Intra-seasonal changes in directional preferences of Robins (Erithacus rubecula) caught on autumn migration at Bukowo-Kopań ringing Station (N Poland) in 1996
Data were collected in 1996 at Bukowo-Kopań ringing station situated on the southern Baltic coast. During the whole autumn migration period 2380 Robins were caught, and 445 of them were tested with Busse's method for directional behaviour.
Birds' headings were grouped in four main axes: ENE-WSW, NNE-SSW, NNW-SSE and WNW-ESE. The seasonal dynamics of birds caught was divided into periods reflecting waves of migration. For each period the percentage shares of these four main axes were extrapolated into the daily numbers of birds caught. The obtained pattern consisted of four migration dynamics characterising differently heading birds.
The total migration dynamics of the Robin at the station is interpreted as follows. In 1996, the intensive migration started around the middle of September with a numerous wave consisting of at least three populations. The peaks of those population waves were shifted in relation to each other in just 1-2 days, and occurred in following order: birds heading to the Apennine winter-quarter, birds heading to the most eastern wintering grounds, and birds heading to the southern parts of Western winter-quarter. The second, numerous wave consisting at least of birds heading to Mediterranean winter-quarter occurred with a peak on 26 September. In two most numerous October waves around 10 and 18 October, birds heading to the northern parts of Western migration route dominated. However, also birds heading to the Balkan (earlier) or even more eastern (later) wintering grounds formed numerous waves around those dates. The model of Robin migration is proposed, in which the wavy character of migration is generally explained by large-scale factors (like macrosynoptic weather situations, or changes in length of day). Their influence results in the most pronounced waves consisting of populations of different origin. However, the final pattern of dynamics is affected strongly by many other factors: e.g. localisation and characteristics of those populations.
Directional preferences of the Reed Warbler (Acrocephalus scirpaceus) and the Sedge Warbler (A. schoenobaenus) on autumn migration at Lake Drużno (N Poland)
In 2000, during the whole autumn migration period, Reed Warblers (212 indiv.) and Sedge Warblers (205 indiv.) were tested with Busse's method (Busse 1995) for directional behaviour at Lake Drużno ringing site. Distributions of scratches, reflecting cage activity of an individual, were tested for uniformity and more than 97% showed directional behaviour of tested birds. The data were elaborated using non-standard method for evaluation of circular data proposed by Busse and Trocińska (1999) that allows to show multi-modal distributions.
Results show that as much as around 55% of obtained headings point at directions reversed in relation to the normal direction of autumn migration. They suggest that pronounced number of individuals show axial behaviour in the cage. Causes of this phenomenon are still vague and it was decided that directional behaviour will be discussed after reversing northward headings by the doubling the angle method (adding 180°). Then main directions of headings were set as WSW, SSW and SE. They were confronted with available ringing recovery data and quite high (10-12° difference) or even very high (WSW "beam" of migration of Reed Warblers - 5° difference) accordance was found. Using, for the comparison, the same method to the Lesser Whitethroat (Sylvia curruca) data published elsewhere, an excellent agreement between cage data and ringing recoveries at the level 2° only was found. This can be treated as a check of the field and evaluation methods used for basic data presented in the paper. The heading pattern changed in the course of autumn migration and in subsequent periods different headings dominated. The most clear it was for the Reed Warbler data. However, this problem still needs further analyses.
Fat reserves and body mass in some passerines migrating in autumn through the southern Baltic coast
The aim of the present paper is to serve with a huge data set on the fat and body mass of birds that have been caught during the field work of the Operation Baltic since 1983 (earlier data are still not available in a digitalised form). There are given fat score valuations of 38 species and correction factors for the body mass standardisation. Some comments on observed fat scores in species of different migratory habits are added. They should encourage students to continue the research process on a wider scale.
From 1967 until 1990, populations of five Sylvia species migrating through the southwestern coast of the Baltic Sea were considerably low and significantly decreasing in the Blackcap (Sylvia atricapilla), Garden Warbler (S. borin) and Barred Warbler (S. nisoria). While after that period a rapid increase in the populations of these migratory species was noted. Similar changes that had started about 1991 were shown by all five Sylvia species. Such coincidence could indicate some common factors acting upon the studied group of migrants at the same time. Apart from a clear increase in the long-term dynamics of the species observed at Bukowo-Kopań station, the Pearson correlation coefficients of these dynamics calculated for every pair of the analysed Sylvia species in 1967-2006 were high and statistically significant.
