Demography of grey partridges Perdix perdix in Poland in the years 1991–2004: reasons of population decline

Grey partridge Perdix perdix populations were monitored in the years 1991–2004 in ten agricultural areas (100–200 km² each) located in various regions of Poland. Spring density (call counts in March/April) and parameters describing reproductive success (counts of adult and young birds in coveys found in August) were estimated, and annual survival rate of adult birds was calculated. In the 1990s, the mean spring density of grey partridge in Poland showed a threefold decrease. In 1993 (the year of the highest mean density), from 4.6 pairs/km² to 20.0 pairs/km² were found in individual areas; whereas in 2004, there were from 0.4 pairs/km² to 8.3 pairs/km². The mean brood-production rate in individual years ranged from 29% to 49% (overall mean 36.8%), the chick-survival rate from 31% to 56% (43.1%), the young production from 1.6 to 2.8 young per adult (2.32 young/adult) and the annual survival rate of adult birds from 25% to 33% (28.3%). The population decrease in the 1990s was connected with the drop of reproductive success, including both the brood-production rate and the chick-survival rate, as well as with the decline of annual survival rate of adult birds. The decrease of brood-production rate and adult-survival rate probably resulted mainly from increased abundance of nest and incubating female predators (particularly foxes). Fluctuations in chick-survival rate were related to weather conditions, but also slight long-term decline was recorded, probably due to more intensive pesticide use.     

Do nomadic avian predators synchronize population fluctuations of small mammals? a field experiment

Three-to-five-year population oscillations of northern small rodents are usually synchronous over hundreds of square kilometers. This regional synchrony could be due to similarity in climatic factors, or due to nomadic predators reducing the patches of high prey density close to the average density of a larger area. We estimated avian predator and small rodent densities in 4–5 predator reduction and 4–5 control areas (c. 3 km² each) during 1989–1992 in western Finland. We studied whether nomadic avian predators concentrate at high prey density areas, and whether this decreases spatial variation in prey density. The yearly mean number of avian predator breeding territories was 0.2–1.0 in reduction areas and 3.0–8.2 in control areas. Hunting birds of prey concentrated in high prey density areas after their breeding season (August), but not necessarily during the breeding season (April to June), when they were constrained to hunt in vicinity of the nest. The experimental reduction of breeding avian predators increased variation in prey density among areas but not within areas. The difference in variation between raptor reduction and control areas was largest in the late breeding season of birds of prey, and decreased rapidly after the breeding season. These results appeared to support the hypothesis that the geographic synchrony of population cycles in small mammals may be driven by nomadic predators concentrating in high prey density areas. Predation and climatic factors apparently are complementary, rather than exclusive, factors in contributing to the synchrony.     

Population trend over 100?years and conservation needs of breeding sandwich terns ( Sterna sandvicensis ) on the German North Sea coast

The breeding population of the sandwich tern (Sterna sandvicensis) on the German North Sea coast has undergone substantial fluctuations throughout the last 100 years. Numbers of breeding birds were fluctuating quite strongly in the first 30 years of the twentieth century. From 1930 to the mid-1950s, a relatively steady decrease occurred. A minimum was reached in 1965 with 2,243 pairs. Around 1970, numbers increased quite markedly up to the mid-1990s and reached a centurial maximum with 10,138 pairs in 1996. Most recently, the numbers have dropped to only 5,681 pairs in 2005, the lowest number over the last 30 years. Some colonies have existed over long periods, others only for short periods, with often substantial and sudden changes. The distribution at sea was studied by transect counts from ships. During the reproductive period, high totals were found between the mainland coast and the islands, up to 30 km from the outer coast/island line. The seaward extent of the sandwich tern distribution coincided quite well with the 20-m depth line. Maximum foraging ranges for single colonies were estimated to be ca. 45 km for Trischen, ca. 35 km for Norderoog and ca. 30 km for both Scharh?rn/Nigeh?rn and Juist. Overall flight ranges for all colonies were estimated at 33.8 km for 95% of the birds. Germany has a high international responsibility for the protection of this species. Only a few colonies exist every year, making this species very vulnerable to anthropogenic disturbance, pollution events and fishing activities.

