AUDIBLE SCARING
Introduction
Some bird species transmit a ‘distress call’ when being attacked by a predator.
Some scaring systems play back recordings of these distress calls.
They should be played at their natural intensity: most of the gulls, the rook and starling are loud, the lapwing quiet. If played too loud, dispersal efficiency can decrease due to distortion.
At their natural sound level broadcast distress calls are not intrusive to people and often remain unnoticed.
Distress calls are not the same as alarm calls, which might be given on sighting a predator. These just alert birds rather than dispersing them.
Broadcasting distress calls elicits different reactions in different bird species. Gulls and corvids fly towards the sound to mob the predator. Smaller birds, such as starlings, will tend to stop and assess the situation, then disperse directly.
Distress call systems include the high quality Scarecrow Bio-Acoustic Systems devices such as the hand held Scarecrow Patrol, and the budget priced Bird Xpeller systems.
Starlings
The Scarecrow Patrol can be used, along with loud noises and bright lamps, to move starlings on from a roost.
All parts of the roost need to be within good earshot, so access equipment and/or multiple Patrols may be required.
Inform neighbours and police of the noise and duration in advance to prevent complaints and disruption.
As the birds start to arrive at the roost, start the disruption – make loud noises, play distress calls in 5-10 second bursts loudly towards where the birds are coming from, and shine bright lamps into the flock. As individual birds start to settle, use lamps to pick them out.
Continue until activity has stabilised for the night. This may take several hours. Each successive night there should be a reduced number that eventually roost. You might get a satisfactory result after one night, but it might take up to 5 to achieve all you can. The result is dependent on such factors as the number of birds, the scale of the scaring operation and the proximity of alternative roosting sites.
This method has a very good success rate, but some sites have proved intractable.
The starlings will often then stay away for the rest of the Winter, provided they are not moved on from their new roost. However, it may be necessary to repeat the disruption exercise, and it might also be necessary to repeat it the following year when the starlings return.
Bird Xpeller systems installed on farms in conjunction with dummy predator birds have been successful in deterring starlings from feeding on animal feedstuffs.
Gulls & Corvids
The typical technique for social and aggressive birds that communicate verbally within colonies, such as gulls and corvids, is to play the appropriate distress call for bursts of about 45 to 60 seconds. This allows the birds to hear the call, locate its direction, take to the air and fly towards the source to investigate, with the inherent intent of mobbing the predator. When they do not find a predator they are then unnerved by the possible danger and they disperse.
If the birds are being slow to react, try briefly waving a cloth (white for gulls, black for corvids) to simulate a struggling bird. If the birds are lingering in the air after the broadcast, another audible scaring device, such as a starter pistol or scaring cartridge, might hasten their departure. (NB To avoid confusing these species, these other audible scarers must not be used before or during the distress call broadcast, only after).
Dispersing birds from feeding sites such as landfills is more difficult: the playing time might need to be extended to give time for the birds to be dissuaded from feeding. Ideally commence the scaring operation prior to the arrival of birds to the feeding site. It is always more difficult to disperse birds that have already commenced feeding or roosting than to dissuade them from settling there in the first place.
Ultrasonics
In general, birds have similar hearing abilities to humans, so cannot hear ultrasonic sounds. Thus, ultrasonic sound generators have little or no effect in dispersing birds.