Based on the distribution of recoveries of the Lesser Whitethroat (S. curruca) we assumed that the main fraction of birds passing the south-western coast of the Baltic Sea originated from the Scandinavian Peninsula. Recent climate changes observed in this area were consistent with the time when the increase in the number of caught birds was noted. Consequently, we suspect that the analysed Sylvia species passing this part of the coast share vast breeding grounds located mainly on the Fennoscandian Peninsula, where their populations are affected by the same common factors.
Autumn Migration Dynamics and Biometrical Differentiation of the Dunnock (Prunella modularis) Passing the Southern Baltic Coast
The aim of this study is to determine biometrical differentiation among Dunnocks caught at the two ringing sites (Bukowo-Kopań and Mierzeja Wiślana) located on the southern Baltic coast. The distance between those two stations covers 190 km. The material was collected during autumn fieldwork of the Operation Baltic in 1961-2003. The material used for biometrical analysis comprises only immature birds from the period of the most intensive migration, when the numbers of caught individuals allowed to compare the results for both stations. The seasonal dynamics at both sites was pooled for 43 years of catching. Medians of autumn migration for the stations were significantly different. A shift of the median for the eastern site (Mierzeja Wiślana) by 6 days after the median for the western site (Bukowo-Kopań) suggested different origins of birds migrating through the stations. The analysis of standard deviations for the studied biometrical parameters confirms an intra-seasonal change in proportions of birds probably originating from different areas in Europe.
This paper focuses on field practice using different types of orientation cages. The two orientation cage designs most commonly used in field work, i.e. Emlen’s funnel and Busse’s flat orientation cage, are described in detail and compared for compatibility of results, simplicity of use and time effectiveness. Apart from cage designs and field procedures (60-min nocturnal tests in Emlen’s funnel vs. 10-min diurnal tests according to Busse’s procedure), the standard data evaluation procedures are compared and discussed. The data used in the discussion were collected for four species of nocturnal migrants (the Reed Warbler, the Sedge Warbler, the Willow Warbler and the Whitethroat) at the Kalimok Bird Station (Bulgaria): altogether 141 individuals were tested in Emlen’s funnel in 2001 and 788 in Busse’s cage in 2001-2007.
The following conclusions were drawn: (1) Busse’s flat cage design and its standard procedures yield results fully compatible with those obtained using Emlen’s funnel and the associated procedures; this means full compatibility in terms of the directionality of tested birds in the diurnal and nocturnal tests; (2) the procedures compared have distinct differences in terms of constraints on the methods:
– Emlen’s cage is extremely stressful for the bird and should be avoided as much as possible in practice due to animal welfare concerns;
– Emlen’s standard procedure of testing the bird for 60 minutes is completely useless, as this is inefficient in terms of quality of results and causes more stress to the bird than is necessary;
– Busse’s 10-minute standard makes it possible to collect a vast amount of data (12 birds per hour and person) in real field work, even performed in wilderness areas;
(3) At the stage of evaluation of raw data it is essential to use evaluation tools which take into account the fact that raw data items show a high percentage of multimodal distributions, and therefore tools assuming unimodal distribution are unsuitable.
The general migration pattern of passerines can be estimated using a variety of methods. A number of partial analyses based on ringing data, usually limited to a few species, have been published. A very few continent-scale presentations have been offered, as extremely long periods of ringing activity are necessary for passerines. This is especially true for areas where the recovery rate is very low, including vast areas of north-eastern and eastern Europe and the Middle East/Africa. Similarly, radar and moon-watching studies are of limited value for drawing migration patterns within wider areas. Radar studies require good coverage by the radar systems, while weather radar distribution density and the level of evaluation are very uneven. Modern logger and satellite tracking are more applicable to non-passerines, and as yet enable detailed study only of limited numbers of individuals, and not population studies. At the end of the 20th century, a very simple tool was introduced for field studies on the preferred headings of individual birds caught for ringing, i.e. the use of flat orientation cages. This method was introduced as a standard within the SEEN (SE European Bird Migration Network) in 1995. This study presents a preliminary large-scale evaluation of the data collected within this project. The database used contains more than 43,000 orientation tests performed at 45 ringing sites. The area covered stretches from the northern part of western Russia to southern Egypt and from Italy and Poland to Siberia and Armenia. Eight streams of migration are identified within this area, creating a fairly complicated pattern of avian movements.
