Introduced predators on islands are responsible for numerous native species extirpations and extinctions. Predation by cats is particularly detrimental to seabirds and cat control or eradication is generally the best option to reduce their negative impacts on native fauna. However, potential cascading effects, such as mesopredator release effect, need to be monitored after cat removal. In Port-Cros Island, a cat control campaign was undertaken to eliminate the strong and recurrent threat from feral cat predation to the small yelkouan shearwater Puffinus yelkouan population, without harming a neutered domestic cat population. To evaluate the conservation value of this campaign for an island endemic and endangered species, the diet and impact of the remaining domestic cats were studied through scat analysis and trap success. Moreover, to evaluate the recovery of the seabird population and detect any potential mesopredator release effect, shearwater and rat populations were monitored before, alongside and after the cat control. Only live traps were used, and most cats were trapped in the first year of cat eradication. The last incidence of cat predation on the yelkouan shearwater occurred the following year. The recovery of the shearwater population, occurring the first year of cat control, was mainly attributable to the settlement of new breeders in the colony. Rat population dynamics fluctuated widely but, even though the interactions between rats and shearwaters at breeding cavities increased, no evidence of rat predation on shearwaters was recorded. Thus, cat control on Port-Cros Island was a success for native species conservation, proving that such management strategy can induce an increase in the population of the endemic species, here the yelkouan shearwater, without any evidence of a mesopredator release effect.

The mechanisms by which introduced predators and long-lived seabirds interact and even coexist are still poorly known. Here, the interactions between the widely introduced black rat (Rattus rattus (L., 1758)) and an endemic Mediterranean cavity-nesting seabird, the yelkouan shearwater (Puffinus yelkouan (Acerbi, 1827)), were for the first time investigated for a set of 60 suitable breeding cavities throughout the entire breeding cycle of this seabird. Our results pointed out that rat visits to cavities were significantly higher when shearwaters had left the colony for their interbreeding exodus. Among the set of suitable breeding cavities, yelkouan shearwaters preferentially selected the deepest and the most winding cavities for breeding. Very few rat visits were recorded at the shearwater-occupied cavities and no predation event was recorded. These intriguing results reveal a low level of interaction between introduced black rats and yelkouan shearwaters, which may have facilitated their long-term coexistence for thousands of years on some Mediterranean islands.

Domestic cats (Felis catus) have been introduced on many islands in the world and are responsible for much damage to native insular faunas. The worldwide success and spread of this opportunistic predator is generally associated with its trophic adaptability. We examined the diet of a long-established feral cat population on a small Mediterranean island through the analysis of 1,219 scats collected during a 4-year period. Our results confirm that feral cats are generalist predators, able to feed on a wide range of prey. However, only a few prey species formed the major part of its diet. Two introduced mammals and a Mediterranean endemic seabird provided 93% of the yearly biomass consumed by cats (ship rats, 70%; wild rabbits, 7%; and yelkouan shearwaters, 6%). Ship rats remained by far the staple prey for cats throughout the year, but the diet of feral cats was more diversified in spring and early summer, frequently including insects, reptiles, and migrant birds. Endemic yelkouan shearwaters were preyed upon most frequently in autumn and winter, that is, during the shearwaters' prelaying period. Because rats provide the majority of the food of cats, they could help to maintain or inflate this alien predator population with deleterious consequences to the endemic shearwater. A cat eradication campaign would help protect the population of shearwaters on this island.

A comparative study was made of Yellow-legged Gull (Larus michahellis) chick diet at six colonies on rocky islands off the southeast coast of France, and which had marked differences in their accessibility to landfills. We determined the type of foraging habitat used (landfill, other terrestrial habitats, marine habitat) and the number of foraging habitats that supplied the food in each regurgitate (one, two or three). Landfills were consistently used by gulls from the six colonies, but not always as the main foraging habitat (38% to 83% of regurgitates). For the four colonies off Marseilles (high landfill accessibility), the majority of regurgitates contained food from only one foraging habitat while, at two colonies with low landfill accessibility, the majority of regurgitates each contained food obtained from two foraging habitats. Moreover, the Principal Component Analysis performed on diet features and landfill accessibility parameters demonstrate a significant inverse correlation between landfill accessibility and foraging on terrestrial habitats. The results underlined the influence of landfill accessibility on the characteristics of the chick’s diet. Moreover, they also suggest that during chick rearing, adult gulls shift their diet from a high specialization on landfill foraging (brooding period), towards a more diversified diet, feeding their chicks by increasing the use of terrestrial habitats..

We studied the diet of yellow-legged gulls, Larus (cachinnons) michahellis, at six colonies located at different distances from landfills during three breeding stages (territory establishment, pre-laying, and nesting periods) through the analysis of 1,192 pellets. Landfills were the foraging habitat most frequently used by gulls from all six colonies at all stages. Other terrestrial habitats were used with decreasing frequency as the breeding season advanced. Limited but consistent use was also made of the marine habitat. At each stage, landfill accessibility influenced the diet of the colonies, which showed both a varying degree of exploitation of landfills and a varying trophic niche width. We used principal components analysis (PCA) to assess diet variation patterns as the breeding season advanced as well as food accessibility parameters. The PCA revealed that gulls shift their diet toward a diet weakly diversified and increasingly centred on items from landfills and also showed that the diets of colonies were correlated with landfill accessibility and breeding stages. The shift in diet occurred earlier in the breeding season for colonies far from landfills compared to colonies near landfills. In light of these diet patterns, yellow-legged gulls appear to be strongly influenced by landfills; thus, the future closure of landfills is likely to have marked effects on yellow-legged gull population dynamics.

This study aims at determining breeding chronology and reproductive parameters (clutch-size, egg volume, hatching success and chick survival rates) in two Yellow-legged Gull Larus michahellis colonies showing a marked difference in anthropogenic food resources accessibility. For instance, one of the colonies studied, established on Ratonneau island, is very close to the large refuse dumps of Marseille city while the other, established on Bagaud island, is 30 km distant from the nearest refuse dump. The mean laying date of the first egg showed a significant difference between the two colonies. Although mean clutch-size does not significantly differ between the two colonies, complete 3-egg clutches were more frequent at Ratonneau. Mean egg volume was significantly different between the two colonies with a markedly smaller volume for the C-egg in the colony that was farther from human food sources. Moreover, hatching success and chick survival rates were significantly lower on Bagaud than on Ratonneau. All these differences may be linked to marked differences in resource accessibility, and in this way, anthropogenic food resources accessibility may be partly responsible for the clear difference in the demographic patterns of the two colonies for the last twenty years. These results could be used to calibrate more accurately certain demographic modelling in order to improve the population management of this superabundant bird species.