The Berkshire Kingfisher Survey 2005

15 December 2005 | Chris Robinson

Background to the survey

The distribution of Kingfishers Alcedo Atthis in Berkshire has not been examined in detail since the survey work for the Birds of Berkshire (Standley et al) which was carried out during the years 1987-1989. This had revealed 81 confirmed breeding or probably breeding pairs across the county, a figure which the authors suspected may have been an under-estimate, largely due to the paucity of confirmed breeding records from central Berkshire. One aim of this survey was therefore to attempt a more accurate estimate, as well as bring our knowledge of the species' distribution up to date. The other was to encourage as many birdwatchers as possible to get involved in some simple survey work. There must be very few people who are unable to recognise the electric blue flash of the Kingfisher as it streaks downriver or across a lake, so it was felt that this would be an ideal survey species for both beginner and expert alike. As the bird is so easily recognisable, it was also thought that there would be very little risk to data integrity if we engaged ordinary members of the public in the recording process while at the same time this would gain valuable publicity for the co-sponsors of the survey, the Newbury District and the Reading Ornithological Clubs. This was obtained through the local press and several newspapers were kind enough to print articles about the survey which attracted a good deal of interest as well as some useful records. There was also good publicity given via both bird clubs' websites as well as the widely read berksbirds website.

Methodology

In lowland UK, the Kingfisher tends to be more or less sedentary with parent birds normally remaining within their breeding range throughout the year and the young dispersing only short distances from it after fledging. Longer distance migration does occur but this is normally brought on by the onset of freezing weather. With British winters becoming milder it was felt that movement of birds within Berkshire was likely to be slight so the survey could be started in January in order to maximise the observation period and increase the number of sightings. Preparation for breeding has usually started by early April and the first eggs are laid towards the end of the month. With an incubation period of 20-21 days and a fledging period of nearly four weeks, this means that the first young will be on the wing from mid-June onwards. A second brood may be raised following this. The cutoff date for the survey was therefore chosen as the end of July, a date selected to provide a long enough period to record most breeding attempts while (hopefully!) not confusing our counts too much with fledged or dispersing young. Observers were asked to simply record the date and location of any sightings and make notes on activity or interesting behaviour if these were observed.

Results

Records were received from three sources:

  1. Paper or email sent in to the survey organisers in response to our publicity
  2. Records downloaded from the 'Sightings' page of the berksbirds website
  3. Records submitted to the Berkshire Bird Bulletin

Some of these were duplicate (or even triplicate!) so the data had to be manually edited in order to eliminate these. This resulted in a total of 543 unique records, approximately half of which came from the first source with the remainder from the other two. These data were then entered into a MapMateŽ database for analysis and production of distribution maps As well as straightforward number reporting a number of observers gave detailed or background information on what they saw and we are very grateful to all those who took the time and trouble to send in records for this survey. There is a section at the end of this report which summarises some of the extra-survey material.

Analysis

Although some records supplied sufficient information to enable confirmation of breeding (e.g: a bird seen entering nest hole; carrying food or, later in the season, the recording of juvenile birds), most did not. With a primary purpose of the survey being to establish the number of breeding pairs in the county, we therefore had to rely on interpretive methods in order to estimate the location and number of breeding territories. Firstly, all the records were examined and, if not already supplied, a grid reference was added. Usually this was a 4-figure one (i.e: to an accuracy of 1km), although occasionally enough detail was given to get a greater precision. As the intention was to plot the distribution of all sightings to the 1km square level, 6-figure precision was not essential but did sometimes prove useful in segregating adjacent territories. A few supplied references had to be corrected, the normal error being a confusion between "eastings" and "northings", resulting in apparent sightings in mid-Oxfordshire, Hampshire or even further afield! We had originally suggested that observers could submit records from just over the county border as it was felt that they might be useful in identifying Kingfisher territories which spanned a border (birds, after all, are no respecters of these!). In the end, with the small exception of Dorney Wetlands there were very few of these so they were not included in the final analysis. Once all records were complete and correct they were imported into MapMateŽ. This allowed analysis and plotting of Kingfisher distribution across the county using a number of different criteria, such as date, site, etc. Figure 1 shows the distribution, plotted by 1km square, of all Kingfisher records over the whole survey period. This shows a total of 152 squares which recorded at least one sighting during the survey period. This does not of course mean that there was this number of Kingfisher territories or even, necessarily, this number of Kingfishers in the county. In fact, given the long time period which the map spans one might expect it to better plot the distribution of water bodies and water courses within the county; which indeed it does rather well! It does serve one function however in that it reveals an apparent shortage of birds in a few places, notably the upper reaches of the R. Lambourn, the R. Pang and parts of the R. Loddon, with some possible blank areas on certain parts of the R.Thames and R. Kennet. It seems likely that the explanation for at least the first three might be more to do with lack of observer coverage rather than lack of birds, although some roughly similar observations were made in the Berks Atlas.

