Red-backed shrikes (Lanius collurio) behave quite differently towards two common nest predators. While the European jay (Garrulus glandarius) is commonly attacked, in the presence of the Eurasian magpie (Pica pica), shrikes stay fully passive. We tested the hypotheses that this passive response to the magpie is an alternative defense strategy. Nesting shrikes were exposed to the commonly attacked European kestrel (Falco tinnunculus) in a situation in which i) a harmless domestic pigeon, ii) a commonly attacked European jay, and iii) a non-attacked black-billed magpie are (separately) presented nearby. The kestrel dummy presented together with the magpie dummy was attacked with a significantly lower intensity than when it was presented with the other intruders (pigeon, jay) or alone. This means that the presence of the magpie inhibited the shrike’s defense response towards the other intruder. These results support our previous hypotheses that shrikes use an alternative defense strategy in the magpie’s presence. We hypothesize that the magpie is able to associate the active defense of the shrikes with the close proximity of a nest and that shrikes try not to draw the magpie’s attention to the nest. The reason why this strategy is not used against the jay remains unanswered as jays as well as magpies show very similar cognitive and foraging skills enabling them to individuate the nest presence according to active parental defense.
Aposematism is a special part of communication between predator and its prey. It combines conspicuous coloration with noxiousness (in many cases with unpalatability). Function of aposematism is to protect the prey against predator. Aposematism results in predator`s association of noxiousness with the colour pattern and therefore next avoiding the aposematic form of the prey in the future. Avoiding aposematic prey could be innate or learned through the life. This kind of protectivity is present in many species of animals. Studying of the response of the predator to such an aposematic prey is the aim of my master thesis.
The experimental apparatus is a special cage. Its front wall is made of one-side transparent mirror in order not to disturbe behaviour of the processed bird by the presence of experimentator. Experimental prey is presented to the bird on a revolving feeder tray and behaviour of the bird is noted by programme Observer, ver. 5.0, for 5 minutes per one item of prey. This programme is usually used for collecting ethological data. Each bird is offered 10 items of prey (one for each trial) – alternating one maggot and one bug, it means 5 maggots and 5 bugs of the same colour form totally. Maggots are presented to prove that the bird is starving and to be sure that avoiding experimental prey is due to its aposematism. Repeating of the trial can reveal us individual learning of the bird through the whole experiment.
Through the experiment, different types of predator’s behaviour are distinguished – exploring, searching, approaching, handling prey, feeding prey, vomiting, resting, drinking and cleaning the bill. Presence, frequency and total duration of different types of behaviour is noted in each trial. Species of bird, its age and sex, period of year, colour of bug and order of trial in frame of the experiment will be explanatory variables in the statistical analysis. Nowadays I’m at the end of the first part of my thesis (collecting enough data). The second part (statistical analysis) is still to come.
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