ESTUARY ATTRIBUTES AND WADER POPULATIONS

Relationship between Physical Characteristics of Estuaries and the Size and Diversity of Wader Populations in the North Island of New Zealand

Acknowledgements

This study was undertaken while Michael Whelan was on sabbatical at NIWA and supported by Southern Cross University. The study was part of NIWA's programme 'Effects of suspended sediment on coastal and estuarine ecosystems funded by the Foundation for Research Science and Technology (contract C01X0024). Our special thanks go to the several hundred people who, over the years 1983-1994, assisted with the OSNZ national wader count scheme.

Abstract

Maximum wader abundance and the maximum number of species recorded (1983-1994) at 94 estuaries on the North Island, New Zealand were related to physical attributes of the estuaries using General Linear Modelling techniques. Parameters describing the estuary type, area, tidal influence, catchment area, catchment rainfall, intertidal area and temperature were used as independent variables.

Analysis revealed strong positive relationships between the size and diversity of a wader population and estuary. A negative relationship between catchment runoff and wader abundance and diversity existed in some estuaries. The model predicted that relatively small estuaries (100 to 999 ha) could support large, diverse wader populations if catchment runoff was low.

A map of estuaries predicted by the model to support large diverse populations of wading birds is presented. This study highlights the value of large estuaries in New Zealand in maintaining large populations and high species diversity of migratory and non-migratory waders.

Keywords: waders, estuaries, populations, distributions

Table of Contents

Acknowledgementsii

Abstractiii

CHAPTER 1: INTRODUCTION1

CHAPTER 2: LITERATURE REVIEW4

CHAPTER 3: METHODOLOGY17

Preliminary Analysis22

General Linear Modelling22

Classification24

CHAPTER 4: RESULTS25

Preliminary Analysis25

General Linear Model26

Significant Main Effects In The Models28

Significant Interaction Terms In The Models33

Classification36

CHAPTER 5: DISCUSSION & CONCLUSION39

Estuary42

REFERENCES45

CHAPTER 1: INTRODUCTION

Wading birds are an important and highly visible component of estuaries. Waders worldwide are being put under pressure from recreational use of estuaries (Davidson & Rothwell 1993), hunting, habitat loss, drainage for agriculture, pollution and fishing (Parish et al. 1987; Scott & Poole 1989). Morrison et al. (2001) found that the number of shorebirds in Canada had declined from 1974 to 1999 but could not identify any single cause for the decline. Changes in the hydrology of estuaries have led to changes in wader populations (Maisonneuve 1993, Collazo et al. 1995). Burton (2001) attributed a decline of 87% of birds in Cardiff Bay to hydrological changes in the estuary caused when a barrage was built across the mouth of the bay. New Zealand estuaries support over 160,000 waders of local breeding species and a similar number of migrants from the northern hemisphere (Sagar et al. 1999). Most of the populations of waders that breed in New Zealand do so away from estuaries and a recent review of their statuss (Dowding & Murphy 2001) concluded that most are under increased predation pressure from introduced mamals. After breeding, most of these waders move to estuaries where they co-occur with the thousands of migrants from the northern hemisphere. Sagar et al. (1999) found that most waders used relatively few estuaries, especially the large harbours of North Island, Farwell Spit ...