Comparing 2006 foraging data using 2005 breeding success

One of the objectives of this research was to assess why only a small proportion of female kakapo attempt to breed in low rimu mast years on Codfish Island, by determining if home range size or habitat types used by females may influence their ability to breed. Unfortunately during 2006 when I conducted field work there was a low rimu mast and no females attempted to breed, so I was unable to make any direct comparisons between foraging behaviour and breeding attempts during 2006. As a next best alternative I compared foraging home ranges for individuals in 2006 based on their breeding success in 2005.

2.6.1 Breeding success defined

The breeding success of an animal could be determined by a range of measures including clutch size, number of fertile eggs laid and hatching or fledging success. However in kakapo the outcome of breeding attempts is often influenced by a number of variables not directly related to the fitness of individual females. For example a large proportion of eggs are infertile, eggs have a low hatch rate (Elliott et al., 2006) and nests are often manipulated with eggs and chicks being moved between nests (Elliott et al., 2001). For these reasons the breeding success of a female in the 2005 breeding season was defined in this research by if she attempted to breed, rather than the outcome of any nesting attempt.

If a female nested, regardless of the outcome of that nest, then it was considered that she had successfully bred so was called a 2005 “breeder”. If a female did not produce a nest during the 2005 breeding season then it was considered that she did not successfully breed and was referred to as a “non-breeder” during 2005. It is important to note that the status of breeder or non-breeder, only applies to breeding success in 2005. As explained in section 2.2.2, the females that did not breed in 2005 had all previously nested on Codfish or other islands, with the exception of Jane, indicating that they had the ability to breed but did not in the low rimu mast year of 2005.

2.6.2 Comparison of locations from breeding and non-breeding years

To be able to compare foraging home ranges for individuals in 2006 based on their breeding status in 2005, I needed to be fairly certain that females used similar home ranges in both of these years. Research by Farrimond et al. (2006) suggests that breeding does not alter home range size, as rearing young did not require expansion of a female’s home range. Radio- tracking studies by Farrimond et al. (2006) on Codfish Island during September - January of 2001/ 2002 and 2002/ 2003 found that home ranges of adult female kakapo were similar in these breeding and non-breeding years.

2.6.3 Statistical methods

To determine if variation occurs in an individual’s home range between breeding and non- breeding years, location data from the autumn period of 28 March to 30 May was collated from two previous breeding years (2002 and 2005) and two previous non-breeding years (2003 and 2004). Location data for these four years was mostly day-time roosting data collected during routine monitoring by NKT staff using a mixture of triangulations, sightings

Chapter 2 General Methodology and snark records. (A snark is a portable electronic device placed in the field that records any visits of transmitted kakapo to within several metres of the receiver). Six of the 18 adult female kakapo in this study could not be included in this analysis as they were not present on Codfish Island for all years between 2002 and 2006 (Appendix 1 and Appendix 4). For the remaining 12 females that were included, there were considerably fewer locations available for each individual in each of these four years compared to the number of locations collected during the 2006 field season. The number of locations collected during these four years was variable between individuals and years (Appendix 4).

Due to the limited and variable quantity of location points available for adult female kakapo from the two breeding and two non-breeding years, it was not possible to estimate home range sizes for these years that would have been comparable with home range estimates for 2006. Instead the proportion of location points collected between 28 March and 30 May from previous years that overlapped with the 2006 minimum convex polygon (MCP) foraging home range (estimated in Chapter 3) was calculated for the 12 females for each year (Appendix 4).

A mixed-model ANOVA was used to determine if the proportion of points from each year overlapping with the 2006 foraging home range was affected by a number of fixed and random variables. This analysis method accounts for the non-independence of the data arising from multiple years of locations on the same adult female kakapo. The fixed variables included in the mixed-model ANOVA were the year (2002 to 2005), if the year was a breeding or non-breeding year, the breeding status of the individual (breeder or non-breeder during 2005) and the size of the MCP home range for autumn 2006. The individual female, nested within 2005 breeding status, was included as a random factor in the model. The ANOVA was performed in the statistical package R (R Development Core Team, 2005). 2.6.4 Results and implications

There was no significant difference in the proportion of location points that overlapped with the 2006 foraging home range between breeding and non-breeding years (p = 0.759, t = 0.309, df = 37). The breeding status of an individual in 2005 did not influence the proportion of points that overlapped with the 2006 foraging home range (p = 0.164, t = 1.51, df = 9) and nor did the size of the foraging home range (p = 0.568, t = 0.593, df = 9).

These results suggest that adult female kakapo on Codfish Island occur in similar areas during breeding and non-breeding years, and supports research by Farrimond et al. (2006) that adult female kakapo on Codfish Island use similar home ranges in breeding and non-breeding years. As home ranges do not appear to differ significantly in their location between breeding and non-breeding years, home ranges used by individuals in the breeding year of 2005 and the non-breeding year of 2006 are most likely similar, thus allowing a comparison of 2006 foraging home ranges based on the breeding success of individuals in 2005.