Connectivity at the human-wildlife interface: starling movements relate to carriage of E. coli

Synanthropic bird species in human, poultry or livestock environments can increase the spread of pathogens and antibiotic-resistant bacteria between wild and domestic animals. We present the first telemetry-based spatial networks for a small songbird. We quantified landscape connectivity exerted by spotless starling movements, and aimed to determine if connectivity patterns were related to carriage of potential pathogens. We captured 28 starlings on a partridge farm in 2020 and tested them for Avian influenza virus, West Nile virus WNV, Avian orthoavulavirus 1, Coronavirus, Salmonella spp. and Escherichia coli. We did not detect any viruses or Salmonella, but one individual had antibodies against WNV or cross-reacting Flaviviruses. We found E. coli in 61 % (17 of 28) of starlings, 76 % (13 of 17) of which were resistant to gentamicin, 12 % (2 of 17) to cefotaxime/enrofloxacin and 6 % (1 of 17) were phenotypic extended spectrum beta-lactamase (ESBL) carriers. We GPS-tracked 17 starlings and constructed spatial networks showing how their movements (i.e. links) connect different farms with nearby urban and natural habitats (i.e. nodes with different attributes). Using E. coli carriage as a proxy for acquisition/dispersal of bacteria, we found differences across spatial networks constructed for E. coli positive (n = 7) and E. coli negative (n = 9) starlings. We used Exponential Random Graph Models to reveal significant differences between networks. In particular, an urban roost was more connected to other sites by movements of E. coli positive than by movements of E. coli negative starlings. Furthermore, an open pine forest used mainly for roosting was more connected to other sites by movements of E. coli negative than by movements of E. coli positive starlings. Using E. coli as a proxy for a potential pathogen carried by starlings, we reveal the pathways of spread that starlings could provide between farms, urban and natural habitats.

Leakage of plastics and other debris from landfills to a highly protected lake by wintering gulls

GENERAL CONTEXT

Gulls ingest plastic and other litter while foraging in open landfills, because organic matter is mixed with other debris. Therefore, gulls are potential biovectors of plastic pollution into natural habitats, especially when they concentrate in wetlands for roosting.

NOVELTY

We quantified, for the first time, the flow of plastic and other anthropogenic debris from open landfills to a natural lake via the movement of gulls. We focused on Fuente de Piedra, an inland closed-basin lake in Spain that is internationally important for biodiversity.

METHODOLOGY

In 2022, we sampled gull pellets regurgitated in the lake by lesser black-backed gulls Larus fuscus that feed on landfills, as well as their faeces, then characterized and quantified debris particles of ≥0.5 mm. By combining GPS and census data from 2010 to 2022, together with plastic quantification based on FTIR-ATR analysis, we estimated the average annual deposition of plastic and other debris by the wintering gull population into the lake.

MAIN RESULTS

86 % of pellets contained plastics, and 94 % contained other debris such as glass and textiles. Polyethylene (54 %), polypropylene (11.5 %) and polystyrene (11.5 %) were the main plastic polymers. An estimated annual mean of 400 kg of plastics were moved by gulls into the lake. Only 1 % of plastic mass was imported in faeces.

DISCUSSION

Incorporating the biovectoring role of birds can provide a more holistic view of the plastic cycle and waste management. Biovectoring is predictable in sites worldwide where gulls and other waterbirds feed in landfills and roost in wetlands. We discuss bird deterrence and other ways of mitigating debris leakage into aquatic ecosystems.

Biovectoring of plastic by white storks from a landfill to a complex of salt ponds and marshes

Research into plastic pollution has extensively focused on abiotic vectors, overlooking transport by animals. Opportunistic birds, such as white storks (Ciconia ciconia) often forage on landfills, where plastic abounds. We assess plastic loading by ingestion and regurgitation of landfill plastic in Cadiz Bay, a major stopover area for migratory white storks in south-west Spain. On average, we counted 599 storks per day moving between a landfill and a complex of salt ponds and marshes, where they regurgitated pellets that each contained a mean of 0.47 g of plastic debris, dominated by polyethylene. Modelling reliant on GPS tracking estimated that 99 kg and >2 million particles of plastic were biovectored into the wetland during 2022, with seasonal peaks that followed migration patterns. GPS data enabled the correction of field censuses and the identification of plastic deposition hotspots. This study highlights the important role that biovectoring plays in plastic transport into coastal wetlands.

White stork movements reveal the ecological connectivity between landfills and different habitats

BACKGROUND

Connections between habitats are key to a full understanding of anthropic impacts on ecosystems. Freshwater habitats are especially biodiverse, yet depend on exchange with terrestrial habitats. White storks (Ciconia ciconia) are widespread opportunists that often forage in landfills and then visit wetlands, among other habitats. It is well known that white storks ingest contaminants at landfills (such as plastics and antibiotic resistant bacteria), which can be then deposited in other habitats through their faeces and regurgitated pellets.

