Video recordings and ethological analysis of behavioural
categories
During acoustic-visual recordings, a second hydrophone (HTI-96-Min, High
Tech Inc., Long Beach, MS, USA, sensitivity: -201 dB re. 1V
µPa-1, frequency response 2 Hz to 30 kHz), placed less
than three cm from the nest opening, was connected directly to a video
camcorder (Canon Legria FS200, 41x digital zoom, 25 frames/sec, Tokyo,
Japan) to directly synchronise acoustic and visual signals into a
uniform dataset (.mod format) for subsequent analysis. By including or
excluding different females into a male’s territory, we could control
the experimental variables of interest under standardised conditions and
study multimodal communication in males. The camcorder was mounted on a
stand and positioned approx. 40 cm from the front of the experimental
glass tanks. Quantitative ethological analysis of the courtship,
pre-spawning and spawning phases was performed by calculating the number
of sounds co-occurring with each behavioural category. Courtship
behaviour began when the females entered the male territory at a
distance of <5 cm from the male’s nest, while the pre-spawning
phase was observed when the ripe female entered the male’s nest.
Spawning was observed beginning with the female turning upside-down in
the nest numerous times in short succession (assumingoviposition ) and started circling the ceiling. Male behaviours
and the associated sound emissions were observed in four soniferous
males during seven recording sessions and analysed using Solomon Coder
(ver. beta 19.08.02). Again, the ripe females were chosen for the
recording sessions according to two indicators of their readiness for
spawning (belly and eye coloration). Behavioural categories (and
behavioural acts per category) expressed by the males were classified
and scored according to our observations and the literature (Amorim &
Neves, 2007, 2008; Amorim et al., 2013; Malavasi et al., 2009). In
Solomon Coder, two datasets were analysed separately and then compared.
Firstly, behavioural coding was performed by re-watching the video
recordings with sound production involving five females (N = 5; 37.23 ±
4.29 mm LS; range: 31.62 – 43.76 mm) and documenting
the frequency (n min-1) and duration (in sec)
of behavioural categories, calculating their total occurrence and
percentage. In addition, we analysed eight video recordings (two per
male) containing the behaviours of the same four tested males, but
performed with six different females (N = 6; 37.23 ± 4.29; range: 31.62
– 43.76 mm) when they did not co-occur with sound production
(i.e., males were mute for the entire recording period). By
having these two datasets, we investigated the differences in
frequencies of behavioural categories in males when they engaged in
sound production and when they did not. In total, we used a total of
eight males in our experiments, but four were unresponsive (i.e. ,
did not perform courtship behaviour or sounds), resulting in
insufficient data for their further analyses. We analysed videos using
Solomon Coder for the following behavioural parameters: male behaviour
rate (the total number of behavioural acts per min) (1) co-occurring
with sounds or (2) not co-occurring with sounds; number of times a
female entered the male’s nest accompanied with sounds (3) or (4)
without sounds; (5) total behaviours (number of behavioural categories
per video recording).