ALBERT

Description / Table of Contents: Summary Two different cages are used for orientation tests:Emlen funnels andMerkel-Wiltschko-cages. Most of the orientation tests with migrating birds were performed inMerkel-Wiltschko-cages. In this paper I analyzed the activity behaviour of Blackcaps, Lesser Whitethroats and Robins at orientation tests inMerkel-Wiltschko-cages during autumn and spring migration. The orientation behaviour of these night-migrating birds was tested with reference to the dependence on different magnetic field conditions and on an artificial starry sky. The following results were obtained: 1. Blackcaps and Robins are able to get orientational information from the local geomagnetic field, but Lesser Whitethroats are totally disorientated in this test condition. 2. When magnetic N was turned by 180° to geographic S by reversing the horizontal component of the earth magnetic field Blackcaps changed their directional preferences according to this magnetic field. 3. When the horizontal and vertical components of the magnetic field were reversed they had a mean direction which is equivalent to that in the normal earth field. 4. In a partly compensated magnetic field which could not be used for orientation no significant directional preference was found. 5. In an artificial earth magnetic field and with artificial stars robins are able to obtain orientational information by the magnetic field and by star patterns. — The analysis of the orientation behaviour in theMerkel-Wiltschko-cage showes that it is impossible to point out a correlation between activity, the vector length and the amount of circling in the test condition in the geomagnetic field. But in test conditions with artificial magnetic fields there were strong correlations. The birds reacted on these artifical magnetic fields with a higher activity and a higher amount of circlings but the plotting of the night migration direction was not influenced. I interpret this behaviour as a stress reaction on these artifical magnetic fields produced by Helmholtzcoils. The distribution of the headings of the single test night was more concentrated during autumn than during spring migration. But in the single test night the vector length of the mean direction was higher during spring than during autumn migration. An interpretation of these facts may be given by the glacial periods or by the food shortage at wintertime. Therefore in autumn the birds had to fly by the straightest way to their winter ground. At spring they can remove behind the receding winter. The analysis of the orientation data obtained in spring migration revealed a strong correlation between orientation behaviour, temperature and pressure. The analysis showes that theMerkel-Wiltschko-cage is a very good orientation cage to test birds which live in bushes. In this test cage the birds keep up their normal migratory behaviour. An other advantage is that single external factors can be tested under laboratory conditions in this cage.

Description / Table of Contents: Summary From 1970–1972 number of bird species and individuals were determined for an agriculturally used coastal area of the North Sea (59 % grassland, 38 % arable land) of 96.14 hectares (54.11 N/9.03 E). The average number of species was 30.9 (May/January = 3.8). The number of breeding species varied less than that of visitors and migrants. In the course of the year the number of species reached two peaks: May, and to a lesser extent, October. The yearly spectrum of species consisted of 32 % breeding birds and of 68 % non-breeders. This high proportion of non-breeding species can be explained by local conditions: breeders of the surrounding area feed in the marsh. The average density was 66.3 ind/10 ha (August/January in normal winter = 14.9). In a cold winter the quotient was much higher. The proportion of non-breeding birds can reach 100 %. The average yearly population of breeding species (33 %) varied less than that of the non-breeders (67 %). The oscillation showed two peaks as well: one in March/April and a higher one in August. In August the number of individuals was extremely high. Insectivores, herbivores and omnivores found favourable feeding conditions. On a yearly average 62 ind./10 ha could be found on grassland and 38 ind./ha on arable land (details see fig. 8). The diversity varied between 1.08 (February) and 2.55 (September). Comparisons indicate similar values in other parts of Central Europe.

Description / Table of Contents: Zusammenfassung Beim Einfarbstar wird die Lauffärbung mit zunehmendem Alter heller und kann als Hilfe bei der ungefähren Altersgruppierung adulter Vögel verwendet werden. Die Pneumatisation des Schädeldachs dauert etwa 6 Monate (Juli bis Dezember bei Jungen aus Erstbruten, August bis Januar bei Jungen aus Zweitbruten). Nach dem Stand der Pneumatisation des Schädeldachs lassen sich juv. und ad. am besten im Oktober und November unterscheiden.

Description / Table of Contents: Summary Wintering strategies of a partially migratory population of European blackbirds in southwestern Germany were studied (1) to determine the relationship of the resident or migratory behaviour to age and sex and (2) to assess the relative fitness of resident and migratory individuals by determining structure of the breeding population, start of egglaying and breeding success. There was no difference in the tendency to migrate between male and female first year birds. Only in males the migratory group consisted of more first year than older birds than the resident group. With increasing age females tended to migrate, while males tended to winter in the breeding area. Few birds changed from resident to migratory status in successive years. The rate of reproduction in resident males was greater than in migratory males because of greater success in establishing territories, earlier start of egglaying, better quality of the territory and higher nesting success. Resident and migratory females were represented in equal numbers in the breeding population. Equal numbers of migrant and resident females were paired to resident males and their breeding success was independent of their status and depended only on the status of the male. Therefore there appear to be less disadvantages of migratory behaviour in terms of reproductive output in females. These differences in fitness of migratory and resident birds are consistent with the hypothesis, that there is a balanced polymorphism of these two wintering strategies in partialy migratory populations, which is balanced by differential productivity and mortality.

