September | 2018 | CENTRE OF COGNITIVE ETHOLOGY

2018

Abstract:

Heterospecific alarm calls are typically found in situations where multiple species
have a common predator. In birds, they are particularly common in mixed mixed-species flocks. In species with highly developed social and cognitive abilities like corvids, there is the potential for differential responses to heterospecific vs. conspecific
calls according to the riskiness of the habitat. We tested the responses of free-ranging
ravens (Corvus corax) to conspecific alarm calls and compared them to heterospecific
alarm calls of jackdaws (Corvus monedula). We observed the proportion of ravens leaving the feeding site after the con-or hetero-specific playback was presented in a situation of low threat (wild boar—Sus scrofa enclosure) and high threat of
predation (wolf—Canis lupus enclosure). We show that ravens responded to conspecific calls more intensively at the wolves than at the wild boar, but the response to conspecific calls was in both enclosures stronger than to the control (great tit—Parus
major song). The response to the heterospecific alarm was also stronger in the wolves’
enclosure, but it did not differ from control in the wild boar enclosure. These findings
suggest that ravens are aware of the meaning of the jackdaw alarm calls, but they
respond to it only in a situation of high predatory threat (wolves are present). In the
wild boar enclosure, the ravens probably consider jackdaws warning against some
other predator, very probably harmless to ravens. This interpretation requires further
testing, as both enclosures differ also in respect to other parameters like food quality
and shelter availability.

2018

Piotr Ceryngier, Oldřich Nedveěd, Audrey A. Grez, Eric W. Riddick, Helen E. Roy, Gilles San Martin, Tove Steenberg, Petr Veselý, Tania Zaviezo, Álvaro Zúniga-Reinoso, Danny Haelewaters

DOI: 10.1007/s10530-017-1608-9

Abstract:

The harlequin ladybird Harmonia axyridis (Coleoptera: Coccinellidae) has rapidly spread in several continents over the past 30 years and is considered an invasive alien species. The success of H. axyridis as an invader is often attributed to weak control by natural enemies. In this paper, we provide an overview of current knowledge on predators and parasitoids of H. axyridis. The common feature of predators and parasitoids is that they directly kill exploited organisms. Currently available data show
that H. axyridis, displaying a variety of chemical, mechanical, and microbiological anti-predator defenses, is usually avoided by predators. However, some birds and invertebrates can eat this ladybird without harmful consequences. The primary defenses of H. axyridis against parasitoids include immune response and physiological and nutritional unsuitability for parasitoid development. These defenses are probably relatively efficient against most ladybird parasitoids, but not against flies of the genus Phalacrotophora. The latter are idiobiont parasitoids and hence can evade the host’s immune response. Indeed, rates of parasitism of H. axyridis by Phalacrotophora
in the Palaearctic region (both in the native range in Asia and in Europe) are relatively high. While strong evidence for enemy release on the invasive populations of H. axyridis is lacking, several cases of parasitoid acquisition have been recorded in
Europe, North America, and South America. We conclude that enemy release cannot be excluded as a possible mechanism contributing to the spread and increase of H. axyridis in the early stages of invasion, but adaptation of parasitoids may lead to novel
associations which might offset previous effects of enemy release. However, further work is required to elucidate the population-level effects of such interactions.