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Flora & Fauna - Bird Nest Box Scheme - 2013

Introduction

This report covers the fifth bird breeding season since 33 boxes were sited across the Harnham Water Meadows in 2009. Since 2012 when one box was taken apart for use for spares, only 32 boxes have been available for use.

The available nest boxes in place for the 2013 breeding season were:

1. 15 Blue Tit nest boxes with a nest hole diameter of 28mm and designed to exclude larger bird species.

2. 15 similar nest boxes with a nest hole entrance diameter of 32mm designed to allow access for Great Tits and similarly

sized or smaller, hole nesting species.

3. 1 unique open-fronted nest box with a narrow 1 inch slit across the front of the nest box under the overhanging hinged roof.

4. 1 nest box of special design for Treecreepers.

The persistently cold Winter of 2012/13 never wanted to release its grip. Temperatures remained well below average until the beginning of May with plant growth, trees coming into leaf and blossoming, and insect activity being drastically retarded. Bird nesting activity which should have commenced during mid April only happened very slowly, and never really gained momentum until the middle of May.

Clearly, with the long cold Winter lasting so long, birds were slow to gain breeding condition. Since the cold had also affected the availability of insects and larvae for food, the earlier hatching clutches suffered above average mortality. Therefore, fledged juvenile ratios in relation to numbers of eggs laid were low for this season.

Interestingly, two separate pairs of Great Tits produced two broods. Usually Blue and Great Tits are single brooded, but the later clutches fared better with fine and warm weather from mid June and through July.

Nest box disturbance is always kept to a minimum by not opening lids of nest boxes more than once per week, and if a nest is seen to be being brooded, there is never any attempt to disturb an adult bird just for the sake of closer inspection of the contents. A pretty accurate assessment of activity within a nest box can be ascertained when nestlings are approaching fledging as they can then be counted easily and quickly whilst the adults are likely to be away from the nest foraging for food . Any dead nestlings are quickly removed if it is possible to do so in order to reduce the risk of infection to the remaining nestlings from decomposing corpses. Often, any unhatched eggs become visible after fledging nestlings have fledged from the nest, so then the initial clutch size and mortality can be reasonably accurately calculated.

Determining precise numbers of eggs laid without disturbing brooding adults, and knowing how some eggs and nestlings disappear without any defining reason, and without being on hand to watch for juveniles actually fledging the nest, so then it cannot be possible to be wholly accurate with figures in a scheme such as this. Merely that with the same processes being employed year on year for recording purposes, so then  increasing or decreasing trends will become apparent.

Nest Box Occupancy

The occupancy levels of the nest boxes has been rising year on year since the project started. Despite a long cold Winter, a further increase in occupancy was recorded for this breeding season.

Historically, and including this year 2013, the levels of occupancy to the egg laying stages have been:

2009       9 occupied nest boxes (27.27%) –  8 Blue Tits and 1 Great Tit

2010     12 occupied nest boxes (36.36%)  –  9 Blue Tits and 3 Great Tits

2011     14 occupied nest boxes (73.68%)  – 11 Blue Tits and 3 Great Tits

2012     18 occupied nest boxes (56.25%) – 12 Blue Tits and 5 Great Tits – and 1 Wood Mouse!

2013     23 occupied nest boxes (71.87%)  – 16 Blue Tits and 7 Great Tit

Egg Laying and Fledging Analysis

Absolute accuracy of data cannot be possible without disturbance to brooding adults or nestlings, and since this is not done, so the figures in this report are calculated only from known figures based on actual observations of nest contents, and informed conclusions drawn from those.  

Similarly, because it is not sensibly possible to watch for the moment when juveniles fledge the nest, so then some assumptions have to be made regarding the perceived number of nestlings that it is believed have fledged taking into account as accurately as possible known facts such as numbers of unhatched eggs recovered from nests, and numbers of nestlings that have perished and those that remain alive, in the nest. Absolute accuracy is not possible.

BLUE TIT - Breeding Data 2013

104 eggs were laid in 16 boxes. Clutch size varied from a minimum of 3 (probably a deserted partial clutch) to a maximum of 10. Eliminating 2 nests with a total of 8 eggs which were deserted and the eggs thus did not hatch, this gives 14 nests with a total of 96 eggs where activity reached the hatching of eggs stage, an average of 6.86 eggs per occupied box.

28mm hole-entrance diameter nest boxes suitable for Blue Tits – 15 in place

11 boxes were occupied by breeding Blue Tits producing an assumed 20 fledged juveniles.
2 boxes apparently deserted when a total of 8 eggs had been laid.
4 boxes remained unoccupied.

32m hole-entrance diameter nest boxes suitable for both Great and Blue Tits – 15 in place

5 boxes were occupied by breeding Blue Tits producing an assumed 22 fledged juveniles.

