While chestnuts grow inside a spiky burr, these burrs are no match for the hard, hacking beaks / bills of sulphur crested cockatoos. However, your ‘Balloon Hawk Bird Scarer’ is without doubt, the most effective & environmentally friendly solution we’ve found to control cockies! Cockies expect to see hawks above them, so as they start to fly in the direction of our trees, a quick look up is all it takes for them to see the replica hawk and be frightened into changing their flight path before they reach our trees. It all works a treat and significantly reduces our reliance on a gas gun, it’s a very cost effective solution! Great product guys!