As Ultrasonic Sound falls in the range of 20khz -2Mhz, which is good for attracting Bats. Bird sounds are in the range of 20Hz -20Khz. Have you ever thought that actually you have been attracting lots of Bat all the while?
Someone calls me and asks should he use Ultrasonic sound as many of his friends encourage him to do so.
As we know Swiftlet hearing capability falls between the range of 20 Hz to 20 kHz, beyond this range they would not respond as this is beyond their hearing capability… but… there are still many do not understand this and relied heavily on Ultrasonic sound to attract Birds. Why hoping for something that is not realistic and impossible?
Below are the finding written by two renowned professors. For those still have high hope of Ultrasonic sound please read and may google what is ultrasonic sound.
"The frequency range of Swiftlet echolocating calls is between 1-6 kHz, with the most energy focused between 2-5 kHz (Fullard et al, . 1993). These frequencies fall into the range of normal human hearing. THERE IS NO ULTRASONIC COMPONENT (i.e., 20-160 kHz), which would be inaudible to the people. (Cranbrook & Medway, 1965)".
My opinion is similar to Cranbrook & Medway finding. Swiftlet farming is all about facts and experiment findings. All must be tested and proven with results.
Well after all have been said. It is up to you to decide anyway the Swiftlet farm belongs to you.
Some may even try to modify the Ultrasonic sound by changing some components and capacitors inside. Though it may attract some birds initially, but it is not long term. As changing some components and capacitors inside may alter the frequency and produces some different sound (weird sound). This defeated the sole purpose of the Ultrasonic sound. As a result, Bird is attracted to this weird sound as Swiftlets are very curious Birds. It won’t be long before they stop responding to it. So from not seeing any Bird before and now seeing some Birds making the owner overly excited thinking that the Ultrasonic sound modification works.
Note: This is my personal opinion. Others may think differently.
Good Swiftlet farming All!