METHODS

We characterized the role of white storks in habitat connectivity by analyzing GPS data from populations breeding in Germany and wintering from Spain to Morocco. We overlaid GPS tracks on a land-use surface to construct a spatially-explicit network in which nodes were sites, and links were direct flights. We then calculated centrality metrics, identified spatial modules, and quantified overall connections between habitat types. For regional networks in southern Spain and northern Morocco, we built Exponential Random Graph Models (ERGMs) to explain network topologies as a response to node habitat.

RESULTS

For Spain and Morocco combined, we built a directed spatial network with 114 nodes and 370 valued links. Landfills were the habitat type most connected to others, as measured by direct flights. The relevance of landfills was confirmed in both ERGMs, with significant positive effects of this habitat as a source of flights. In the ERGM for southern Spain, we found significant positive effects of rice fields and salines (solar saltworks) as sinks for flights. By contrast, in the ERGM for northern Morocco, we found a significant positive effect of marshes as a sink for flights.

CONCLUSIONS

These results illustrate how white storks connect landfills with terrestrial and aquatic habitats, some of which are managed for food production. We identified specific interconnected habitat patches across Spain and Morocco that could be used for further studies on biovectoring of pollutants, pathogens and other propagules.

Wing morphology covaries with migration distance in a highly aerial insectivorous songbird

According to classical prediction of aerodynamic theory, birds and other powered fliers that migrate over long distances should have longer and more pointed wings than those that migrate less. However, the association between wing morphology and migratory behavior can be masked by contrasting selective pressures related to foraging behavior, habitat selection and predator avoidance, possibly at the cost of lower flight energetic efficiency. We studied the handwing morphology of Eurasian barn swallows Hirundo rustica from four populations representing a migration distance gradient. This species is an aerial insectivore, so it flies extensively while foraging, and may migrate during the day using a ‘fly-and-forage’ migration strategy. Prolonged foraging flights may reinforce the effects of migration distance on flight morphology. We found that two wings’ aerodynamic properties – isometric handwing length and pointedness, both favoring energetically efficient flight, were more pronounced in barn swallows from populations undertaking longer seasonal migrations compared to less migratory populations. Our result contrast with two recent interspecific comparative studies that either reported no relationship or reported a negative relationship between pointedness and the degree of migratory behavior in hirundines. Our results may thus contribute to confirming the universality of the rule that longer migrations are associated with more pointed wings.

The Mitogenome Relationships and Phylogeography of Barn Swallows (Hirundo rustica)

The barn swallow (Hirundo rustica) poses a number of fascinating scientific questions, including the taxonomic status of postulated subspecies. Here we obtained and assessed the sequence variation of 411 complete mitogenomes, mainly from the European H. r. rustica, but other subspecies as well. In almost every case, we observed subspecies-specific haplogroups, which we employed together with estimated radiation times to postulate a model for the geographical and temporal worldwide spread of the species. The female barn swallow carrying the Hirundo rustica ancestral mitogenome left Africa (or its vicinity) around 280 thousand years ago (kya), and her descendants expanded first into Eurasia and then, at least 51 kya, into the Americas, from where a relatively recent (< 20 kya) back migration to Asia took place. The exception to the haplogroup subspecies specificity is represented by the sedentary Levantine H. r. transitiva that extensively shares haplogroup A with the migratory European H. r. rustica and, to a lesser extent, haplogroup B with the Egyptian H. r. savignii. Our data indicate that rustica and transitiva most likely derive from a sedentary Levantine population source that split at the end of the Younger Dryas (11.7 kya). Since then, however, transitiva received genetic inputs from and admixed with both the closely related rustica and the adjacent savignii. Demographic analyses confirm this species' strong link with climate fluctuations and human activities making it an excellent indicator for monitoring and assessing the impact of current global changes on wildlife.

Loss of largest and oldest individuals of the Montpellier snake correlates with recent warming in the southeastern Iberian Peninsula

The effects of climate change on organisms are now being extensively studied in many different taxa. However, the variation in body size, usually shrinkage in response to increasing temperature, has received little attention regarding to reptiles. During past periods of global warming, many organisms shrank in size, and current evidence and experiments manipulating temperature have shown a biomass decrease in some organisms with increasing temperatures. Here we test whether the body size of the Montpellier snake Malpolon monspessulanus from the southeastern Iberian Peninsula is changing and correlated with the increasing temperature in this region during a 39-year period (1976-2014). We measured the snout-vent length (SVL) of vouchers in scientific collections to check for trends in adult body size at the population level in relation with temperature, while controlling for the age of the individuals (estimated by skeletochronology, n =141). Given the great ontogenetic variation in body size of the study species, we categorized age in 3 classes: "young adults" (under 5 years old), "intermediate adults" (from 5 to 7 years old), and "old adults" (from 8 to 14 years old). By means of linear mixed models, we found a negative relationship between SVL of "old adults" and average annual temperature in the region during the lifetime of each individual. Our results indicate that largest and oldest individuals of the Montpellier Snake, that is, males because of strong sexual size dimorphism in this species, disappeared from the study population, and suggest that it occurred in response to rising environmental temperature.