Aerial “flycatching”: non-predatory birds can catch small birds in flight

Aerial flycatching — the lightning-fast seizure of flying small birds in the beak of larger, not normally predatory birds, only a few cases of which are treated in the literature — is here described and discussed for white storks (Ciconia ciconia) and crows (Corvidae).Communicated by F. Bairlein     

Gaze direction - a cue for hidden food in rooks (Corvus frugilegus)?

Other individual's head- and eye-directions can be used as social cues indicating the presence of important events. Among birds, ravens and rooks have been shown to co-orient with conspecifics and with humans by following their gaze direction into distant space and behind visual screens. Both species use screens to cache food in private; also, it had been suggested that they may rely on gaze cues to detect hidden food. However, in an object-choice task, ravens failed to do so, and their competitive lifestyle may have prevented them from relying on these cues. Here we tested closely related and cooperative rooks. Food was hidden in one of two cups and the experimenter gazed at the baited cup. In a second experiment, we aimed to increase the birds’ motivation to choose correctly by increasing the investment needed to obtain the reward. To do so, the birds had to pull on a string to obtain the cup. Here, the birds as a group tended to rely on gaze cues. In addition, individual birds quickly learned to use the cue in both experiments. Although rooks may not use gaze cues to find hidden food spontaneously, they may quickly learn to do so.     

No evidence of skewed secondary sex ratios in nestlings of the Common Raven (Corvus corax)

Many bird species adjust their offspring sex ratio as a response to environmental conditions or sexual dimorphism in size and dispersal. Offspring sex ratios may therefore vary among populations depending on the different demographic and ecological trajectories. We sampled Common Raven Corvus corax nestlings close to the fledging stage from three Central European regions to test for skewed secondary sex ratios and to investigate differences in sex ratios between populations that differ in recent recolonization history and breeding densities. Between 2005 and 2007, a total of 108 broods with 335 nestlings were sampled and their sex determined using molecular methods. We observed a mean of 3.1 (±1.2) nestlings per brood with no differences among nesting sites, years or regions. Nestling sex ratios were independent of the number of siblings. The overall secondary sex ratio was close to parity and did not differ between the variably structured populations.     

Haltung und Zucht der Java-Buschelster,Cissa thalassina (Temminck, 1826), im Cikananga Conservation Breeding Center (CCBC)

The Javan Green Magpie has just been upgraded to species level in 2011. Based on IUCN criteria, it has the global status “critically endangered”. As the captive breeding is an integral aspect for the survival of this species, it is kept and bred at Cikananga Conservation Breeding Center since 2011. Here, it was possible to observe new aspects of the breeding biology, such as behaviour and diet. The experiences about keeping and breeding this species shall be summarized and presented in this article.     

The performance of ravens on simple discrimination tasks: a preliminary study

Recent studies suggest the existence of primate-like cognitive abilities in corvids. Although the learning abilities of corvids in comparison to other species have been investigated before, little is known on how corvids perform on simple discrimination tasks if tested in experimental settings comparable to those that have been used for studying complex cognitive abilities. In this study, we tested a captive group of 12 ravens (Corvus corax) on four discrimination problems and their reversals. In contrast to other studies investigating learning abilities, our ravens were not food deprived and participation in experiments was voluntary. This preliminary study showed that all ravens successfully solved feature and position discriminations and several of the ravens could solve new tasks in a few trials, making very few mistakes.