in larger females, with a mean of 45 and 26 eggs for A. latiscutatus and C. parkii, respectively. Differences recorded in sex ratio throughout the year suggest that females can leave the study area after the spawning season or that differences in behaviour may lead to differential sex catchability. The two species showed similar growth curves, despite A. latiscutatus reaching larger lengths at the same age. Estimated length-weight relationships suggest that both species present a positive isometric growth pattern. Our results highlight the slow life-history strategy of the two studied catfish species, thus emphasizing their vulnerability to fishing activities. We suggest that a short-term fishing closure during the spawning period (May-June) in the PNBA may be an important management measure to ensure reproduction opportunities for both species and, therefore, guarantee fishing sustainability.
Agriculture is vital for supporting human populations, but its intensification often leads to landscape homogenization and a decline in non‐provisioning ecosystem services. Ecological intensification ...and multifunctional landscapes are suggested as nature‐based alternatives to intensive agriculture, using ecological processes like natural pest regulation to maximize food production. Birds are recognized for their role in increasing crop yields by consuming invertebrate pests in several agroecosystems. However, the understanding of how bird species, their traits and agricultural land cover influence the structure of bird–pest interactions remains limited. We sampled bird–pest interactions monthly for 1 year, at four sites within a multifunctional landscape, following a gradient of increasing agricultural land cover. We analysed 2583 droppings of 55 bird species with DNA metabarcoding and detected 225 pest species in 1139 samples of 42 bird species. As expected, bird–pest interactions were highly variable across bird species. Dietary pest richness was lower in the fully agricultural site, while predation frequency remained consistent across the agricultural land cover gradient. Network analysis revealed a reduction in the complexity of bird–pest interactions as agricultural coverage increased. Bird species abundance affected the bird's contribution to the network structure more than any of the bird traits analysed (weight, phenology, invertebrate frequency in diet and foraging strata), with more common birds being more important to network structure. Overall, our results show that increasing agricultural land cover increases the homogenization of bird–pest interactions. This shows the importance of maintaining natural patches within agricultural landscapes for biodiversity conservation and enhanced biocontrol.
Resumo
A agricultura é essencial para suportar a população humana, mas a sua intensificação geralmente leva à homogeneização da paisagem e à redução dos serviços do ecossistema que não sejam de provisão. A intensificação ecológica e paisagens multifuncionais são sugeridas como alternativas naturais à agricultura intensiva, utilizando processos ecológicos como a regulação natural de pragas para maximizar a produção de alimentos. As aves são conhecidas pelo seu papel no aumento da produtividade das culturas por consumirem pragas em diversos agroecossistemas. Contudo, o conhecimento de como as espécies de aves, as suas características e a cobertura agrícola influenciam as interações entre aves e pragas são limitados. Nós amostrámos estas interações mensalmente durante um ano, em quatro locais, numa paisagem multifuncional, ao longo um gradiente de aumento da cobertura agrícola. Analisamos 2583 dejetos de 55 espécies de aves com DNA metabarcoding e detetamos 225 espécies praga em 1139 amostras de 42 espécies de aves. Como esperado, as interações entre aves e pragas foram muito distintas entre as várias espécies de aves. A riqueza de pragas na dieta foi menor no local completamente dominado por área agrícola, enquanto a frequência de predação de pragas foi constante ao longo do gradiente de cobertura agrícola. A análise de redes demonstrou uma redução na complexidade das interações entre aves e pragas à medida que a cobertura agrícola aumenta. A abundância das espécies de aves influenciou mais a contribuição das aves para a estrutura da rede do que qualquer uma das características analisadas (peso, fenologia, frequência de invertebrados na dieta e estrato de alimentação), sendo as aves mais comuns as mais importantes na estrutura da rede. De forma geral, os nossos resultados indicam que o aumento da cobertura agrícola aumenta a homogeneização das interações entre aves e pragas. Isto demonstra a importância de preservar áreas naturais em paisagem agrícolas para a conservação de biodiversidade e melhor controlo biológico.
Competition, predation and facilitation shape community structure. Yet facilitative behaviour is poorly studied, especially in marine ecosystems. We investigated the diet and foraging behaviour of 5 ...Afro-Palaearctic migratory seabirds during their non-breeding period in West Africa, focussing on their facilitative associations with predatory fishes. We used next-generation sequencing to describe the diet of 5 tern species, employing DNA metabarcoding for the identification of prey from droppings. This is the first time this method has been used for studying the diet of non-breeding migratory seabirds. Our results showed a high diet overlap among all seabirds, mostly due to the dominance of a single prey species, Sardinella maderensis (with a mean frequency of occurrence of 90% in tern diets). The subsurface marine predators identified in association with terns were crevalle jack Caranx hippos and West African Spanish mackerel Scomberomorus tritor, 2 predatory fishes which also rely on Sardinella maderensis as their most frequent prey in the study area, the Bijagós Archipelago. There were marked inter-specific differences in the reliance of terns on subsurface marine predators as facilitators, ranging from completely independent (little tern Sternula albifrons) to near-obligatory (black tern Chlidonias niger). The varied feeding strategies and small-scale spatial segregation may explain the co-existence of the 5 tern species during the non-breeding period, preying mostly on the same clupeids. Declines both in predatory fishes and in Sardinella maderensis and other clupeids are likely to impact the long-distance migrant seabirds studied here, calling for integrated management of fisheries in these coastal ecosystems.
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