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Nestbox Project Data

At the moment detailed data presentation starts with 2009. We aim to add some basic comparison of data for the first two years of the project (2007 and 2008).

TABLE 1. General data for 2009

Total number of boxes

60

Boxes used by an owl or owl pair

11 (18%)

Boxes used for breeding

10 (16%)

TABLE 2. Clutch sizes 2009

Clutch size

Number of clutches

Number of eggs

1 egg

0

0

2 eggs

4

8

3 eggs

6

18

4 eggs

0

0

TOTAL:

10

26

AVERAGE:

—

2.6

TABLE 3. Detailed data breakdown for 2009

EGGS

CHICKS

BOX No.

Laid

Predated

Infertile

Other

Hatched

Predated

Died

Other

Fledged

74

3

3

3

76

3

Egg lost

2

1

1

79

2

1

1

1

88

3

Egg lost

2

1

1

99

2

2

2

103

2

2

0

0

114

2

2

2

117

3

3

0

0

119

3

2

1

0

0

122

3

Egg lost

2

1

1

TOTAL:

26

4

5

3

14

0

3

0

11

Notes: There are 60 owl nestboxes, numbered — to —. Laying weeks (inferred from hatching times) are known for six pairs: one pair laid between 5 and 11 March (week 10), three pairs laid 12-18 March (week 11), and two pairs laid 19-25 March (week 12).

What is notable in Table 4 is the markedly different success rate for three- and two-egg clutches, with the smaller broods having nearly twice the success rate of the larger broods (63% of eggs laid resulted in a fledgling versus 33%). With the two-egg broods, all the chicks that hatched went on to fledge, whereas with the three-egg broods three chicks out of the nine that hatched died. However, the sample size is probably too small for this different success rate to be seen as significant.

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TABLE 4. Success rates for different-sized clutches 2009

BOX No.

Laid

Hatched

Fledged

Cause of loss

74

3

3

3

—

76

3

2

1

Egg lost, chick died

88

3

2

1

Egg lost, chick died

122

3

2

1

Egg lost, chick died

117

3

0

0

All eggs infertile

119

3

0

0

2 eggs predated, 1 infertile

TOTAL:

18

9 (50%)

6 (33%)

99

2

2

2

—

114

2

2

2

—

79

2

1

1

Egg infertile

103

2

0

0

Both eggs predated

TOTAL:

8

5 (63%)

5 (63%)

Dani Studler's

nestbox project —

data for 2009

A three-chick brood from 2009