Description / Table of Contents: Summary During a five-year study of hole-nesters in Schlüchtern, Hessia, FRG (50° 21′ N 09° 31′ E), it was found that Great, Blue and Marsh Tits(Parus major, P. caeruleus, P. palustris), Pied Flycatchers(Ficedula hypoleuca), and Nuthatches(Sitta europaea) interrupt their normal egg-laying for one or more days after a drop in temperature. For Great and Blue Tits interruptions during egg-laying could be found in all five years of the study. The interruptions were observed in every stage of the laying sequence but they were significantly more common after the laying of the first eggs than in later stages. Except for 1977, laying interruptions could be observed during the entire laying period. After longer periods of cold weather (average daily temperatures between 0 and 5 °C), Great and Blue Tits show interruptions in the laying sequence from 8 to 10 days. In years when a high percentage of individuals showed laying interruptions, the interruption intervals were longer. In most cases egg-laying was not stopped immediately following a drop in temperature but after a delay of 2 to 4 days. On the average, 37% of Blue Tits and 23% of Great Tits interrupt their normal laying sequence. The stronger reaction of the Blue Tit could be explained by a lower resistance to drops in temperature (cf. the more restricted range of the Blue Tit which does not extend to higher latitudes and altitudes). No differences could be found between one year old and older Great and Blue Tits in their tendency to interrupt egg-laying. Great and Blue Tits which interrupt their egg-laying did not differ in body-weight from individuals which did not. No differences in clutch size between clutches with and without laying interruptions could be found. The eggs laid by Great Tits after an interruption are larger than the eggs laid prior to an interruption. In Blue Tits no difference could be observed. The prolonged laying period of clutches with laying interruptions did not influence hatching success. It is suggested that interruptions during egg-laying in Great and Blue Tits make it possible to colonize areas with bad weather and poor food conditions during the egg-laying period.

Description / Table of Contents: Summary Caused by severe winters in 1961–1963 the Bavarian breeding population break down to 250 breeding pairs. The population increased again to 400–500 breeding pairs in the following decade, but in 1972 the herons must be protected because of continuing decrease. In 1979 the population recovered to 1170 breeding pairs distributed in more than 70 colonies. Carrying capacity for Bavaria is 1300–1500 breeding pairs. Since 1981 the heron is pursued again in the surroundings of fish farms. Before protected, the rate of growth of the Bavarian breeding population was 0.008. Therefore the population could not compensate breakdowns by severe winters in sufficient time. The intrinsic rate of natural increase, rmax, is 0.222. The population increases with this rate from 1974–1977. In increasing heron populations the average colony size increases as well. This is due to the growth of bigger colonies. In contrary, small colonies are relatively constant in number and size. Therefore there is no possibility of population growth and survival in populations too small and splitted. The average colony size is a measure for the environmental quality for the heron in a region. The herons changed the roosting habitats due to the reinsertion of hunting. Heron numbers in fish farms depend mainly on the availability of fish prey and only weak on shooting or deterring. There is no indication, that fish harvests have increased due to heron hunting. The kill of the herons involved decreasing numbers of breeding pairs in parts of Bavaria and retarded the compensation of decreases due to the winter 1980/81. Small isolated populations will disappear soon. Heavily influenced may be small foreign populations like the Hessian one passing through Bavaria in autumn. Danger of extinction exists also for Purple Heron, Night Heron and Bittern in Bavaria. If the heron hunting will be proceeded, a controll of hunting success must be established and the herons should be used in a bioindicator programm.

Description / Table of Contents: Summary In a three year study of the breeding biology of hole nesting passerines in two study areas in the center of Frankfurt (city areas FGW and ZOO) were compared with two study areas in the countryside near Schlüchtern (BRE and PAW). In the city only Great Tit and Blue Tit were found, whereas in the countryside also Marsh Tit, Coal Tit, and Pied Flycatcher. The breeding density of Great and Blue Tits varied considerably; one of the city areas (FGW) showed the highest, the other (ZOO) the lowest density. We found no evidence for regulation of numbers by interspecific competition between Blue and Great Tits. However, there was a strong intraspecific competition. In both Blue and Great Tits many one year old males did not breed. The mortality of adult female Great Tits in one of the city areas was lower than in the countryside in one of three years. The other years revealed no difference. The clutch size differed significantly between the city and the countryside. The mean clutch size in FGW was 7,6 and in ZOO 7,7, whereas in BRE and PAW clutch sizes were 9,2 and 9,3 respectively. Hatching success was rather high in all study areas (72–86 %). Fledging success, however, varied considerably. In the city areas only 68 % (FGW) and 34 % (ZOO) of the Great Tit nestlings fledged, whereas in the countryside fledging success varied from 81 % (PAW) to 88 % (BRE). The weight of nestling Great Tits was significantly lower in the city than in the countryside area PAW. The study shows that Great Tits may cope with urban habitats if they can find a refuge (like FGW) from which population surplus can immigrate into less suited habitats (like ZOO).