The Kakapo (Strigops habroptilus) is a unique New Zealand parrot that is threatened with extinction. It is large, flightless, and nocturnal. The breeding biology of the Kakapo is characterized by a lek mating system with all parental care of the eggs and young performed by the female, and by the occurrence of egg laying and successful breeding at intervals of several years. The Kakapo became extinct on the mainland in the early 1980s, at which time there was still a natural population of about 60 birds on Stewart Island. Today, the remaining population (ca. 33 males and 17 females) consists entirely of birds moved to other islands off the New Zealand coast. There are very few female Kakapo remaining, and it is clearly important for the conservation of the species to maximize the breeding output of every female. A management strategy to achieve this is dependent on knowledge of the activity of the reproductive system of female Kakapo during potential breeding seasons. However, though male Kakapo show very obvious sexual behavior (booming), the only direct measure of female reproductive activity is evidence of mating at booming bowls (i.e. feathers pressed into the ground; Powlesland et al. 1992), and the discovery of nests with eggs. Measures of this type provide no information about changes in ovarian size in birds that do not lay eggs. Plasma hormone levels can be used to assess ovarian activity in birds, but it is not practical to collect blood samples from free-living Kakapo. The need for information on ovarian activity in Kakapo led us to consider an alternative, non-invasive approach. Steroid hormone levels can be measured in avian droppings (Bishop and Hall 1991), and Kakapo produce droppings that can be collected from the forest floor. These droppings are larger than those worked with by Bishop and Hall (1991), so we applied recently developed methods for measuring testosterone and estradiol levels in chicken droppings (Cockrem and Rounce 1994) to an analysis of Kakapo droppings. Droppings were collected for 16 months in order to determine the annual pattern of steroid levels and to relate this pattern to the events of the breeding cycle. Kakapo droppings were collected from the forest floor on Little Barrier Island, New Zealand, by Department of Conservation staff. Droppings were collected from tracks during routine operations each day, returned to the field base, and frozen in liquid nitrogen or at -20?C. They were later transported to the laboratory for analysis. Collections generally, but not alwavs, were made daily; therefore, the length of time between a dropping being produced by a bird and collection of the dropping varied from less than a day to several days. The droppings were subjected to natural, field weather conditions before collection. Droppings were available for hormone assay for the months of September 1989 through December 1990, except that there were no samples from December 1989 or January 1990. The sample size was usually four or five droppings per month (major exceptions being one dropping in September 1989 and 24 in March 1990). Three of the droppings were collected from birds of known sex during a handling procedure. The identities of the birds that produced the other dropping were unknown, and more than one dropping in each month's sample could have come from a given bird. The procedure for preparation of the fecal samples followed Cockrem and Rounce (1994). It was based on Bishop and Hall (1991) and consisted of the mixing of dried fecal samples with a phosphate buffer solution. This mixture was soaked overnight and then centrifuged, with aliquots of the buffer extract subsequently taken for hormone assay. Frozen droppings were thawed, thoroughly stirred, and then dried at 55?C until constant mass was reached 4-7 days). Most droppings weighed 10 to 30 g; about 80% of the wet mass of each dropping was lost in drying. Droppings that initially weighed more than 10 g were divided and a portion taken for drying. Phosphate-buffered saline with gelatin (pH 7.4) was added to each dropping at a mass:volume ratio of 1:8. The fecal material was broken up with a glass rod, stirred, and left to soak overnight at 4?C. On the next day the solution was centrifuged (6,000 rpm, 10 min), the supernatant decanted, and aliquots removed and frozen for subsequent assay. Estradiol and testosterone levels in fecal samples were measured by radioimmunoassay as described by Cockrem and Rounce (1994) for chicken droppings. Cross-reactions of the estradiol antiserum with other steroids included estrone (1.3%), estriol (0.24%), and testosterone, progesterone, and androstenedione (all <0.004%). The testosterone antiserum cross-reacted with: dihydrotestosterone (34%); 5f-androstan-3a, 17,Bdiol (3.8%); 11-hydroxytestosterone (3.3%); three other androgens (2-3%); and other steroids (<1%). Serial dilutions of buffer extracted Kakapo samples were parallel to the standard curves for both hormones.
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Dec 1, 2002
Yoshino K + 2
Open Access