A study of bird damage in a commercial orchard in the Auckland District : A thesis presented as a part requirement for the National Diploma in Horticulture

Abstract

Observations made in commercial apple orchards in the Auckland area , indicate that bird damage to fruit is a problem in most years. The extent of the problem has not been investigated, but casual observations the author made , while employed in the fruit - growing industry, indicated that birds may cause sufficient damage for the problem to be economically important. The later maturing apple varieties e . g . Golden Delicious and Giant Jeniton seem particularly prone to attack . The principal damage is caused by pecking of the fruits , but a proportion of the crop may be rejected for sale because of soiling by bird droppings. Damage commences at an early stage of maturation and continues until the fruit is harvested. During the maturation period , apple fruits go through several changes both internally and externally . The sugar level and flavour components increase while the acid level declines . Colour changes also occur. The background colour gradually changes from green to yellow as the fruit matures . Fruit enlargement continues with a resultant softening of the tissue . A rise in the respiration rate also occurs until it reaches its climacteric at fruit maturity. The incidence of bird damage may be linked to one or several of these changes . It has been suggested the presence of shelter belts in an orchard area , may influence the degree of damage caused by birds . Damage to other crops , such as peas , grain, sunflowers is usually more severe near shelter belts or fence lines. Observations suggest the birds use these belts as a source of cover, from which to carry out their attack. The problem of bird attack is probably of greater importance in those orchards where fruit is marketed through gate sales . This fruit is left on the tree to reach a later stage of maturity, than is fruit submitted to the New Zealand Apple and Pear Marketing Boar . Since more orchardists in the Auckland area are marketing their apple crop through gate sales, bird damage is, therefore, likely to become increasingly significant . It was decided, the problem of bird damage to apple crops bore investigation. It had been suggested that the rise in the percentage of soluble solids, and the decreaae of acidity in the maturing apple, might influence the amount of damage birds cause. It was decided to investigate the effect these changes have on bird depredation . As stated earlier, the presence of shelter belts in an orchard area is thought to influence the amount of damage birds cause. It was felt this aspect bore investigation also . It has been suggested (Dawson and Bull, 1970} that the most troublesome bird species in fruit crops are blackbirds (Turdus rnerula) , song thrushes (Turdus ericetorum), mynas (Aeridotheres tristis} , starlings (Sturnus vulgaris) , white-eyes (Zosterops lateralia) , and house sparrows(Passer domest1cus) . It was decided to carry out observations to determine the bird species resent in an orchard area , and which of those species were causing damage .