Background During recognition process, multiple parameters of the encountered stimulus may play a role. Previous studies with wild birds identified the importance of several salient features (e.g., eyes, beak, prominent elements of colouration) which birds use to recognise other bird species, such as predators or nest parasites. In the present study, we observed the responses of passerines visiting winter feeders to stimuli in the form of dummies of Eurasian sparrowhawk which were modified in body size and/or colouration but always carried the salient features of raptors (hooked beak, talons) and one species-specific feature of the sparrowhawk (yellow eyes). In the vicinity of a feeder, we placed a dummy of an unmodified sparrowhawk, life-sized sparrowhawk with pigeon, great tit, or robin colouration, a small, great tit-sized sparrowhawk dummy with unmodified or pigeon colouration, or an unmodified pigeon dummy, which functioned as a harmless control. Then we measured how it affected the number of visits. Results We found that birds were less afraid of small dummies regardless of their colouration than they were of life-sized raptor dummies or even the pigeon dummy. This contrasts with the results of a previous laboratory experiment where great tits’ reaction to small dummies was comparably fearful to their response to life-size dummies. In our experiment, birds were also not afraid of life-sized dummies with modified colouration except for a robin-coloured dummy, which caused an equally significant fear reaction as an unmodified sparrowhawk dummy. It is likely that this dummy resembled the colouration of a male sparrowhawk closely enough to cause this effect. Conclusions Based on our observations, we conclude that birds use contextual features to evaluate the size of other birds. Distance and familiar reference points seem to play an important part in this process.

In Europe, the common cuckoo (Cuculus canorus) is the most common and most studied brood parasite (Birkhead et al., 2011;Brooke & Davies, 1987;Esposito et al., 2022;Moksnes et al., 1991). The parasitic strategy of the cuckoo is very complex, with arms races developed with multiple host species. The parasitic event itself is very fast, cryptic, and planned in the period before incubation and after the first host eggs have been laid (Hamilton et al., 1965;Payne et al., 2005;Mann, 2017). The newly hatched cuckoo chick either

The important role of facial elements (hooked beak and conspicuous eye colour) in the recognition of avian predators has been repeatedly demonstrated. However, no attention has yet been paid to the importance of their canonical configuration i.e., the relative position of the eyes and beak. In our study, we tested the ability of untrained wild tits to recognise a dangerous predator (a sparrowhawk) with inverted eye and beak positions (invert dummy) and with one eye above and one below the beak (inline dummy) in aviary experiments. A dummy of a sparrowhawk with its head devoid of eyes and beak (empty dummy) served as a baseline alongside dummies of an unmodified sparrowhawk and a pigeon (as a harmless control). The experiment was carried out in two variants, with the complete dummy of the sparrowhawk visible and with the body of the dummy hidden in the bushes, from which only the head was visible. The tits showed no more fear towards the eyeless and beakless dummy than they did towards the pigeon. Towards the dummy with the modified configuration, the tits showed no less fear than towards the unmodified sparrowhawk, but in the case of the variant with an eye above and below the beak, their behaviour was different and can be interpreted as increased fear but also as surprise. Thus, the tits perceive a disturbance in the configuration of the predator faces, but do not show unambiguous signs of holistic processing i.e., impaired recognition of the inverted face.