A thesis submitted in partial fulfillment of



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NESTING ECOLOGY AND COMMUNITY STRUCTURE OF CAVITY-NESTING BIRDS IN

THE NEOTROPICAL ATLANTIC FOREST


by
Kristina Cockle

B.Sc., University of British Columbia, 2000

M.Sc., Dalhousie University, 2003

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
in
The Faculty of Graduate Studies

(Forestry)


THE UNIVERSITY OF BRITISH COLUMBIA

(Vancouver)


August 2010
© Kristina Cockle, 2010

ABSTRACT
Tree cavities are proposed to limit populations and structure communities of cavity-nesting

birds, making these birds particularly vulnerable to anthropogenic activities that destroy potential

nest trees. The greatest diversity of cavity-nesting birds is found in tropical rainforests, yet little is known about the ecology or conservation of these birds. I studied how the production, consumption and loss of tree cavities structure a cavity-nesting community in one of the five most important global biodiversity hotspots, the subtropical Atlantic forest of Argentina.

I found that the cavity-nesting community in the Atlantic forest is structured primarily around the production and persistence of high, deep, non-excavated cavities in large live trees. I

show the first experimental evidence that the supply of tree cavities limits the breeding density of

secondary cavity-nesting birds (species that do not excavate their own cavity) in a tropical forest.

Conventional tropical logging strongly reduced cavity availability: logged forest had half the

basal area of primary forest, but only one third the density of large trees, nine times fewer cavities

suitable for nesting birds, and 17 times fewer active nests. My results suggest a severe impact of tropical logging on the abundance of cavity-nesting birds, and a need for management strategies that conserve large live cavity-bearing trees. In contrast to North America where vertebrate

excavators create most of the nest cavities for secondary cavity nesters, but similar to sites

outside of North America, 80% of nests of secondary cavity nesters in the Atlantic forest were in

cavities created by natural decay processes. These non-excavated cavities were often in live

stems or branches. The predominance of excavated cavities in North America and non-excavated

cavities elsewhere can be explained partly by high rates of persistence of excavated cavities at a site in North America and low rates of persistence of excavated cavities at a site in Europe and my site in Argentina. To conserve cavity-nesting birds of the Atlantic forest, I recommend a combination of policies, economic assistance, environmental education, and technical support for forest managers and small-scale farmers, to maintain large healthy and unhealthy trees in commercial logging operations and on farms.



TABLE OF CONTENTS

Abstract

…………………………………………………………………………………….…

ii




Table of Contents

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iii




List of Tables

………………………………………………………………………….….….

v




List of Figures

………………………………………………………………………...………

viii




Acknowledgements

…………………………………………………………………….……..

xi




Co-authorship Statement

……………………………………………………………………

xiii




Chapter 1. General Introduction and Thesis Overview

……………………………...……

1




Tree cavities and the ecology and conservation of cavity-nesting birds

…………………..

1




Cavity-nesting communities in tropical and subtropical forests in the Neotropics

…………..

2




Cavity-nesting communities in the Atlantic forest

………………………………………...

4




Thesis Objectives

...……………………………………………………………………..

4




Study Area

…………………………………………….………………………………….

5




Experimental plots

………………………………………………………………………

6




Cavity-nester community

………………………………………………………………...

6




General Field Methods

………………………………………………...…………………

7




Thesis Overview

…………………………………………………………………………..

8




References

…………………………………………………………………………..…….

15




Chapter 2. Tree Cavities in the Atlantic Forest: Production and Use by Cavity-nesting Birds


……………………

21




Methods

…………………………………………………………………………………….

24




Study area and field methods

…………………………………………………………….

24




Analyses

……………………………………………………………………………......

25




Results

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27




Discussion

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29




Cavity formation

………………………………………………………………….…….

29




Reuse of cavities

………………………………………………………………………..

30




Body size and nest web structure

………………………………………………………..

31




Conclusion

…………………………………………………………………………………

32




References

…………………………………………………………………………………

38




Chapter 3. Selection of Nest Trees by Cavity-nesting Birds in the Atlantic Forest

……...

42




Methods

…………………………………………………………………………………….

43




Field methods

………………………………………………………………………….

43




Analyses

………………………………………………………………………………

45




Results

……………………………………………………………………………………...

47




Excavators

…………………………………………………………………………….

47




Secondary cavity nesters

……………………………………………………………….

47




Formation of non-excavated cavities

……………………………………………………

48




Discussion

………………………………………………………………………………….

48




Conclusion

…………………………………………………………………………………

50




References

…………………………………………………………………………………

58




Chapter 4. Nest-site Limitation and Effects of High-grade Logging on Cavity-nesting Birds in the Atlantic Forest

………………………

62




Methods

…………………………………………………………………………………….

63




Field methods

………………………………………………………………………….

63




Cavity availability

………………………………………………………………….

64




Cavity occupancy

………………………………………………………………….

64




Resource supplementation

…………………………………………………………

64




Analyses

……………………………………………………………………………

65




Cavity availability

…………………………………………………………………

65




Resource supplementation

…………………………………………………………

65




Results

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66




Cavity availability

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66




Cavity occupancy

…………………………………………………………………….

66




Resource supplementation

…………………………………………………………….

67




Discussion

………………………………………………………………………………….

67




Conclusion

…………………………………………………………………………………

69




References

…………………………………………………………………………………

76




Chapter 5. Global Variation in the Role of Woodpeckers as Tree Cavity Producers And the Persistence of Excavated and Non-excavated Cavities

………………

78




Methods

……………………………………………………………………………………

79




Results

……………………………………………………………………………………...

81




Discussion

………………………………………………………………………………….

82




References




87




Chapter 6. General Discussion and Management Recommendations

……………………

90




Management Recommendations

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95




1. Conserve existing and future cavity-bearing trees in legally commercially-Logged native forest through regulations and financial incentives

……………

97




2. Conserve existing cavity trees and initiate reforestation on small farms

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98
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