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A study of the food habits of the harrier hawk (Circus approximans gouldi Bonaparte) was made in the southern part of the South Island. Observations were made in the field and on two hawks kept in captivity, one an adult, the other a young bird. A quantitative-qualitative analysis was carried out on 129 crops and 129 stomachs between February 1966 and December 1967; during this time 254 food items were identified. The percentage occurrence of various groups of food items eaten between these dates are: traces of sheep 18.5%, small mammals 28.8%, passerines (including eggs and nestlings) 30.8%, ducks (grey and mallard) 5.0% and miscellaneous items 17.8%. Of the passerines 5.0% of their occurrence was either nestlings or traces of egg shell, the remaining 25.8% was adult birds. Eleven of the 13 duck food traces were found in hawks collected during the duck hunting season.

One interesting observation made during this research concerned sex determination. Some books have stated that eye colour can be used as a sex determinant for differentiating between adult males and adult females. However. after determining the sexes of these specimens by dissection and gonad inspection it was discovered that, of 29 females considered to be adults 18 had yellow irides, 7 had brown ones and 4 had occluded irides. In comparing some of the yellow irides of the adult females with some of those found in adult males no distinctive differences could be observed. The average weight of female hawks (juvenile and adult) was 822.5 grams with a variation from 622 to 1044 grams. The average male weight was 633 grams with variations from 392 to 725 grams. In captivity, an adult with an average weight of 722 grams consumed an average of 111.5 grams of food per day or 15.4% of its body weight. A young hawk was captured at 22 plus/minus 1 days of age. A food intake record was kept between days 24 and 55 and a weight record was kept between days 23 and 55. The average daily weight of the young hawk was 635 grams and it consumed an average of 128.8 grams of food per day between days 24 and 55. This is 20.3% of its body weight. Up to and including day 40 it consumed an average of 147.6 grams per day or 23% of its body weight while having an average weight of 635.4 grams. After day 40, a noticeable decrease in the average weight of food consumed was recorded. Between days 41 and 55 it consumed an average of 104.3 grams per day amounting to 16.4% of its average body weight of 635 grams.