Nature vs. aviary: I have done these experiments both in nature using wild birds that can freely visit the experimental trees (Mäntylä et al. 2008a, 2010, 2014; Koski et al. 2015) and with birds that have been captured for a short time to observe their behaviour in an aviary or a booth (Mäntylä et al. 2004, 2008b + three experiments that will be published soon). I will tell more details about the experiments in nature in the next blog post, so here I will just mention that it is important to choose the study area so that there are plenty of insectivorous birds and preferably during the breeding season when they need plenty of insects for their offspring. You can increase the amount of birds with, for example, nest-boxes.
Species: Of course the bird species needs to be a species that eats insects, at least part of the year. In my experiments, I have used insectivorous birds, i.e. willow warblers (Phylloscopus trochilus: photo top left) and pied flycatchers (Ficedula hypoleuca; photo top right), and more omnivorous great tits (Parus major; photo bottom left and in the beginning of this post) and blue tits (Cyanistes caeruleus; photo bottom right) that eat insects especially during the breeding season. For an aviary experiment to be successful also statistically, at least 50 individuals are needed, preferably closer to 100. Remember when planning your experiment that around 5-10 % of the birds won’t behave as you expect they would. The study species needs to be common and/or easy to capture. Birds breeding in nest-boxes (such as pied flycatchers and tits) are easier to capture but I also managed to capture enough willow warblers with mist nets right after their breeding season.
Permits: I mentioned the need of permits and licences already in the two previous posts but here it is even more important. If you will capture a bird even for only fifteen minutes and nothing harmful happens, you will in any case need a licence for animal experiments from the official responsible for these in your country. Also, the researcher needs to have passed a course of animal experiments. There are several levels of these courses, so be careful when planning and sending the application. It is very useful to ring the birds tested in the experiments, so that one bird is not accidentally used several times. You will need a licence for ringing, too. And sometimes it can take a long time to get an answer from the officials. In my case, it took 6 months to get all the necessary licences from the officials in Berlin. And this was for experiments where great tits and blue tits where max one hour in captivity, and they were released back to nature unharmed.
Wild vs. captive: In my experiments I used birds caught from nature and returned there right after the short behavioural observations. Once I used pied flycatchers that were kept in captivity (Koski et al. 2015) and that was because the birds were there for another experiments (e.g. Ruuskanen & Laaksonen 2010) and there was no harm in doing this small extra experiment with them. Luisa Amo and her colleagues have done these tritrophic interactions experiments with captive great tits (Amo et al. 2013) and they showed that the captive birds won’t recognize the herbivore-damaged trees if they have never experienced those, but five hours of training was enough to teach this (Amo et al. 2016). This is one thing needs to be thought of if using captive birds. In nature birds have for sure seen or smelled plants with herbivorous insects and have learned to react to that but with birds reared in captivity that is not necessarily the case. So, the wild birds know what they should be looking for, but getting enough individuals can be difficult. Using captive birds could be easier (especially if they are in captivity anyway for other experiments) but their behaviour is not always natural.
Timing: I mentioned already that the best time to do the tritrophic experiment would be during the breeding season of the birds. But that is not always possible. In Berlin the officials were very strict with the animal experiment licences and I couldn’t capture the great and blue tits during their breeding season. Well, I did the experiments then in August-October and caught the birds from feeding places with mist nets. I got good results in my experiments but maybe they would have been even better during late spring and early summer. Sometimes you need to compromise and do the experiments at a time that is not optimal.
In the following posts of this blog I will go through more details how to do the experiments with the birds. If you have some comments on this post, please leave comments here.
© Elina Mäntylä (firstname.lastname@example.org), 21 June 2016