30A SITE FIDELITY AND LOCAL MOVEMENT OF BIRDS WITHIN THE WOOLSTON EYES RESERVE 2010

by David Norman and Michael Miles

In the British ringing scheme, movements of ringed birds more than 5km (for most species) are dealt with nationally, and these are included every year in the ringing report. But records of movements shorter than 5km are left to be treated locally, if at all. The steady and long-term programme of ringing at Woolston affords a great opportunity to examine the site-faithfulness, or otherwise, of some species.

 

We have analysed the records for all the birds ringed or retrapped at Woolston in the eight years 2003 - 2010 inclusive on No.1 and No.3 Beds, including in the latter category those in the centre and at the southeast corner of No.3 Bed. The main ringing areas at No.1 and No.3 Beds are 2.3km apart. The word 'retrap' is the standard ringers' vocabulary although all of those birds were caught in mist-nets.

The following Table shows the results for all those species of which at least 100 individuals have been ringed in this period.

 

                                                         Total                  Total                  %                   Total                    %

                                                      Ringed                Retrapped           Retrapped        Retrapped             Retrapped

                                                      2003-2010          Same bed            Same bed        Different bed         Different bed

Great Spotted Woodpecker                     124                    63                     50.8                  3                       2.4

Sand Martin                                          398                      3                       0.8                  0                         0

Swallow                                              2882                   10                       0.3                  4                       0.1

Wren                                                  1608                  382                     23.8                  0                         0

Dunnock                                               837                  277                     33.1                  0                         0

Robin                                                 1348                  401                     29.7                  4                       0.3

Blackbird                                              749                  156                     20.8                   0                         0

Song Thrush                                         364                   53                      14.6                  1                       0.3            

Sedge Warbler                                       982                 104                     10.6                   1                       0.1            

Reed Warbler                                       4346                 775                     17.8                 42                       1.0

Whitethroat                                         1154                  136                     11.8                  1                       0.1

Garden Warbler                                     281                    17                       6.0                  1                       0.4

Blackcap                                              3632                 342                       9.4                 13                       0.4

Chiffchaff                                            3078                  500                     16.2                 18                       0.6

Willow Warbler                                    1735                  298                     17.2                   5                       0.3

Goldcrest                                              714                  108                     15.1                  0                          0

Long-tailed Tit                                     1221                  546                     44.7                  3                        0.2

Willow Tit                                             249                  146                     58.6                   6                       2.4

Blue Tit                                               2031                  824                     40.6                   4                       0.2

Great Tit                                             2075                  984                     47.4                   9                       0.4

Jay                                                       115                   25                      21.7                  0                          0

Chaffinch                                             1898                 316                     16.6                    5                      0.3

Brambling                                             133                     5                       3.8                    2                      1.5

Greenfinch                                           5939                 742                     12.5                 130                     2.2

Goldfinch                                              197                    14                      7.1                    0                         0

Linnet                                                   335                     7                       2.1                    0                        0

Lesser Redpoll                                       662                    23                      3.5                    2                      0.3

Bullfinch                                               968                   416                    43.0                  14                      1.4

Reed Bunting                                       1623                  392                     24.2                  25                      1.5

Totals                                             41678                8065                   19.4                290                      0.7

 

Recaptures on the same bed.

The results show that, on average, almost one-fifth of the individuals are caught again on the same bed. This proportion varies enormously between species, from over half for Willow Tit and Great Spotted Woodpecker, and more than 40% for Bullfinch, Long-tailed Tit, Blue Tit and Great Tit, to an average of 14% for the warblers and less than 1% for the roosting hirundines (Sand Martin and Swallow). In general the resident species, and especially those attracted to the feeding stations, have higher retrap rates than the migrants.

 

However, many individuals within the 'resident' species can move considerable distances, as shown for instance with Greenfinch and Reed Bunting in the annual ringing reports. In some others there may be a high proportion of continental immigrants augmented in winter by visitors mainly from Scandinavia.

 

Our analysis, so far, has not considered the age of the bird or whether it was retrapped within the same or a subsquent season.

 

Movements between No.1 and No.3 Beds

The overwhelming picture is of site-faithfulness, with, averaged over all these species, birds some 28 times more likely to be retrapped on the bed where they were ringed than to have moved between these two beds. There are substantial differencies between species, however. It may not be surprising that no Wren or Dunnock, with their reputation as the most sedentary of species, has moved the 2.3km between these sites. But no Blackbirds have made the same swap, either local birds or continental immigrants, and only one Song Thrush, a juvenile ringed on No.1 Bed on 18th September 2009, caught on No.3 Bed just over two weeks later (4th October 2009). All four of the Robins that switched beds were ringed as juveniles in spotty plumage then caught on the other bed in August - October of their first year, and this is probably the extent of normal post-juvenile dispersal.

