ECOLOGICAL CORRELATES
OF BIRD DAMAGE IN A
CANTERBURY VINEYARD
A thesis
submitted in partial fulfilment
of the requirements for the Degree of
Master of Applied Science
at
Lincoln University,
by
Nigel G. Watkins
Lincoln University
1999
For Joan
(21.1.20 - 20.9.98).
... no shallow life you, spinning love and life midst
the company around your hearth.
Suffering fools and finding friends you
made sense of madness and enlightened
us all.
You breathed for the weak, soothed the strong and
the lost saw a beacon close. You
championed the brave too for you
recognised their virtue....
You are our lifeguard, our seamstress, you did not
leave us, you did not die.
ii
Abstract of a thesis submitted in partial fulfilment of the
requirements for the Degree of Master of Applied Science
Ecological correlates of bird damage
in a Canterbury vineyard
by Nigel G. Watkins
Birds are a major pest in vineyards both in New Zealand and overseas. There is a
need for new behavioural research on birds' foraging habits and feeding
preferences in vineyards, as much of the literature to date is anecdotal. Research
on cues to birds' feeding will provide a basis on which new deterrent and control
strategies can be devised.
Spatial-ood temporal bird damage in a small vineyard block was mapped to find if
damage was correlated with grape maturity and environmental factors. Vineyard
and field observations of bird behaviour using video technology combined with
preference experiments aimed to establish the relative roles of grape sugar
concentration and colour in avian selection.
Proximity of vineyards to bird roosts affects damage levels, regardless of differing
maturity between locations. The rate of damage tends to increase exponentially
once grape maturity has passed a threshold of 13 °Brix. Bunches positioned
closest to the ground receive more damage if blackbirds or song thrushes are the
predominant pests.
Both sugar concentration and grape colour were found to affect birds' feeding
preference, but the importance of the two factors varied between years. Black and
green grape varieties were differentially preferred by blackbirds (Turdus meru/a)
and song thrushes (Turdus phi/orne/os) while silvereyes (Zosterops /ateralis)
appeared to have no strong colour preference. It was apparent that there were
other, not assessed, grape factors that also affect selection.
iii
In small unprotected vineyards that are adjacent to bird roosts the entire; grape
crop can be taken by bird pests. Besides removing the roosts, which can be
beneficial shelterbelts in regions exposed to high winds, growers currently may
have no alternative other than to use exclusion netting to keep crops intact. The
differential preferences between bird species for variety characteristics suggest
that any new deterrents and other strategies to deflect birds from grape crops may
need to be species-specific.
Keywords:
Bird damage; grapes; vineyard management; preference; colour;
sugar concentration; bird behaviour; foraging strategy; European blackbird;
Turdus rneru/a; Song thrush; Turdus phi/orne/os; Silvereye; Zosterops /ateralis.
iv
Contents
PAGE
Title
Dedication
ii
Abstract
iii
Table of Contents
v
List of Tables
x
List of Figures
xi
List of Plates
xii
Chapter One
1.0
Introduction
1
1.1
Birds as vineyard and crop pests
2
2
1.1.2 Economic considerations
1.2
History of control efforts and their effectiveness
3
1.2.1 Chemical repellents
3
1.2.2 Non-chemical control of birds
4
1.2.3 Cost-effective control
6
1.3
7
Need for research
1.3.1 Behavioural-centred research
7
1.3.2 Previous research on bird damage to grapes
8
1.3.3 New Zealand research directions
8
1.4
Scope and aim of the thesis
9
1.4.1 Objectives
1.5
9
Structure of thesis
10
1.5.1 Terminology
10
Chapter Two
2.0
Spatial and Temporal Patterns of Bird Damage
at Kotokonui Vineyard in 1997
11
2.1
Introduction
11
2.2
Background
11
2.2.1 How birds select between and within crops
12
2.2.2 Sugar concentration and bird damage in vineyards
12
v
PAGE
2.2.3 Objectives
13
2.3
14
Methods
2.3.1 Study location
