Methods used to study birds migration

We studied the bird migration aspects based on the methodical complex that was elaborated earlier. We have been amending this system according to equipment development. This complex includes 11 basic methods: visual-optical ( day's ), acoustic-optical (night's) monitoring, the catch of birds and lifelong analysis, collecting model species, air-visual, automobile (boat) and foot registrations, birds calculation in the concentration areas, transit-flight flocks registration, electronic processing and data analysis. As we have already discussed this complex in the periodical press we will focus only on the main aspects.

Visual and acoustic-optical monitoring. To study day's migration we based on the methods elaborated by E.I Gavrilov, M.N Yablonkevich, D.F Liuleeva (168), though we slightly modified them and that helped us to register birds' flight within the whole range of heights. We carried out optical monitoring using the binoculars of 7-8 and 20-30fold magnification, but unlike the method mentioned above, they were set not in upright position but at angles 20-30' and that required the insertion of extra algorithms into the calculation data. Nevertheless, owing to the extension of observation area (ellipse), monitoring process became more effective. We also modified the general monitoring system: we had been registering birds daily for 120-minutes at once ( 30 minutes for each method) with the interval of 2 hours.

In the process of visual monitoring the width of registration zone was being changed according the distance of birds detection (the same as in the standard method). That is why we differentiated the birds according to the height: large birds-1000m, medium birds-200 m, small birds- 50 m. During optical monitoring we registered all birds. The flight direction of each species and flock was detected in degrees according to the magnetic azimuths; during optical monitoring- according to imaginary clock points.

Birds that migrate by dense groups ( for example geese, ducks, some sandpipers) in the height up to 1000 m are rarely got in the field of vision and this phenomena causes birds' undercalculation. Undoubtedly, in this case it is more useful to carry out visual monitoring. On the contrary, the possibilities of the visual monitoring are limited at the height of 1000 m and up, though the effectiveness of optical observations increases due to the registration area expansion. The combination of methods makes it possible to use advantages of both visual and optical observations. In the majority of monitoring areas, it was enough to use binoculars of 7-10-fold magnification to register day's birds' flight. In order to conduct selective surveillance measures on high altitude migration, binoculars of higher magnification but with the lower visual angle were used.

We used night's monitoring optical method that was adjusted in accordance with enough elaborated variant of "moon"method (12). At first we used telescopes of 40-fold magnification, afterwards-binoculars of 30-fold magnification, that simplified the birds' detection by their silhouettes. The acoustic method, mainly known as the registration of transit birds' voices, was carried out in synchronously with the "moon" method. To record birds' voices we used special microphones, such as ECM-HS1, installed in digital video-cameras. In other aspects the technique of the"moon" monitoring fitted conventional methods.

Most of cases of visual-optical monitoring method were entailed by catching migratory birds by means of different traps and cobweb nets, registering routes and indicating the birds presence in the concentration areas. This activities were of vital importance during defining the number of birds in the group or individual species. In order to monitor the species of night migratory birds we had been tracking their movements in the time before dawn and with the help of binoculars we had been identifying all cases of birds' landing.

The catch and birds' marking.
We used 2-3 type s of portable traps as well as shuttered nets (25-40 items) for birds' catch in order to carry out complex studies in the stationary conditions. We applied 2 main traps (portable and "swallow") and one extra, that was used for birds' catching in the sparrow's overnight stops territory. The are a lot of advantages of this elaborated traps, one of the main is that their size is smaller and its' original cut out makes it possible to set without tough frame manufacture.(114). On the whole this traps are as effective as stationary ones (Rybachinskii, Kazahstanskii).

In order to obtain numerical characteristics of web net collection we proceeded from the rate of birds' catch. Due to the fact that large sandpipers were caught 4-4,6 times rarely we proportionally increased the total area of large-sell nets "daradan".( table 1). In our investigation of birds we used the methods elaborated by V.R. Dolnik (32), N.V. Vinogradova .

The electronic processing of data. The basic scheme of preliminary electronic calculation is shown in the table 2. We calculated the height of birds' flight according to the formulas: the relation of birds' size to ruler scale placed in binoculars ocular during day's monitoring; the relation of visual silhouette size to the crater " Plato" diameter during night monitoring (12; 113)

The mathematical principles of direction detection and formulas for calculation are listed in a number of written research works (175; 181; 182; 186), we based on the formula of S. Rens. The calculation of body orientation was carried out only in the cases when that was possible to determine. We estimated the night flight direction when the angles of moon rise above the horizon were more than 14 (180). In the process of flight density calculation the width of registration zone is rather significant, because it is a variable that depends on distance, birds' flight direction and incline angle of the optical device. Some researchers didn't follow this rule and the height allocation was denoted not precisely. (175; 179; 180; 183). Our calculation method is close to K.V. Bolshakov's (9-12), we also grade all space and time limits of the method.