At the end of the 1980s, a relatively large data set was collected from orientation cage tests of nocturnal migrants caught in one locality in south-western Spain. It was published in The Auk in 1989. At the time of publication, the use of orientation cages was a major advance in detailed studies on passerine migration patterns. The basic evaluation procedure was to calculate the average vector of all numbers representing bird activity in a number of sectors of the full wind-rose and to use the Rayleigh test to determine the statistical significance of the distribution. However, due to hidden assumptions in the procedure used at that time, the resulting heading patterns could be called into question in light of further methodological development. The paper revisits the original set of orientation data collected in the last century in the reported study. The new results from the multimodal distribution accepting procedure are compared with the older pictures and are found to be much better at explaining the migration pattern there. In particular, the Garden Warbler and Reed Warbler, which were claimed to be ‘disoriented’, now show acceptable directionality patterns which do not differ in shape from those of other species.
Due to the presence along the Polish Baltic coast of migratory bird flyways from north-eastern European breeding grounds to wintering areas distributed on continental shelf waters of western and southwestern Europe, the area has been designated as a NATURA 2000 site (PLB 990002). Therefore the site of a planned off-shore wind farm in this area requires monitoring as to its potential influence on birds. This was the first such monitoring performed in Poland. The expanse of water covered by the research included the planned location of the wind farm as well as adjacent areas. A series of 15 investigative cruises were undertaken from the beginning of October to the beginning of May. The period of observations was divided into five seasons: early autumn, late autumn, winter, early spring and late spring. The standard method of counting birds on transects in the form of strips reaching 300 m from the ship was used in the research, as well as the ‘snapshot’ technique (scan with bands transect with snapshot technique). Additional observations were made from a point on the shore.
In the study area maritime birds are present in low or moderate densities, with localized clusters. Two diving benthophagous species dominate: the Long-tailed Duck (58.9%) and the Velvet Scoter (34.3%). The next two commonest species have a share of over 1% within the community – the Common Scoter (3.2%) and the Herring Gull (2.4%). Other species are very uncommon. There is very high fluctuation in the number of birds both observed on the water surface and seen in the air. In the area studied no pronounced migratory passage of waterfowl was observed; the usual migratory flyways probably lie farther to the north and the birds observed in flight perform mainly local movements. Observed bird densities in the study area are considerably lower (52.0 ind./km2) than those estimated for the entire NATURA 2000 area (116.7 ind./km2). In the area of the planned wind farm densities are even lower (36.1 ind./km2, i.e. 31% of the NATURA 2000 level), while densities in neighbouring areas are still below the NATURA 2000 average.
In the subsequent administrative procedure the area was not accepted as the location of the planned wind farm.
Seasonal migration pattern of owls at Bukowo-Kopań station (N Poland) in 2000-2003
Data were collected at the Operation Baltic stations and included over 2000 owls caught and ringed at Bukowo-Kopań station in autumns 2000-2003. Birds were caught with raptor nets, ringed and measured according to the Operation Baltic standards.
The Long-eared Owl (Asio otus) is the most numerous migrant at Polish coast of the Baltic Sea. Migration of this species has wave-like pattern with few nights of very high owl numbers after nights without these birds. Amount of migrants changes decidedly from year to year. This is a result of fluctuations associated with small mammal populations dynamics. Other owl species pass Bukowo-Kopań station in rather low numbers. We can distinguish two groups of owl species according to terms of passage peaks. Both the Short-eared Owl (Asio flammeus) and the Barn Owl (Tyto alba) migrate in the highest numbers generally at the same time as the Long-eared Owl, i.e. at the beginning of November. Correlation is in most cases statistically significant. On the contrary, the migration pattern of the Tengmalm's Owl (Aegolius funereus) is conspicuously different. Passage maximum of this species occurs at the beginning of October and by 25 October the passage is almost finished. But even then individuals that migrate later are caught during the same migration peaks as the Long-eared Owl.
Obtained results indicate that the passage of different owls is similar to the most numerous and typical migrant species - the Long-eared Owl. Other species choose the same nights for passage, which suggests that some common factors influencing owl migration exist.