Effects of a new waste collection policy on the population of yellow-legged gulls, Larus michahellis, in the historic centre of Venice (Italy)

Characterization of urban park litter pollution

Monitoring campaigns to collect and characterize urban park litter have been carried out in Italy annually from 2018 to 2023. A total of 274 urban parks in 108 cities (with 745 inhabitants to 2.7 million) were monitored. The citizen science approach was applied, and each campaign involved yearly an average of 416 volunteers coordinated by Legambiente. An adaptation of the sampling protocol proposed by the Marine Strategy Framework Directive (MSFD) Technical Group on Marine Litter (2008/56/CE) was applied. In total 161,293 (mean value 26,882.2 ± 4,743.4) items were collected within 42,300 m2 (density 3.82 items/m2). Cigarette butts are the most widespread waste: 36.3 % ± 5.5 % and up to 25 butts/m2 were found. Significant amounts of metal (16.2 %), glass/ceramics (13.0 %) and paper/cardboard (10.7 %) were found. Despite the COVID emergency having ended in 2021, during the 2022 monitoring campaign face masks only represent 0.2 % of the total waste items. No correlation was found between the amount of waste and the number of inhabitants or the geographical position of the city. The population density was poorly correlated with the quantity of waste collected while a slight correlation was evidenced by the presence of plastic bottles which seem to have decreased in recent years. Using the FTIR Spectroscopy 19 different polymers were identified. The most common were cellulose acetate (cigarette butts) polyethylene and polypropylene. Following the application of recent SUP regulations, polylactic acid and starch blended biopolymers were found (till 0.3 %). Finally, the presence of highly degraded polymers was observed.

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.

The abundance of yellow-legged gulls Larus michahellis breeding in the historic centre of Venice, Italy and the initial effects of the new waste collection policy on the population

The yellow-legged gull Larus michahellis has undergone widespread colonization of the urban environment in the recent past. The first urban breeding gulls were recorded in the historical centre of Venice, Italy, in 2000, and by 2005 there were already 24 roof-nesting pairs, with this number increasing significantly over the last decade. In 2016, a new door-to-door garbage collection system was introduced in Venice to prevent the accumulation of rubbish in the streets and limit the trophic resources available for the species. This study provides an up-to-date estimate of the Venice yellow-legged gull urban population using distance sampling method. We also studied the effect of the new waste collection system on the species by comparing the population estimate before (2017) and after (2018) the full implementation of this change and by analysing the trend of individuals collected in the old town by the wildlife recovery service during 2010-2018. Results estimated ca. 430 breeding pairs in June 2018 showing a 36% decrease with respect to 2017. We also found a decrease in the number of 1-year-old birds and pulli collected by the wildlife recovery service starting from 2016, when the policy implementation began. Our data did not show a significant decrease in the overall number of individuals, suggesting that the new policy has a stronger effect on the breeding success of the species than on adult survival. This study emphasizes the importance of preventing rubbish accumulation in the streets as factor for reducing the abundance of urban yellow-legged gulls.

Supplementary information

The online version contains supplementary material available at 10.1007/s11252-021-01175-7.