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Metodhology

The standardised ringing scheme

Since 1980, a standardised ringing scheme is carried out at Falsterbo Bird Observatory (Table 1). The degree of standardisation was chosen to fit in well with the local conditions and the necessary care for the birds as well as to match the demands for comparable data between years. The choice was also based on experience from more than ten years of ringing at Falsterbo by G. Roos and LK.

The work is carried out at two sites. One is the Lighthouse Garden a small stand of mixed trees and bushes (100 x 100 m) surrounding the Falsterbo Lighthouse and situated in an open field area (golf course). The Flommen Reedbed area is situated about 0,6–1,2 km NNE of the Lighthouse. It is an area mainly covered with reeds and sedges, but with some spots of open water and meadows. The use of two sites in different habitats allows a larger number of species to be monitored.

Table 1. The standardised ringing scheme at Falsterbo Bird Observatory.
Site From To     Days Hours/Day Net
Lighthouse garden (spring) March 21st June 10th 82 4 max 21
Lighthouse garden (autumn) July 21st November 10th 113 6 max 21
Flommen, reedbed (autumn) July 21st September 30th 72 6 max 20

Only mist-nets (9 m length and mesh size 16 mm) are used. Depending on weather conditions the daily number of nets used is varying. At the most 21 nets are used at the Lighthouse and 20 at Flommen. The work is carried out seven days a week, weather permitting. For the care of the birds no trapping efforts are carried out on days with rain or strong wind.

The nets are put up before dawn and then controlled every half hour. The daily trapping period lasts at least a minimum 4 (spring) or 6 (autumn) hours at each site and continues thereafter as long as the number of captured birds exceeds ten individuals per hour. Then the nets are removed from the poles.

Numbers

Up to and including 2007, 627 965 birds were ringed within the standardised scheme. Almost two thirds of the total are birds ringed at the Lighthouse during autumns, while only 17% were ringed during springs. The remaining 19% were ringed at Flommen.

Graphs etc. are based on number of ringed birds per species, season and site. The numbers show the number of ringed or reringed birds, while controls of birds ringed elsewhere are not included.

Local birds are included in the totals. In most cases they represent a very small part of the total numbers. However, in some fairly resident species like House Sparrow, the proportion of local or regional birds may be larger.

Statistic tests are performed using Spearman's Rank Correlation.

Influence of topography and weather

The use of the figures presented here in a correct way demands knowledge of the special conditions at Falsterbo. The geographic location on the south-westernmost point of the Scandinavian peninsula in combination with the major direction of bird migration in autumn being towards south-west lead to a high concentration of birds during autumn migration. In spring the northward migration is not at all concentrated to Falsterbo. On special occasions, usually caused by periods of cold weather, however, rather strong reverse movements (towards SW) are observed. The effect of leading lines makes the numbers of birds on reverse migration larger than those on "regular" spring migration. The high spring totals in species like Dunnock, Song Thrush, Redwing and Chaffinch during the mid-1980s are all mainly effects of reverse migration caused by changes to cold weather.

If the same pattern is valid also in nocturnal migrants is not known, but our personal experience of 28 spring seasons with standardised trapping is, that large numbers of grounded birds often occur in connection with "bad" weather, i.e. a front zone between cold weather in the north and warm in the south. Flycatchers, for example, are caught in large numbers only under such conditions. Thus, spring captures at Falsterbo are more irregular than autumn captures, which may be an explanation why relatively few correlations were found between spring and autumn totals. Certainly there are influences of weather also in autumn, but at Falsterbo these seem less crucial for the seasonal ringing totals than in spring, except for some quite rare and extreme situations. In a long-term perspective, however, the effect of extreme weather situations will by definition be evened out.

Therefore, it is safer to rely on autumn totals than on spring totals for monitoring purposes. Furthermore, autumn totals are on average larger than spring totals.

Spring totals, however, as well as autumn totals, are very useful for phenological studies.

Selections for the web presentation

A minimum of 50 individuals per season and site was set as a condition for a graph to be shown. This condition can easily be adjusted if necessary. However, this means that a number of species with small samples happens to be included, but some of them show interesting tendencies all the same. For each species the the season/site preferred for monitoring is indicated. In relevant cases, statistcal tests are shown and furthermore, comments on the results are shown.

All numbers, graphs, statistics etc. are automatically updated at every turn of the year.

2021-09-17
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