Berkshire map showing distribution of all Kingfisher records by 1km square
Figure 1. Distribution of all Kingfisher records by 1km square

With the benefit of hindsight, it may have been better if we had plotted incoming records as they came in so that we could identify any potential "blank spots" and arrange extra coverage of these areas. We did in fact ask people to tell us where they did not find Kingfishers as well as where they did but, perhaps not surprisingly, we received very few such records. In any case many people held on to their records until the end of the survey period so this "map-as-you-go" method may not have been that productive. While the preceding map shows the absolute maximum distribution (with one or two possible exceptions, as already discussed), 152 breeding pairs is certain to be an overestimate. The main reason for this is that the map does not differentiate between winter and breeding period records so, given that there is some extra winter mobility in this species, many of the plotted squares will represent winter-only records. In order to refine the estimate, the complete dataset was first analysed by inspection of each record in order to establish the true or likely status of each 1km square with respect to Kingfisher breeding usage. This was done using one of four criteria:-

  1. Squares with proven nesting (e.g: nest found or young seen by observer)
  2. Squares with a probable nesting or breeding attempt (e.g: bird carrying food)
  3. Squares with a possible breeding attempt (e.g: pair seen in breeding period)
  4. Squares occupied during both winter and spring/summer periods

The last method is perhaps a little controversial, but as there were relatively few records in the first three categories, it was hoped that this could provide a reliable alternative to the more traditional ones. In reality, this only generated 62 probably breeding birds, a figure which is almost certainly too low. There are at least a couple of probable explanations for this:-

  1. The survey method, being basically non-structured, did not guarantee that all squares would be visited regularly or throughout the survey period. One just has to look at the dataset from a geographic perspective to see the variations in coverage; for example nineteen records from R. Thames at Remenham versus just six for the whole of the R. Pang!
  2. Reduced surveyor activity during the winter months of the year, particularly in the more remote locations. A 13% increase in spring/summer records over winter ones would appear not to support this theory but see next!
  3. Reduced observability of Kingfishers during the main breeding months. Records for April, May and June were all significantly lower than any of the three preceding months and only exceeded them in July when first broods would have been raised and young would be on the wing.

This method having failed to come up with a credible result it was time then to turn to an alternative analysis!

Figure 2 below shows the distribution of Kingfishers by 1km square for the three winter months (January through March), a total of 90 squares in all. 1km is probably not enough to separate individual birds, especially in the non-breeding season as they are likely to be much more mobile, but inspection shows that most squares are not adjacent so this figure could be close to the total number of birds holding winter territories.

Berkshire map showing distribution of winter Kingfisher sightings by 1km square
Figure 2. Distribution of winter Kingfisher sightings by 1km square

Next the distribution of spring and summer sightings (April through July) was plotted, see Figure 3 below. This yielded a total of 111 occupied squares during the period April to the end of July.

Berkshire map showing distribution of spring/summer Kingfisher sightings by 1km square
Figure 3. Distribution of spring/summer Kingfisher sightings by 1km square

The presumption was that the preceding map should represent the distribution (and number) of breeding pairs in the county but in light of previous comments about the jump in sightings during July, it was felt safer to eliminate these from the map. This amended "main breeding season" distribution is shown below.

Berkshire map showing distribution of 'breeding season' Kingfisher sightings by 1km square
Figure 4. Distribution of "breeding season" Kingfisher sightings by 1km square

This shows a total of 89 1km squares occupied during the months of April through June (the main breeding period), a figure remarkably close to that for the winter months. Examination of the winter and spring distributions from a geographical perspective reveal an almost complete absence of spring records from the main gravel pits, such as Theale, Wraysbury and Dinton Pastures, the likely reason being that these sites, while being good for winter feeding do not have appropriate habitat for breeding (i.e: good nesting banks) and birds therefore settle in sites which do. Presumably the same sorts of minor migration take place at the beginning of each breeding season in other, less obvious, locations too. This being the case, it seems a reasonable conclusion that the closely matching numbers of Kingfishers for winter and what I have called the "main breeding season" are in fact no coincidence and the two maps simply reflect the redistribution of the same birds.

The map below shows pictorially the difference between winter and "breeding season" distribution. The blue squares are those occupied only in the winter months; the green are those occupied in the breeding season. The locations of our main gravel pits stand out; although the blank in the Hungerford area is less explicable...

Berkshire map showing the difference between winter and 'breeding season' distribution

Conclusion

After allowances have been made for records from adjacent squares (which can represent just a single bird) there would appear to have been a minimum of 78 occupied territories recorded during this survey. There could be at least another 6 areas which might have held breeding birds but which failed to yield any breeding season records.

The probable number of breeding Kingfishers in Berkshire 2005 was between 78 and 84

Footnotes

I thought you might be interested in this photo. I was sitting out on the patio the other evening when I heard a thud against the window. Unfortunately the bird that had dazed itself was a kingfisher. I sat with it cupped in my hand to keep warm for 20 minutes and was so grateful it made a full recovery before flying away. A happy ending and I was grateful to get a photo of this most beautiful bird before he left.

Kingfisher