Differential Range Use between Age Classes of Southern African Bearded Vultures Gypaetus barbatus

Bearded Vulture Gypaetus barbatus movements were investigated in southern Africa to determine whether an individual''s age, sex or breeding status influenced its ranging behaviour and to provide the information required to guide conservation activities. Data from satellite transmitters fitted to 18 individuals of four age classes were used to determine range size and use. Because of the nature of the movements of marked individuals, these data could be used to determine the overall foraging range of the entire population, which was estimated to be 51 767 km². Although juvenile, immature and sub-adult birds used different parts of the overall range, their combined foraging range was 65% (33 636 km²) of the overall range. Average adult home ranges (286 km²) were only around 1% the size of the average foraging ranges of non-adults (10 540 –25 985 km²), with those of breeding adults being even smaller (95 km²). Home ranges of breeding adults did not vary in size between seasons but adults utilized their home range more intensively whilst breeding, moving greater distances during the incubation and chick hatching period. Range size and use increased as non-adults aged. Immatures and sub-adults had larger range sizes during winter, but range use of non-adults did not vary seasonally. Range size and use did not differ between the sexes in any of the age classes. Information on home range size and use enables specific areas within the species'' range to be targeted for management planning, education and conservation action.     

Tracking Natal Dispersal in a Coastal Population of a Migratory Songbird Using Feather Stable Isotope (δ2H, δ34S) Tracers

Adult birds tend to show high fidelity to their breeding territory or disperse over relatively short distances. Gene flow among avian populations is thus expected to occur primarily through natal dispersal. Although natal dispersal is a critical demographic process reflecting the area over which population dynamics take place, low recapture rates of birds breeding for the first time have limited our ability to reliably estimate dispersal rates and distances. Stable isotope approaches can elucidate origins of unmarked birds and so we generated year- and age-specific δ²H and δ³⁴S feather isoscapes (ca. 180 000 km²) of coastal-breeding Ovenbirds (Seiurus aurocapilla) and used bivariate probability density functions to assign the likely natal areas of 35 males recruited as first-year breeders into a population located in northwestern New Brunswick, Canada. Most individuals (80–94% depending on the magnitude of an age correction factor used; i.e. 28–33 out of 35) were classified as residents (i.e. fledged within our study area) and estimated minimum dispersal distances of immigrants were between 40 and 240 km. Even when considering maximum dispersal distances, the likely origin of most first-year breeders was<200 km from our study area. Our method identified recruitment into our population from large geographic areas with relatively few samples whereas previous mark-recapture based methods have required orders of magnitude more individuals to describe dispersal at such geographic scales. Natal dispersal movements revealed here suggest the spatial scale over which many population processes are taking place and we suggest that conservation plans aiming to maintain populations of Ovenbirds and ecologically-similar species should consider management units within 100 or at most 200 km of target breeding populations.     

A simple alternative to line transects of nests for estimating orangutan densities

We conducted a validation of the line transect technique to estimate densities of orangutan (Pongo pygmaeus) nests in a Bornean swamp forest, and compared these results with density estimates based on nest counts in plots and on female home ranges. First, we examined the accuracy of the line transect method. We found that the densities based on a pass in both directions of two experienced pairs of observers was 27% below a combined sample based on transect walks by eight pairs of observers, suggesting that regular line-transect densities may seriously underestimate true densities. Second, we compared these results with those obtained by nest counts in 0.2-ha plots. This method produced an estimated 15.24 nests/ha, as compared to 10.0 and 10.9, respectively, by two experienced pairs of observers who walked a line transect in both directions. Third, we estimated orangutan densities based on female home range size and overlap and the proportion of females in the population, which produced a density of 4.25–4.5 individuals/km² . Converting nest densities into orangutan densities, using locally estimated parameters for nest production rate and proportion of nest builders in the population, we found that density estimates based on the line transect results of the most experienced pairs on a double pass were 2.82 and 3.08 orangutans/km², based on the combined line transect data are 4.04, and based on plot counts are 4.30. In this swamp forest, plot counts therefore give more accurate estimates than do line transects. We recommend that this new method be evaluated in other forest types as well.     

The effects of traditional gathering on populations of the marine gastropod Strombus luhuanus linne 1758, in southern Papua New Guinea

Summary Little is known of the response of mollusc populations to predation by humans, particularly for tropical species. In this paper, we examine the effects of human predation on populations of the gastropod Strombus luhuanus in Bootless Inlet, Papua New Guinea, by documenting both the population biology of the shellfish and the shell-gathering practices of traditional and contemporary human groups. Strombus luhuanus occurs in local colonies and individuals of each sex from different colonies differed significantly in size. Sexual maturity is reached within two years after settlement, at which time the shell length stabilises at about 35–60 mm, and the shell lip thickens. There was also significant between-colony variation in density (8.35–23.39 individuals/m²), and colonies differed in the depth range of their distributions and the frequency of human collection visits. Traditional gatherers rarely collected individuals which were buried or subtidal. Contemporary collectors used different collecting methods, and gathered subtidal populations to a depth of 2.5 m. Both traditional and contemporary collectors gathered only individuals greater than 30 mm shell length, and in the contemporary sample the probability of being gathered increased significantly with shell length. This was due to size-dependent burying, which was greatest among young juveniles and least among adults. The traditional sample contained fewer shells in the largest size category (>45 mm) and more in the smallest (<40 mm), but this difference largely represents the pooling of shells from different collecting locations rather than widespread juvenisation of colonies due to exploitation. Stromb population densities at collected sites in PNG far exceeded those in comparable uncollected sites in northeastern Australia. We conclude that S. luhuanus displays high resilience to all gathering practices used to date, as a consequence of both its size-dependent burying and partly subtidal distribution, which provide refugia from human predation.     

