Heterospecific nest material kleptoparasitism: observations of grey herons, Ardea cinerea, removing material from the nests of monk parakeets, Myiopsitta monachus

Nest material kleptoparasitism occurs when an individual steals material from another individual's nest. Here we document 69 observations of grey herons, Ardea cinerea, removing nest material from the nests of monk parakeets, Myiopsitta monachus. The observations coincided with the breeding season of grey herons in Barcelona. We observed the behaviour by multiple individuals, across two years, at multiple nests in four different monk parakeet nesting trees, suggesting that theft of nesting material by grey herons is prevalent in this population. The large nests of the monk parakeet may present a rich source of nesting material that is less costly to collect than gathering nest material elsewhere. Our observations add to the relatively limited number of reports of nest material kleptoparasitism in wild birds and especially between heterospecifics.