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โครงการรวบรวมและจัดทําเอกสารวารสารอิเล็กทรอนิกส์ มหาวิทยาลัยเกษตรศาสตร์

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(Fallow & Magrath, 2010). As well as, distress calls that can communicate between mammal and bird
(Wise et al., 1999), or between species of birds (Marler, 2004). Pre-flight calls are a type of calls that
birds may use when they flee from predators, so it could transfer to species within a group of birds.
In bird species, interspecific signals need some similar structures that birds can decode between
species (Aubin, 1991). However, some species could respond to the calls of other species even

though they have different acoustic features (Curé et al., 2010).

Transferring information about predators could occur in sympatric species of birds. The
Common myna (Acridotheres tristis) and the White-vented myna (Acridotheres grandis) are sympatric
species that live in the same habitat in Thailand. They may use some signals to share information in
foraging and roosting time. Survival is important to mixed species of birds, so any signals that relate
to risk situations could be interspecific signals. Many researches have described interspecific signals

of distress and alarm calls, but have not considered pre-flight calls. Therefore, the vocal characteristic
of distress, alarm and pre-flight calls and the responses of mynas on these signals were investigated
in this study. This paper clarified interspecific communication in sympatric species of mynas in
Thailand. The research supports the use of bioacoustic stimuli that could elicit the responses of birds
in the mynas’ repellent project.

MATERIALS AND METHODS

Sound Recording and Sound Analysis

The data were collected between January-July 2017. Behavioural observations, sound
recordings and playback experiments were conducted between 6.00- 18.00 hr. The survey areas of
the Common myna (Acridotheres tristis) and the White-vented myna (Acridotheres grandis) were
around paddy fields and parks at Naresuan University and Chiang Mai province. Common myna and
White-vented myna were captured by using a mist net (mesh size 3x3 cm.), then distress calls were
recorded when a bird was held in hand. Pre-flight calls were recorded when the birds were released.

Otherwise, pre-flight calls were recorded when birds were fleeing from human presence. Alarm calls
were recorded when humans approached the birds or came near to their group members. Bird
sounds were analysed by using Raven Pro. V.1.5. Call structures of myna species were compared by
using t-test (Distress calls, n = 7; alarm calls, n = 10; pre-flight calls, n = 10). The structures of each
call composed of maximum frequency (kHz), minimum frequency (kHz), call length (second) and
bandwidth (kHz).

Experiments and Experimental Analysis

The best quality of the sound recordings were chosen for playback experiments. Distress, alarm
and pre-flight calls were recreated to be 1-minute in length. Distress, alarm and pre-flight calls of the
Common myna were 114, 60 and 118 elements respectively and White-vented myna were 92, 72
and 78 elements respectively. The stimuli were set at 80 dB, 5 seconds fade in and out with silent 5
seconds at the beginning of the sounds. Video camera (Sony Handicam, HDR-XR260) and Loudspeaker

วารสารสัตว์ป่าเมืองไทย ปีที่ 25 1 พ.ศ. 2561 Journal of Wildlife in Thailand Vol. 25, 2018