14
2.3.2 Damage scoring
15
2.3.3 Measuring spatial patterns of damage
16
2.3.4 Protocol for selection of sample bunches
17
2.3.5 Assessing sugar concentration
18
2.3.6 Assessing the stratification effect
19
2.3.7 Measuring temporal patterns of damage
20
2.4
20
Results
2.4.1 Spatial damage and correlations with sugar levels
21
2.4.2 Stratification effect
23
2.4.3 Temporal damage
23
2.4.4 Sugar concentration assessment
26
2.4.5 Under-ripe and diseased grapes
26
2.5
27
Discussion
2.5.1 General
27
2.5.2 Spatial damage and it's correlates
27
2.5.3 Stratification effect
29
2.5.4 Temporal damage
30
2.5.5 Under-ripe grapes
31
2.5.6 Methodological issues
31
2.5.7 Summary
32
Chapter Three
3.0
i
The Relative Roles of Sugar and Colour in
Bird Damage to Different Grape Varieties
33
3.1
Introduction
33
3.2
Background
33
3.2.1 Role of colour in fruit selection by birds
34
3.2.2 Colours associated with frugivore preference and avoidance
35
3.2.3 Differential susceptibility of grape varieties to bird damage
36
3.2.4 Rationale for this field study
37
vi
PAGE
3.2.5 Objective
37
Methods
38
3.3
3.3.1 Study sites
38
3.3.2 Grape varieties used and source locations
38
3.3.3 Presentation of bunches 1997 and 1998
40
3.3.4 Experiment location and description of hangings
41
3.3.5 Damage scoring and sugar concentration assessment
41
3.3.6 Preference studies
43
3.3.7 Accuracy of bunch sugar concentration
44
3.4
45
Results
3.4.1 Grape sugar concentration
45
3.4.2 Bird preference
46
3.4.3 Comparison of adjacent crop berries in 1998
54
3.4.4 Accuracy of bunch sugar concentration
56
3.4.5 Score consistency
57
Discussion
58
3.5
3.5.1 Effects of sugar concentration and colour
58
3.5.2 Possible effects of surrounding crops
63
3.5.3 Methodological issues
65
3.5.4 Summary
68
,
Chapter Four
4.0
Feeding Behaviour of Birds in Vineyards
69
4.1
Introduction
69
4.2
Background
69
4.2.1 Bird species associated with damage to grapes
69
4.2.2 Diurnal patterns of bird feeding
70
4.2.3 Feeding behaviour
70
4.2.4 Fruit sampling and selection
71
4.2.5 Physiology of taste and smell in birds
72
4.2.6 Research aims and objective
74
4.3
Methods
74
4.3.1 Study sites
74
vii
PAGE
4.3.2 Video arrangement and bunch collection description
74
4.3.3 General feeding behaviour
76
4.3.4 Assessing birds' preference behaviour
77
4.3.5 Single, multiple and return visits in same bout
79
4.4
79
Results
4.4.1 Species composition at vineyard
79
4.4.2 Diurnal patterns of bird feeding
80
4.4.3 Mean consumption and time spent at collections
80
4.4.4 Colour preference
81
4.4.5 Preferences and correlations with sugar content
84
4.4.6 Single, multiple and return visits in same bout
89
4.5
90
Discussion
4.5.1 Species composition
90
4.5.2 Diurnal feeding patterns
91
4.5.3 Behaviour of birds at grape collections
91
4.5.4 Feeding preferences
92
4.5.5 Summary
98
Chapter Five
5.0
Colour Cues and Preference
99
5.1
Introduction
99
5.2
Background
99
5.2.1 Fruit eating by silvereyes in New Zealand
99
5.3
101
Methods
5.3.1 Study site
101
5.3.2 Description of hanging and presentation of bunches
101
5.3.3 Bird damage and sugar concentration assessment
102
5.3.4 General feeding behaviour
102
5.3.5 Assessing birds' preference behaviour
102
5.3.6 Storage of grapes
103
5.4
104
Results
5.4.1 General feeding behaviour
104
5.4.2 Birds' preference for colour
106
viii
;PAGE
5.5
110
Discussion
5.5.1 General feeding behaviour
110
5.5.2 Birds' preferences
112
5.5.3 Methodological issues.
113
5.5.4 Summary
115
Chapter Six
6.0
Conclusion
116
6.1
Summary of findings
116
6.2
Management of vineyards
121
6.2.1 Species causing damage
121
6.2.2 Use of deterrents
121
6.2.3 Habitat management
122
6.3
123
Scope for future research
6.3.1 Methodology employed
124
6.4
126
Concluding remarks
Acknowledgments
127
References
129
Appendices
148
ix
LIST OF TABLES
PAGE
TABLES (captions are abbreviated)
2.1
Relationship between % damage and integer damage scores.
15
2.2
Date and schedule of damage I sugar concentration assessments.
20
2.3
Damage I sugar concentration between roost and 'open' end.
