Backyard Bird Monitoring - The Data

Project: 

Happy New Year!  As it is a brand new year, I thought I would start by reflecting on the backyard bird monitoring data collected during the past 5 years. A total of 49 different bird species were recorded during the 1402 garden surveys conducted between January 2009 and December 2013. The top 24 species were as follows:

It is worth noting that this is very much an urban profile. We have not recorded a single house sparrow during our five-minute bird counts in the Brook Waimarama Sanctuary.

Total numbers of birds recorded January 2009 to December 2013

House sparrow

9551

 

 

 

Mallard duck

204

Silvereye

 

4800

 

 

 

Goldfinch

191

Starling

 

2026

 

 

 

Dunnock

191

Blackbird

 

1664

 

 

 

Greenfinch

168

Chaffinch

 

952

 

 

 

Yellowhammer

141

Tui

 

860

 

 

 

Black-backed gull

124

Fantail

 

804

 

 

 

Australiasian Harrier

 

117

Song thrush

677

 

 

 

Grey Warbler

108

Welcome swallow

645

 

 

 

Kingfisher

101

California quail

336

 

 

 

Paradise shelduck

92

Kereru

 

220

 

 

 

Redbilled gull

67

Bellbird

 

219

 

 

 

Spur-winged plover

54

         

 

It is great to see tui, fantails, kereru (NZ pigeon) and bellbirds making it into the top 12. I doubt anyone is surprised to see that house sparrows dominated. They even outnumbered the ubiquitous silvereyes almost 2 to 1...or did they?  Let’s take a closer look at the top 12 species.

The table and graph below are the average number of birds recorded in garden surveys in which birds were fed. Please note that the sample size from 2009 was much lower than those of subsequent years.

Year

No. of Surveys

Bellbird

Blackbird

California Quail

Chaffinch

Fantail

House Sparrow

Kereru

Silvereye

Song Thrush

Starling

Tui

Welcome Swallow

2009

28

0.14

1.64

0.11

1.00

0.25

10.32

0.14

3.89

0.86

1.82

0.50

0.39

2010

155

0.31

1.50

0.59

0.81

0.39

9.73

0.16

4.55

0.67

1.48

0.75

0.25

2011

194

0.16

1.17

0.19

0.87

0.60

8.01

0.11

4.04

0.51

1.34

0.59

0.28

2012

179

0.17

1.17

0.30

0.69

0.34

10.11

0.07

3.86

0.56

1.34

0.53

0.69

2013

151

0.16

1.36

0.20

1.04

0.46

10.95

0.23

3.18

0.40

1.26

0.70

0.71

Now look at the averages from gardens in which birds were not fed:

Year

No. of Surveys

Bellbird

Blackbird

California Quail

Chaffinch

Fantail

House Sparrow

Kereru

Silvereye

Song Thrush

Starling

Tui

Welcome Swallow

2009

35

0.06

1.60

0.17

0.37

0.29

4.23

0.09

3.40

0.51

1.46

0.51

0.37

2010

136

0.04

1.15

0.04

0.59

0.57

4.08

0.08

3.06

0.45

1.42

0.45

0.24

2011

143

0.07

1.00

0.19

0.41

0.66

3.41

0.17

2.29

0.38

1.82

0.62

0.48

2012

226

0.16

1.02

0.21

0.51

0.66

4.48

0.29

3.13

0.40

1.40

0.71

0.47

2013

155

0.17

1.03

0.22

0.52

1.03

3.46

0.11

2.97

0.42

1.52

0.55

0.58

 

In surveys in which birds were not fed, silvereyes almost equalled house sparrows. Feeding the birds more than doubled the number of house sparrows in a garden survey, brought in 1 or 2 additional silvereyes and maybe more chaffinch, blackbirds and song thrush, but made little difference to the other species in the top 12. For the purposes of this preliminary analysis, I did not distinguished between the different types of food supplied, perhaps another day.  

The above figures are averages, so what does that mean?  Total birds counted divided by the number of surveys. One may think of an average of 0.25 to be equivalent to 1 bird counted in 1 out of every 4 garden surveys.  However, this may not be true to reality. Two birds counted in 1 out of 8 garden surveys also equals an average of 0.25. Ten California Quail counted in 1 out of 40 gardens also equals an average of 0.25. So looking purely at averages tells us only part of the story. They give us a rough idea of relative population sizes, but tell us little if anything about how a species is distributed or the likelihood that it will be spotted during our garden survey. The next pair of tables and graphs shows the percentage of garden surveys in which each species were recorded as present.

As before, let’s look first at garden surveys in which the birds were fed:

Year

No. of Surveys

Bellbird

Blackbird

California Quail

Chaffinch

Fantail

House Sparrow

Kereru

Silvereye

Song Thrush

Starling

Tui

Welcome Swallow

2009

28

10.71

85.71

3.57

53.57

17.86

96.43

7.14

67.86

46.43

67.86

39.29

14.29

2010

155

18.71

77.42

8.39

41.29

24.52

95.48

7.10

69.03

47.10

46.45

38.71

10.32

2011

194

9.28

70.10

5.67

43.81

30.41

92.27

2.58

72.68

35.05

46.39

28.35

13.92

2012

179

11.73

67.60

7.82

36.87

26.26

99.44

3.91

69.83

44.13

49.72

30.17

24.02

2013

151

11.92

72.19

5.96

48.34

30.46

94.70

7.28

65.56

29.80

45.70

39.74

13.91

 

 

 

Now unfed:

Year

No. of Surveys

Bellbird

Blackbird

California Quail

Chaffinch

Fantail

House Sparrow

Kereru

Silvereye

Song Thrush

Starling

Tui

Welcome Swallow

2009

35

2.86

85.71

8.57

25.71

20.00

94.29

5.71

65.71

42.86

54.29

31.43

28.57

2010

136

2.94

69.12

2.21

28.68

32.35

81.62

4.41

64.71

31.62

49.26

28.68

16.91

2011

143

6.29

63.64

3.50

22.38

38.46

79.02

8.39

54.55

30.77

41.96

37.76

15.38

2012

226

14.16

71.24

5.31

30.09

36.28

84.51

16.37

62.39

30.53

46.02

42.92

25.22

2013

155

13.55

68.39

4.52

31.61

43.87

80.65

9.68

56.77

29.03

50.97

30.97

29.03

 

So what can we glean from this?  Looking at house sparrows again, they were recorded in most garden surveys, around 95% of those in which food was supplied and around 80% in those in which it was not. The more than doubling of the average number of sparrows in the gardens in which food was offered was primarily due to larger groups of birds present rather than a greater likelihood of seeing them. I produced another pair of graphs showing the average numbers of birds recorded where present (i.e. nil values were excluded) which confirms this, but I will spare you these graphs as you must be approaching graph fatigue by now. (If you’d like to see them, I’d be happy to send them to you).

You can examine the above tables and graphs at your leisure, but I’d like you to ponder the following:

1)     The percentage of gardens in which bellbirds were recorded as present remained more or less constant (~10%) in gardens where birds were fed, but increased from less than 3% to ~14% in gardens in which birds were not fed.

2)     Fantails were reported more often in gardens in which birds were not fed.  Are they intimidated by house sparrows or do observers fail to notice them while busy counting dozens of house sparrows?

3)     Despite varying sample sizes, the results remained quite consistent over the past 5 years, providing us with a terrific baseline against which to measure possible changes as a result of the fence being erected around the Brook Waimarama Sanctuary or other environmental changes.

 

Thank you for all your contributions.  Keep up the good work!

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