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North Island Robins And Moisure On Essay

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How the abundance and diversity of insect populations in two areas of the Wellington region are affected by moisture, pH and depth of leaf litter, and what this could mean for the survival of the Petroica longipes (North Island Robin) population.

Franziska Plimmer
Candidate Number: 003740-0019
Word Count: 3824

Abstract
This research assignment looks at how the abundance and diversity of insect populations in the Wellington region are affected by moisture, pH and depth of leaf litter, and what this could mean for the survival of the Petroica longipes (North Island Robins) population. Though initially the research was going to take place on Matiu Island, it was carried out in Eastbourne and in Zealandia, a native wildlife sanctuary. Both these areas in Wellington were chosen because of their similarities to Matiu Island. In Eastbourne pitfall traps were placed in selected moist and dry areas for three weeks to determine levels of invertebrate abundance and diversity. In those same areas moisture, pH and depth of the leaf litter (referred to as leaf litter quality) were measured by using a soil probe and a ruler. To link this back to the research question, ten minute observations of P. longipes and other birds were recorded at Zealandia in both a moist and dry area, as well as recording leaf litter quality measurements.

It is important to understand the factors that could affect the success of translocations. From this study’s findings, a factor to consider could be how moisture affects invertebrate abundance. This is due to the findings showing that as leaf litter quality increased so did the P. longipes’ food source (the ground-dwelling invertebrates). Findings also showed that there were more P. longipes found in moist areas than in dry areas, supporting the idea that lack of moisture could be a reason for the P. longipes’ low survival rates on Matiu Island. Word Count: 259

Acknowledgements
I am very grateful to George Gibbs who helped the project get off the ground and who helped me design my pitfall traps. Thanks to Zealandia for permission to do research there. I owe special thanks to my project supervisor who answered so many of my questions and had to read this many times. And of course to my mother who helped me identify birds and insects at Zealandia.

Contents
Introduction ........................................................................................................................................ 1 Method of Investigation ..................................................................................................................... 2 Location........................................................................................................................................... 2 Maps................................................................................................................................................ 3 Pitfall traps in Eastbourne................................................................................................................... 5 Step by step method ....................................................................................................................... 7 Measuring leaf litter quality................................................................................................................ 9 Equipment ....................................................................................................................................... 9 Bird Observations in Zealandia ......................................................................................................... 10 Step-by-step method .................................................................................................................... 10 Raw Data ........................................................................................................................................... 11 Observations ..................................................................................................................................... 12 Results ............................................................................................................................................... 14 Discussion.......................................................................................................................................... 21 Evaluation ......................................................................................................................................... 23 Conclusion ......................................................................................................................................... 25 Bibliography ...................................................................................................................................... 26 Appendix ........................................................................................................................................... 28

Introduction
I have always wanted to know answers to questions, so when proposed a question without an answer I was intrigued to find out more. The question was simple, why did the Petroica longipes (North Island Robins) that had been introduced to Matiu Island have a low survival rate? A variety of ages of P. longipes were introduced to Matiu Island in August 2007, 10 from Zealandia (a conservation sanctuary) and 35 from Kapiti Island (Karori Sactuary Trust (2014) ). Due to the P. longipes’ translocation success from Kapiti to Zealandia and the fact that the P. longipes population on islands like Kapiti, Mana and the Chathams are thriving, it was assumed that the P. longipes would also do well on Matiu Island. The P. longipes population decreased in steps rather than a constant decrease. The rangers noticed the change in March and May and now there is only one known P. longipes on the island (Greenman, 2013). The end of March and May is the driest time on Matiu Island, an Island already known for its lack of moisture due to there being no natural water source. They were introduced to two different locations but all migrated to a moist area near the wharf called the bullet track with mature forests (Greenman, 2013). In a study done on Matiu Island, it was found that there was twice the amount of beetles in the mature forest as in the shrub land (Gibbs & Watts, 2000). This shows that the P. longipes would have had a better food source at the bullet track. As the P. longipess’ food source is a vital part of their survival, I decided to look into invertebrates. This led me to the following research question: “How the abundance and diversity of insect populations in two areas of the Wellington region are affected by moisture, pH and depth of leaf litter, and what this could mean for the survival of the Petroica longipes (North Island Robin) population.” The P. longipes forage in leaf litter for a variety of ground-dwelling invertebrates, from large Wetas to small stick insects and earthworms (Complete Book of New Zealand Birds, 1985). By studying what affects ground-dwelling invertebrates, data could shed light on the P. longipes’ low survival rate on Matiu Island. The main insect on Matiu Island are spiders, ground, tree and giant Wetas, false spiders, stick insects, flies and beetles (especially the cloptra beetle) (Greenman, 2013). I hypothesised that it was most likely going to be the moisture that affects invertebrate populations, as lack of moisture leads to fatality much

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more quickly than lack of food. Consequently one moist area and one dry area were investigated.
This research is worthy of investigate because it may indicate why P. longipes had a low survival rate on Matiu Island and therefore help the department of conservation (DOC) with future translocations, DOC being the government department in New Zealand that looks after conservation issues. New Zealand has a rich history in conservation. When settlers arrived in around 1840 approximately fifty percent of native bush was deforested for houses and farming. Settlers also introduced predators such as possums, rats, stoats and mice. This saw a rapid decrease in native bird species such as the iconic Kiwi and Moa. Such predators prey on young P. longipes and their eggs (Complete Book of New Zealand Birds, 1985). However in the late 20th century conservation efforts in New Zealand began to increase, predator-free reserves (such as Matiu Island) and new guidelines were created. Native bird species are translocated to these reserves so that endangered populations can survive and reproduce. Some translocations are successful and some are not, such as the ...

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