The topic of this post is to describe what kind of aviaries or booths I have used when doing behavioural experiments with birds. I concentrate on experiments where the bird can make a choice between two branches, one from an herbivore-damaged tree and one from an intact control tree. More specifically they were branches with only systemically herbivore-induced defence, so the branches used in the bird experiments hadn’t had any caterpillars (see photos in my previous posts; plants and insects).
Size and shape: A Y-shaped aviary would be the best shape when doing choice experiments (as in Amo et al. 2013, 2016). But that is not always possible. I have done my bird choice experiments in smallish booths, mainly because of lack of space. For the experiment with willow warblers (Phylloscopus trochilus; Mäntylä et al. 2004) I used a booth already available at the Kevo Subarctic Research Institute (photo on the left). Its measures were height 97 cm, depth 118 cm, width 75 cm. In my experiments with great tits (Parus major) and blue tits (Cyanistes caeruleus) the measures of the booth were height 176 cm, depth 116 cm, width 116 cm in Turku (photo on the right; Mäntylä et al. 2008b) and height 170 cm, depth 100 cm, width 100 cm in Berlin (photo on the top of this post; articles published soon). The booths may seem small but they were big enough to fit the two branches so that they were not touching each other, and also for following the behaviour of the birds for 10-15 minutes.
Material: In my experiments I tried to design the experimental booths so that there is no other place for the birds to sit than the two experimental branches (and of course the floor). Therefore, the material for the surfaces was smooth plywood. This of course didn’t mean that the birds wouldn’t find some places to hang on or sit. 😉 But I did my best to make the data collection and interpretation as simple as possible. The smooth surface is also easy to clean after each bird. In the above photo on the right you can see that for some reason I took this photo before cleaning the booth for the next bird. 😉
Lighting: Of course it would be best to use natural sunlight (as in Amo et al. 2013, 2016) but with that can come some problems. There could be differences between study days in temperature, wind and rain. Also sounds and smells of the surroundings could have an effect on the behaviour of the bird. I did my experiments in closed booths, so I needed light that was as natural as possible. In all the experiments I used lights from True-Light. They include also UV wavelengths and are non-flickering. Those are both important qualities since diurnal birds can see UV (e.g. Lind et al. 2014) and distinguish flickering even up to 140 Hz (Boström et al 2016) compared to 50-100 Hz in humans. And if possible the light source should be in the centre of the ceiling, so that there is no difference in lighting between the left and right side of the booth.
Door: I needed to recapture the birds from the booth after the experiment to measure and ring them before release back to nature. Therefore, I needed a door to enter the booth. So, the front wall was also a door. A small window (10 cm × 10 cm) in the door is useful because then you can check where the bird is before entering. And the window is also useful just in case something unexpected happens during the observation. The door needs to open smoothly and close tightly so that the bird won’t try to escape from the corners.
Video: In my first study of this topic I didn’t have a video camera. I watched the birds through the small window and wrote down the time when they changed location (either branch or elsewhere in the booth). But in my later experiments I’ve used a video camera and that is much better. You get more detailed data that way. In my set-ups I’ve installed the video camera to film through a small hole in the ceiling (see photo on the top of this post). Remember to put a plate of glass or transparent thick plastic between the hole and the camera lens. The birds are sometimes very curious about the camera (see photos below). 😉
© Elina Mäntylä (firstname.lastname@example.org), 6 July 2016