Nesting innovations allow population growth in an invasive population of rose-ringed parakeets

Certain traits of recipient environments, such as the availability of limiting resources, strongly determine the establishment success and spread of non-native species. These limitations may be overcome through behavioral plasticity, allowing them to exploit alternative resources. Here, we show how a secondary cavity nester bird, the rose-ringed parakeet Psittacula krameri, innovates its nesting behavior as a response to the shortage of tree cavities for nesting in its invasive range in Tenerife (Canary Islands). We observed that some breeding pairs excavated their own nest cavities in palms, thus becoming primary cavity nester, whereas others occupied nests built with wood sticks by another invasive species, the monk parakeet Myiopsitta monachus. The use of these novel nesting strategies increased the number of breeding pairs by up to 52% over 6 years, contributing to a 128.8% increase of the whole population. Innovative nests were located at greater heights above ground and were more aggregated around conspecifics but did not result in greater breeding success than natural cavities. Occupation of monk parakeet colonies by rose-ringed parakeets also benefited the former species through a protective-nesting association against nest predators. Our results show how an invasive species innovate nesting behaviors and increase nest-site availability in the recipient environment, thus facilitating its population growth and invasion process. Potential behavioral innovations in other invasive rose-ringed parakeet populations may be overlooked, and should be considered for effective management plans.

Long-eared Owl Asio otus breeding in a Caspian Gull Larus cachinnans colony: Reversed roles in protective nesting association?

We describe the event of Long-eared Owls Asio otus nesting on an island within a colony of Caspian Gulls Larus cachinnans at the Mietków Reservoir (SW Poland). The owls nested in an old (possible corvid) nest in a willow and raised two owlets. They probably did not hunt gulls, neither adults nor chicks. We suggest that, in this case, the Long-eared Owls benefitted from breeding within a gull colony because of the added security against predators that the gulls provided.

Nest association between two predators as a behavioral response to the low density of rodents

Many birds nest in association with aggressive birds of other species to benefit from their protection against predators. We hypothesized that the protective effect also could extend to foraging resources, whereby the resultant resource-enriched habitats near a nest of aggressive raptors could be an alternative cause of associations between nesting bird species with non-overlapping foraging niches. In the Arctic, the Rough-legged Hawk (Buteo lagopus) and the Peregrine Falcon (Falco peregrinus) are 2 raptor species with non-overlapping food resources that have been reported to nest sometimes in close proximity. Since nesting Peregrine Falcons are very aggressive, they may protect the small rodent prey near their nests from predation, and Rough-legged Hawks could use these hot spots as a nesting territory. In 2 regions in low Arctic Russia we found that (1) the nesting territories of Peregrine Falcons were indeed enriched with small rodents as compared to control areas, (2) the probability of nest association between the 2 raptors increased when rodent abundance was generally low in the region where hawks did not use alternative prey, and (3) hawk reproductive success increased when nesting close to Peregrine Falcons. These results suggest that implications of aggressive nest site defense in birds in certain cases may involve more mechanisms than previously explored. A key ecological process in tundra, rodent population cycles, may explain the occurrence and adaptive significance of a specific behavior pattern, the nesting association between 2 raptor species.

Observation of an Unusual Nesting Association between Spanish Sparrows Passer hispaniolensis and Lesser Grey Shrikes Lanius minor

We report a case of unusual mixed nesting association of several pairs of Spanish Sparrows Passer hispaniolensis and one pair of Lesser Grey Shrikes Lanius minor near Pepelište village (41° 31′ 11″ N, 22° 7′ 41.43″ E), central Macedonia. All nests were built near the trunk of a Black Locust Robinia pseudoacacia at a height of ca. 8 m. Although the nests of both species were in close proximity, we observed no interspecific aggression. Such a mixed colony could be advantageous for both species in a locality with abundant nest predators.