Therefore, excluding 2 nests totalling 8 eggs which failed to hatch presumably because of desertion, then the  96 eggs laid in 14 continuously active nests produced an assumed 42 nestlings that reached the fledging stage.

GREAT TIT - Breeding Data 2013

41 eggs were laid in 7 boxes. Clutch size varied from a minimum of 4 to a maximum of 7. Eliminating 1 nest with a total of 6 eggs which was deserted and thus the eggs did not hatch, this gives 6 boxes with a total of 35 eggs where activity reached the hatching of eggs stage, an average of 5.83 eggs per occupied box.

6 boxes of the 32mm hole-entrance type were occupied plus the narrow slit-entrance box. Sadly, this box contained 6 eggs when it became deserted.

32mm hole-entrance diameter nest boxes suitable for Great Tits and other species – 15 boxes in place

6 boxes were occupied by breeding Great Tits producing an assumed 17 fledged juveniles.
5 boxes were occupied by Blue Tits as detailed above.
4 boxes remained empty

Narrow slit front-entrance nest box – 1 in place

This box was occupied by Great Tits and 6 eggs were laid. Sadly, this nest was then deserted.

Therefore, excluding 1 nest totalling 6 eggs which failed to hatch presumably because of desertion, then the 35 eggs laid in continuously active nests produced an assumed 17 nestlings that reached the fledging stage.

Special Design Treecreeper Box.

This box has not attracted any activity since being placed in 2009. It will be removed for placing in another position for the 2014 breeding season with the aim for it to receive more attention.

Summary of Nest Box Success in 32 Available Nest Boxes (33 boxes 2009 to 2011)

The following figures are annual averages of all nests where hatching of eggs has taken place. Nests with eggs laid but then been deserted prior to the hatching time, are excluded.

BLUE TIT

Year

Number of nests

Number of

eggs

Average number of

eggs per box

Number of fledged juveniles

Average Number of fledged juveniles per box

Percentage of fledged juveniles to eggs laid

2009

8

43

5.38

30

3.75

69.77%

2010

9

70

7.78

52

5.78

74.28%

2011

11

74

6.73

48

4.36

64.86%

2012

11

74

6.73

50

4.55

67.57%

2013

14

96

6.86

42

3

43.75%

 

Annual average over 5 year period 2009 to 2013

10.6

71.4

6.7

44.4

5.06

64.05%

GREAT TIT

Year

Number of nests

Number of

eggs

Average number of

eggs per box

Number of fledged juveniles

Average Number of fledged juveniles per box

Percentage of fledged juveniles to eggs laid

2009

1

2

2

2

2

100.00%

2010

4

20

5

9

2.25

45.00%

2011

3

20

6.67

19

6.33

95.00%

2012

4

25

6.25

18

4.5

72.00%

2013

7

50

7.14

23

7.14

46.00%

 

Annual average over 5 year period 2009 to 2013

3.8

23.4

5.41

14.2

4.44

71.60%

Conclusions

In farming, the weather is a major factor in determining what success rates for crops and animals are likely to be. So it is reflected just the same in the wild world of birds. In 2013, the prolonged cold Winter and associated feeding difficulties lots of birds would have faced, meant that nest building and thus the whole breeding season was about two weeks later than normal.

Another issue with cold weather and probable low food supplies would mean that birds would not probably have been in optimum breeding condition.

For the 2013 bird breeding season on the Harnham Water Meadows, two aspects of the season were notable.

Firstly, and gratifyingly, the number of nest boxes in occupancy continues to rise from 9 boxes in 2009 to 21 in 2013. Clearly, the conversion of the original open-fronted boxes to hole-entrance boxes has proven to have been instrumental in wider usage of the boxes.

Secondly, and not so gratifyingly, nor surprisingly given the very cold Spring, the percentage of birds that is assumed to have satisfactorily fledged the nests was sharply down when measured against the number of eggs laid and compared similarly with previous years.

This was demonstrated by more infertile eggs being laid indicating birds were not in optimum breeding condition, and a higher number of nestlings perishing in the nests as a result of chilling and/or insufficient food availability for foraging adults to feed their brood.

Unusually, 2 separate Great Tit boxes had second broods. 1 certainly followed on from a wholly failed first brood. By the time these second broods were hatched towards the end of June, the weather had turned into hot and dry conditions thus ensuring these second broods did well thus increasing the Great Tit production levels.

There are about 4 boxes that will be re-sited before the commencement of the 2014 breeding season since they have remained unused for a few years.

As ever, additional support, especially by way of executing urgent running repairs to some boxes, has been once again enthusiastically given by John Beckett and Jan Fitzjohn to whom I am extremely grateful. Thank you …... and your various skills will be called upon again very soon!

Report by John Vickerman – October 2013

Registered Charity No: 1001360

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