A natural history of kra macaques (Macaca fascicularis Raffles, 1821) at the Kutai Reserve,Kalimantan Timur,Indonesia

Preliminary findings of a two-month pilot study of kra macaques (Macaca fascicularis Raffles, 1821) at the Kutai Reserve in Kalimantan Timur, Indonesia, are reported. Kra macaques spend most of their time in the forest canopy, though they may be seen in the morning and afternoon on the riverbanks. The sexually dimorphic kra exist in multi-male groups averaging about 18 individuals. There is about one group per km² of primary rainforest. Along the Sengata River, there were 2–5 groups per km², or 36–90 macaques per km² of riverine secondary forest. A home range for the primary study group was estimated to be about 0.8 km². The daily range of this group varied from 0.4 to 1 km.Kra macaque groups partition into subgroups when sleeping and foraging. Agonism between foraging subgroups was common. Predation, except from humans, appears minimal. Frequent associations and interactions between kra macaques, birds, and other mammals is described. It may be that birds or the kra are using the other to locate clumped scarce food resources. Grooming, copulation, play, interactions with the observer, and male protective displays are briefly described. Observation conditions were difficult and hence only a small number of social interactions were observed.     

Population ecology of the southern cassowary Casuarius casuarius johnsonii , Mission Beach north Queensland

Little is known of the ecology and population dynamics of the world’s largest avian frugivore. This study investigated the population of endangered southern cassowary at Mission Beach, northeast Australia, and examined the problems associated with determining population size and density of this keystone species. Using the results of an intensive field survey aimed at estimating absolute numbers of individual cassowaries, the appropriate sampling methodology for rare and elusive species was explored. Approximately 102 km² of rainforest was surveyed using 346 km of search transects. Of a total of 110 cassowaries, there were 49 adults (28 male, 19 female, 2 unknown), 28 subadults, 31 chicks, and 2 independent birds of unknown status. This is approximately 35% of the adult population previously estimated for the Mission Beach area. Overall adult cassowary density was 0.48 adults/km²; the density of independent birds, i.e. adults and subadults, was 0.78 birds/km². Mean indicative home range (IHR) for adult females and males was 2.13 and 2.06 km², respectively. Mean IHR of subadults was smaller at 0.95 km². It was concluded that the previous practice of surveying small areas at Mission Beach (<4 km²) has led to consistent overestimation of cassowary population density, up to six times its real number. It is shown that a sample plot between 5 and 15 km² is necessary to approximate true cassowary density. These findings have significant application to the conservation of cassowaries in New Guinea and in the Wet Tropics World Heritage Area of Australia.     

Anmerkungen zur Bestandsentwicklung des Uhus (Bubo bubo) in Bayern

Zusammenfassung In zwei Kerngebieten des Uhuvorkommens der Bundesrepublik Deutschland hat der Uhu in neuester Zeit scheinbar sehr stark zugenommen. In der Frankenalb (10 000 km²) schätzte man von 1955 bis 1964 etwa 30–40, Anfang der 70er Jahre etwa 50 und 1975–1980 75–83 Paare. In einem Ausschnitt der mittleren bayerischen Alpen (ca. 840 km²) waren um 1937 nur 3 Brutpaare bekannt, um 1975 mindestens 4; 1983/84 konnten jedoch mindestens 14 Brutpaare ermittelt werden. Die Zunahme ist zumindest größtenteils auf intensivere und systematische Kontrollen zurückzuführen. Der für die 30er Jahre vermutete Tiefstand des Bestandes in der Bundesrepublik dürfte weit höher gelegen haben als bisher vermutet, da zeitgenössische Quellen wahrscheinlich nur Teile des Bestandes erfaßten. Sicher lag der Bestand im 20. Jahrhundert wohl nie unter 50 Brutpaaren (bisherige Annahme 35), selbst zur Zeit des Minimums in der Bundesrepublik wahrscheinlich deutlich höher. Eine Obergrenze des bayerischen Brutbestandes von 200 Brutpaaren um 1980 ist durchaus realistisch. In den Alpen ist auch heute noch der Brutbestand völlig unzureichend bekannt. Das Aussetzen von Uhus hat in Bayern sicher keine Bedeutung für die Bestandsentwicklung gehabt. Der Median liegt für Todfunde ausgesetzter Uhus bei 0,43, für als Nestling beringte Wilduhus bei 1,9 Jahren. An Leitungen starben hochsignifikant mehr Wildvögel, an Straßen und Eisenbahnen dagegen hochsignifikant mehr ausgesetzte Vögel. Unterschiedliche Wanderneigung zwischen Wilduhus und ausgesetzten Vögeln ließ sich nicht sichern. Aussetzung und Wiedereinbürgerung sollten in Süddeutschland unbedingt unterbleiben und dürften auch im mittleren und nördlichen Deutschland mittlerweile überflüssig geworden sein. Eine Bestandsüberwachung und Kontrolle in ausgewählten Gebieten ist dagegen vordringlich.