21
2.4
Damage I sugar concentration on high and low sample points.
23
3.1
Varieties used in 1997 bunch hangings.
38
3.2
Varieties and originating sources used in 1998.
39
3.3
Location, schedule and description of bunch hangings.
41
3.4
Damage assessment schedule.
42
3.5
Data collection periods for damage regression analysis.
44
3.6
Sugar concentration variance between varieties in 1997.
45
3.7
Sugar concentration variance between varieties in 1998.
46
3.8
Daily damage rates to black and green bunches at vineyard 1997.
47
3.9
Variables associated with damage to vineyard collections in 1997.
47
3.10
Daily damage rates to black and green bunches at vineyard 1998.
50
3.11
Variables associated with damage to vineyard collections in 1998.
51
3.12
Daily damage rates and mean sugar levels at orchard 1998.
54
3.13
Comparison of °Brix 5-berry mixes vs whole bunch in 1998.
56
3.14
Comparison of °Brix 5-berry mixes vs means of 5-singles in 1998.
56
3.15
Error frequency from 'blind' damage estimates in 1997.
57
3.16
Error frequency from 'blind' damage estimates in 1998.
57
4.1
ANOVA table for species consumption patterns 1997.
82
4.2
ANOVA table for species consumption patterns 1998.
83
4.3
Mean time I mean visitation index for varieties and species.
83
4.4
°Brix readings black and green varieties in videoed collections.
84
4.5
Single, multiple and return visits in same bout (vineyard)
89
4.6
Number of birds making return visits to different coloured bunches.
89
5.1
Varieties, colours, and origins of grapes in bunch collections.
101
5.2
Error frequency from 'blind' damage estimates.
107
5.3
Single, multiple and return visits in same bout (orchard)
109
5.4
Number of birds making return visits to different coloured bunches.
109
x
LIST OF FIGURES
PAGE
FIGURES (captions are abbreviated)
2.1
Perimeter and interior areas of damage sample points.
20
2.2
Chardonnay block - lines of high damage.
21
2.3
Damage on lines on first four assessment dates.
22
2.4
Damage and sugar concentration on vine rows.
24
2.5
Damage and sugar concentration on Chardonnay block.
25
3.1
Predicted relationship - daily damage, °Brix, & colour 1997.
48
3.2
Mean damage to varieties in 1997 (all hangings).
49
3.3
Predicted relationship - daily damage, °Brix, & colour 1998.
51
3.4
Mean damage to varieties in vineyard 1998 (Hanging 1).
52
3.5
Mean damage to varieties in vineyard 1998 (Hanging 2).
53
3.6
Mean damage to varieties in orchard 1998 (Hanging 2).
55
4.1
Mean number visits/day and species of bird visiting collections.
79
4.2
The time of day birds visited the vineyard collections.
80
4.3
Mean time spent and grapes attacked / per bout / bird.
81
4.4
Mean grapes attacked / per bunch / bout / bird / colour.
82
4.5
Mean grapes attacked / per bunch / bout / bird / variety - 97.
85
4.6
Mean grapes attacked / per bunch / bout / bird / variety - 98.
85
4.7
Mean time spent / per bunch / bout / bird / variety - 97.
86
4.8
Mean time spent / per bunch / bout / bird / variety - 98.
87
4.9
Mean visitation index 1997.
88
4.10
Mean visitation index 1998.
88
5.1
Species composition at the orchard.
104
5.2
Diurnal feeding behaviour at the orchard.
105
5.3
Mean time spent feeding / bout.
105
5.4
Mean damage to varieties in bunch collections.
106
5.5
Mean time spent at bunches / bout.
107
5.6
Mean visitation index to bunches.
108
5.7
Mean number of grapes attacked / bout by blackbirds.
108
xi
LIST OF PLATES
PLATES (captions are abbreviated)
PAGE
1.1
Example of bird damage to a vine.
1
2.1
Chardonnay block (the study block) looking down vine rows.
14
2.2
Example of a tagged bunch.
18
2.3
The netting of the remainder of the vineyard.
25
3.1
Bunch collection at Kotokonui Vineyard in 1997.
39
3.2
Bunch collection at Domigan's Orchard in 1998.
40
3.3
Differential damage between coloured bunches in 1998.
62
4.1
Videoed bunch collection at Kotokonui Vineyard in 1998.
75
5.1
Example of silvereye damage to a grape bunch.
100
5.2
Differential damage to variety colours (peck and pluck).
112
xii