 

Perhaps it is significant that the two species with the highest of all retrap rates, Great Spotted Woodpecker and Willow Tit, also show the highest rate of movement between the beds at one-in-forty of those ringed. The sample size is small, however, only three and six birds respectively that moved beds, compared to 63 and 146 that were retrapped on the same bed where they were ringed.

 

The Greenfinch provides the most numerous examples of inter-bed movement, and this species is less than six times more likely to be recaught on the same site (742 birds) than having switched to the other bed (130). Some of the inter-bed movements are quick, and there are two records of Greenfinches being caught on the two beds only three or four hours apart. Greenfinch TK14068 was ringed on 21st October 2006 at 08:30 on No.1 Bed and retrapped at 12:00 the same day on No.3 Bed, whilst Greenfinch TJ08434 made theopposite journey, being ringed on 27th December 2008 at 11:00 on No.3 Bed and retrapped at 14:00 the same day on No.1 Bed.

 

Two of the roaming Long-tailed Tits were probably paired, or atleast part of the same flock, having been ringed together on No.1 Bed on 7th October 2005 and later caught together on No.3 Bed on 21st January 2007; one of them had also been caught on No.2 Bed on 29th April 2006. It seems especially odd that birds that travel several thousand km to reach Woolston, such as warblers, do not then move around more when they reach the Reserve. But only Reed Warbler has as many as 1% of the birds handled on both beds, and there is only one example each in the last eight years of Sedge Warbler, Whitethroat and Garden Warbler.

 

A similar effect is seen with Lesser Redpoll, which is mostly found as a passage bird, sometimes in large flocks, with 662 birds being ringed in these eight years. Only 16 of those were ringed at Woolston in the May - August period yet it is two of those, probably local birds, that have moved between beds, and none of those from the passage flocks. This was the pair of adults apparently just having finished breeding, caught and ringed together in the southeast corner of No.3 Bed on 1st August 2005 and retrapped together on No.1 five days later.

 

How do birds cross the Thelwall Viaduct?

For those birds that do move between No.1 and No.3 Beds, we wonder do they cross over or under the M6?

There is another ringing site in Warrington run by fellow MRG member Phil Guest in Gorse Covert on the north-east edge of the town. This site is just 4km due north of No.1 Bed and 5km from No.3 Bed at a heading about 15 degrees east of north. A bird leaving No.1 Bed flies over open countryside to Gorse Covert whereas a bird leaving No.3 Bed travels first over part of the Eyes, then the edge of Woolston village and finally over Risley Moss and the M6 motorway. In a period from 2003 to 2010 there were 19 Greenfinches ringed at Woolston and subsequently retrapped at Gorse Covert. Of these 16 were ringed on No.1 Bed and just three on No.3 Bed. After adjusting for the different number of Greenfinches ringed on the two beds (17% more birds were ringed on No.1 Bed than No.3 Bed) it appears that a Greenfinch ringed on No.1 Bed is four and a half times more likely to travel to Gorse Covert than one ringed on No.3 Bed. Movements in the opposite direction show an even larger variation. Of 15 Greenfinches ringed at Gorse Covert and later retrapped at Woolston, 14 of them were caught on No.1 Bed and just a single bird on No.3 Bed.

 

This variation is very unlikely to have happened by chance; statistically the probability is much less than one-in-fifty-thousand. It follows that there is an external factor influencing the behaviour of these birds. Some possibilities might include;

Distance; it seems unlikely that differences between a flight of 4km and one of 5km would account for this disparity.

Heading; there is no obvious reason why a difference of 15 degrees in heading would influence the bird's direction of travel.

Topography; the most likely explanation for this difference is topography including the 'barrier' of the M6 motorway. Birds leaving Gorse Covert appear to be flying south parallel with the M6 with a similar influence on birds heading north from No.1 Bed. There is no clear 'exit route' from No.3 Bed that does not involve flying over a residential area and it seems unlikely that Greenfinches would be averse to doing so given that they are a common bird of built up areas and gardens. Although we now enter the realms of speculation, it may follow that it is the M6 motorway itself that acts as a barrier to birds moving between No.3 Bed and Gorse Covert.

 

Finally we return to the question posed above and ask "if Greenfinches are averse to crossing the M6 how come 130 inter-bed movements have been recorded in the study period?" The answer might be that Greenfinches can move quite easily between beds whilst staying in or close to the trees and shrubs available and pass under the Thewall Viaduct and M6. There is a project opportunity for someone to study the interaction between Woolston's birds and the landmark structure that divides the Reserve.

 

David Norman and Michael Miles 

 

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