Archiv pro měsíc: Květen 2017

Responses of urban crows to con- and hetero-specific alarm calls in predator and non-predator zoo enclosures

Publikováno | Autor:

2017

Kateřina Bílá, Jana Beránková, Petr Veselý, Thomas Bugnyar, Christine Schwab

DOI: 10.1007/s10071-016-1047-5

Abstrakt:

Urban animals and birds in particular are able to cope with diverse novel threats in a city environment such as avoiding novel, unfamiliar predators. Predator avoidance often includes alarm signals that can be used also by hetero-specifics, which is mainly the case in mixed-species flocks. It can also occur when species do not form flocks but co-occur together. In this study we tested whether urban crows use alarm calls of conspecifics and hetero-specifics (jackdaws, Corvus monedula) differently in a predator and a non-predator context with partly novel and unfamiliar zoo animal species. Birds were tested at the Tiergarten Schönbrunn in the city of Vienna by playing back con- and hetero-specific alarm calls and control stimuli (great tit song and no stimuli) at predator (wolf, polar bear) and non-predator (eland antelope and cranes, peccaries) enclosures. We recorded responses of crows as the percentage of birds flying away after hearing the playback (out of those present before the playback) and as the number of vocalizations given by the present birds. A significantly higher percentage of crows flew away after hearing either con- or hetero-specific alarm calls, but it did not significantly differ between the predator and the non-predator context. Crows treated jackdaw calls just as crow calls, indicating that they make proper use of hetero-specific alarm calls. Responding similarly in both contexts may suggest that the crows were uncertain about the threat a particular zoo animal represents and were generally cautious. In the predator context, however, a high percentage of crows also flew away upon hearing the great tit control song which suggests that they may still evaluate those species which occasionally killed crows as more dangerous and respond to any conspicuous sound.

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Visual warning signals of the ladybird Harmonia axyridis: the avian predators’ point of view

Publikováno | Autor:

2014

Alexandra Průchová, Oldřich Nedvěd, Petr Veselý, Bára Ernestová, Roman Fuchs

DOI: 10.1111/eea.12176

Abstrakt: Previous studies have suggested that spotted patterns are important in the protection of ladybirds against attack by avian predators. Nevertheless, these studies were based on the comparison of several ladybird species differing in colouration, but also in other traits (e.g., chemical protection). We presented natural as well as artificial colour modifications (using brown, red, and black paint) of the ladybird Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) – an invasive alien species for Europe – to an avian predator, the great tit, Parus major L. (Passeriformes: Paridae). All forms were considered to be equal in size, but differed in colouration and in the presence of spots. The chemical protection was equal except for one form. The birds displayed strong avoidance of all forms with red and black colouration; beetles with artificially removed red colouration (painted brown) were attacked more often. The beetles painted brown with black spots were slightly better protected than the painted beetles without spots. We can sum up that spots are of some importance in the protection of ladybirds; nevertheless, red and black colouration is the main part of the visual signal.

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Importance of conspicuous colours in warning signals: the great tit’s (Parus major) point of view

Publikováno | Autor:

2014

Alena Cibulková, Petr Veselý, Roman Fuchs

DOI: 10.1007/s10682-014-9690-2

Abstrakt: Few studies have dealt with the importance of colours per se in warning signalling, with the use of a broader array of different colours. We tested the reactions of great tits (Parus major) to colour modifications (red, orange, yellow, white, blue, violet, and green) of the warning signal of the red firebug (Pyrrhocoris apterus), preserving its typical black pattern. We used the edible Guyana spotted roach (Blaptica dubia) as the prey, each of which carried a paper sticker shield of a particular colour on its back. With such prey, the effects of the other traits of the red firebug (e.g. shape of the legs and antennae or chemical signals) on the birds’ reactions were removed. All of the conspicuous forms of the prey, possessing a black pattern, were protected against great tits better than the non-patterned brown control form. The level of protection decreased from those forms with colours similar to the model and commonly occurring in warning signals in nature (red, orange, yellow), through other conspicuous colours rarely occurring in warning signals in nature (white, violet, blue), to the colour which usually occurs as cryptic in nature (green). In the green form, repeated encounters were necessary to reach avoidance. Avoidance learning came to pass despite the fact that the presented prey was neither inedible nor distasteful.

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Do predator energy demands or previous exposure influence protection by aposematic coloration of prey?

Publikováno | Autor:

2017

Petr Veselý, Barbora Ernestová, Oldřich Nedvěd, Roman Fuchs

DOI: 10.1093/cz/zow057

Dravci se snaží ulovit kořist a kořist by se zase moc ráda tomuto osudu vyhnula. Živočichové, kteří v přírodě hrají roli kořisti, mají k dispozici různé triky, s jejichž pomocí zvyšují své šance. Jedním z nich je i výstražné zbarvení. Nejde o žádné maskování. Potenciální kořist se naopak velice snaží, aby o sobě dala dravci vědět a upozornila ho na to, že je nechutná, nepoživatelná nebo dokonce jedovatá. Takové zbarvení se vyskytuje hlavně u hmyzu, a pak také u žab, plazů, ryb a dalších živočichů.
Čtěte více na webu PřF JU.

Anglický abstrakt:

Growing evidence exists that aposematic and toxic prey may be included in a predator’s diet when the predator experiences physiological stress. The tree sparrow Passer montanus is known to have a significant portion of aposematic and toxic ladybirds in its natural diet. Here, we present experiments testing the attack and eating rate of the tree sparrow toward the invasive aposematic harlequin ladybird Harmonia axyridis. We wondered whether the sparrow’s ability to prey on native ladybirds predisposes them to also prey on harlequin ladybirds. We compared the attack and eating rates of tree sparrows of particular age and/or experience classes to test for any changes during ontogeny (hand-reared × young wild-caught ×adult wild-caught) and with differing perceived levels of physiological stress (summer adult × winter adult). Winter adult tree sparrows commonly attacked and ate the offered ladybirds with no evidence of disgust or metabolic difficulties after ingestion. Naïve and wild immature tree sparrows attacked the ladybirds but hesitated to eat them. Adult tree sparrows caught in the summer avoided attacking the ladybirds. These results suggest that tree sparrows are able to cope with chemicals ingested along with the ladybirds. This pre-adaptation enables them to include ladybirds in their diet; though they commonly do this only in times of shortage in insect availability (winter). Young sparrows showed avoidance toward the chemical protection of the ladybirds.

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