CASE STUDY: Green Island Foundation

"We use a ground-based speaker array from Scarecrow to attract the birds. Speakers were placed on the ‘nesting’ site itself with another set on the roof of the abandoned building playing audio of a thriving sooty tern colony.”

Wilna Accouche, The Green Island Foundation


The re-establishment of a sooty tern colony on Denis Island in the Seychelles is a fascinating example of how sophisticated bio-acoustic bird deterrent technology can be used to attract birds and benefit the overall wellbeing and protection of a species.



The situation

Scarecrow products are usually deployed to deter birds and keep them away from a site, but our extensive library of bird calls and expert approach can also be easily used to attract them.

This has been necessary for one client on the exotic Denis Island in the Seychelles; Denis is in the north of the island group and is known for its pristine white sand beaches and sea turtle sanctuary. It is also a haven for countless sea birds.

Scarecrow first started working with the Green Island Foundation (GIF), an environmental NGO, in 2007 after years trying to re-establish a sooty tern colony. It had always had a thriving community of terns and while not an endangered species, their colonies are strictly protected across the globe.

The sooty tern is a common seabird found in the Seychelles, however its nesting colonies have been under increasing threat. The colony on the island had been severely impacted over the years by a combination of human encroachment, natural predation and egg theft. Particularly, the introduction of cats, rats and myna birds over the years were identified as key causes of the decline. This resulted in several colonies on the island going extinct.

GIF had been trying to re-establish the colony using a variety of techniques to entice the birds but despite using decoy birds and clearing vegetation to make the colony space more attractive to the terns, nothing had been effective.

Scarecrow was brought in to deploy its bio-acoustic technology and auditory bird call emitting equipment to entice the birds to nest.


The solution 

The result of using Scarecrow equipment and expertise has been dramatic and Denis Island now has a thriving sooty tern colony. GIF has so far purchased five Scarecrow B.I.R.DTM System  and two Scarecrow 360TM Systems, working closely with the team over a 16-year relationship.

Each year, in preparation for the coming breeding season, a site at the southern point of the island is cleared of vegetation, creating the ideal space that the birds need to feel safe from predators. Sooty terns naturally breed in large colonies, so the challenge was to create the impression of lots of birds already using the site, both visually and audibly.

Each year, the GIF team deploy both a range of two-dimensional and three-dimensional model birds that indicate to the terns flying overhead that the area is populated and safe. The decoys are carefully placed in a loose circle group with pairs facing each other as if they are courting and the vegetation is cut back and continually pruned several times during the breeding season.

A Scarecrow 360TM system is installed at ground level and audio equipment is hidden in the grasses. At set intervals it plays out the background of a thriving sooty tern colony, which has effectively enticed the birds to quickly feel confident to land, join an established colony and start nesting. Seawater was also occasionally poured onto the site to cause the vegetation to wilt, to simulate a natural effect of a large bird colony.

The colony background sounds had been previously generated by recording an established sooty tern colony on the neighbouring Bird Island. Great care was taken over making the recordings, to ensure it was of the birds at their most relaxed and natural. Sounds were obtained at the edge of the breeding area on the Bird Island colony, around two metres from the nearest birds.

Recording only began once birds had accepted the presence of the equipment and sound recordist and stopped reacting. Timing the recordings was also key. Recordings were made during the day, when the colony was at its most active, and also four hours after dark, at 10pm, when the colony remains noisy but less so than during daytime.

Originally, speaker arrays were carefully placed on the nesting site to offer effective sound coverage but not to be intrusive. One set was placed at ground level, hidden in vegetation and another set on the roof of an adjacent abandoned building [pictured].

Scarecrow supplied an airfield bird scaring unit, which is fitted with a light sensor that switches between day and night recordings. The bird calls were broadcast through four Scarecrow 1215/L 20w re-entrant horn loudspeakers, each connected to the control unit by armoured cable. The unit was powered by a 12V car battery that was recharged from a solar panel.


The results

This on-going project has resulted in Sooty Terns now continuously inhabiting Denis Island during the nesting season, which coincides with the southeast monsoon. Project co-ordinators are hoping that the birds will eventually breed on the island.


Scarecrow Technology

Bio-acoustics science is the combination of biology and acoustics. Scarecrow develops and uses digital technology, including equipment and software, to record, analyse and broadcast the natural sounds of birds for their safe and humane dispersal around the world. Contact the Scarecrow team and find out how we can help.