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Gordon W Follows
This paper is an Appendix to Bird Populations in a North Yorkshire Woodland
by Gordon W Follows and Ron Gash
Data gathered during 2000 has confirmed that raising boxes from two to four metres above the ground has resulted in increased occupation, particularly by Blue Tits. This is well illustrated by the following graph, which also reveals that the number of Pied Flycatchers using the nest-boxes remains at the very low level of two pairs, albeit at least six singing males were located during early May. Such behaviour has been observed in the past but there was no evidence that these additional birds bred within the study area.
On a more positive note, a singing male Wood Warbler was present in Mell Bank Wood during most of May, the first year since 1992 that birds have been present and most probably attempted to breed. A breakdown of the number of birds using the boxes is given in the table below and with the exception of Pied Flycatchers, overall occupation during 2000 was perhaps about average.
| 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Pied Flycatcher | 15 | 7 | 10 | 8 | 3 | 3 | 1 | 4 | 2 | 2 |
| Redstart | 0 | 4 | 4 | 3 | 0 | 2 | 2 | 1 | 0 | 0 |
| Blue Tit | 10 | 14 | 13 | 14 | 6 | 7 | 12 | 10+ | 16 | 15 |
| Great Tit | 7 | 11 | 11 | 8 | 6 | 8 | 11 | 6+ | 9 | 6 |
| Unidentified Tits | 4 | |||||||||
| Coal Tit | 2 | 1 | 2 | 2 | 2 | 1 | 2 | |||
| Marsh Tit | 1 | 1 | 1 | 1 | 2 | 1 | 1 | 2 | 1 | |
| Nuthatch | 1 | 1 | 1 | 1 | ||||||
| Treecreeper | 1 | 1 | ||||||||
| Total | 33 | 40 | 39 | 36 | 15 | 25 | 30 | 26 | 31 | 26 |
In terms of productivity, both pairs of Pied Flycatchers were successful in rearing young. The average clutch size for Blue Tit and Great Tit was 9.5 and 8.0 respectively with mean brood size at fledging being 5.9 and 6.7. The complete failure of some half a dozen clutches/broods of tits was probably associated with the very wet weather of late May and early June when nearly four inches of rain fell at the peak of the breeding season.
During the course of this study, one of the parameters used to measure the timing of the breeding season has been the ‘mean first egg date’ - the average, for each species, of when the first egg of each clutch was laid. It has previously been established that the timing of each breeding season is mainly influenced by the severity of the weather in the previous February and perhaps April, and how this can vary from year to year by as much as 10 - 15 days is illustrated in the graph below. However, it is tempting to also interpret the data presented in the graph by suggesting that over the 27 years of this study, the onset of the breading season for all three species is now perhaps a week earlier than what it was in the mid-1970’s! A sign of global warming?
G.W. Follows 26th June 2000
Copyright © Gordon W Follows 2000 E-mail: gordon.w.follows@care4free.net
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