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Some remarks on long term trends in the breeding population of the Eagle Owl (Bubo bubo) in Bavaria

Summary In two centres of its distribution in the Federal Republic of Germany the Eagle Owl has increased remarkably in recent years. Between 1955 and 1965 the population of the Frankonian Jura (ca. 10 000 km²) was estimated between 30 and 40 pairs, at the beginning of the seventies about 50, and in 1975/80 about 75–83 pairs. In an area of the Bavarian Alps (ca. 840 km²) only 3 pairs were known in 1937, at least 4 in 1975. In 1983/84, however, a thorough examination revealed at least 14 pairs in this area. The increase in both areas is most likely due to intensive and systematic checks in recent years. The lowest population level in the FRG, supposed for the thirties, was probably higher than estimated so far as contemporary sources apparently did not cover the whole population. During the 20^th century the population total of the FRG most likely has never been below 50 pairs and was probably higher even in times with minimum level. For 1980 an upper limit of 200 pairs in Bavaria seems to be realistic. In the Alps, however, the population size remains unsufficiently known even today. Release of captive bred birds didn't seem to have any increasing and stabilizing effect on the Bavarian population. The median for released birds found dead was 0,43, for wild chicks 1,9 years. Significantly more released birds died by traffic, whereas significantly more wild birds were victims of overhead lines. Differences in dispersal between wild and released birds seem likely, but could not be proved statistically. Releasing resp. reintroduction should be stopped in southern Germany; even in middle and northern Germany this conservation strategy seems to be unnecessary today. Survey and protection of breeding sites, however, should be continued or reorganized.

     

Water flux and energy use in wild house mice (Mus domesticus) and the impact of seasonal aridity on breeding and population levels

Summary Water turnover rate (WTR), urine concentration and field metabolic rate (FMR) were examined in house mice, Mus domesticus, permanently inhabiting roadside verge areas and seasonally invading crops in semi-arid wheatlands in South Australia. FMR was approximately proportional to body mass^0.5 and mean values varied from 4.8 ml CO₂ g^–1h^–1 (2.9 kJ g^–1d^–1) in autumn and winter, to 7.0 ml CO₂ g^–1h^–1 (4.2 kJ g^–1d^–1) in maturing crops during spring. WTR was independent of body mass, indicating that larger mice were selecting a diet containing moister foods. WTR was low in summer and high in winter, and in mice from crops varied from 165 ml l^–1 body water d^–1 (122 ml kg^–1d^–1) to 1000 ml l^–1d^–1 (725 ml kg^–1d^–1). Seasonal changes in WTR were less extreme on the roadside, where a greater diversity of food was available. In the crops, breeding occurred throughout summer during two of three years, but the population increased only in the one summer when mice had marginally higher WTR. On the roadside breeding and population growth were continuous during summer, except in a drought year. Avcrage urine concentration was inversely related to WTR, and varied from 2.0 to 4.8 Osm l^–1. The data indicate that the water conserving abilities of mice equal those of many desert rodents. The water conserving abilities of mice living in crops during summer were fully extended, and in some years aridity limited breeding success and population levels. The degree of moisture stress to which mice are exposed during summer appears to depend not only on rainfall but also on other factors such as availability of food and shelter, and the level of weed infestation in crops.     

Vogelbest?nde kultivierten Feuchtlandes Schleswig-Holsteins im Jahreslauf

Zusammenfassung Die Arbeit behandelt Vogelbestände im Niederungen-Grünland Schleswig-Holsteins. Die Jahresvogel-Bestände wurden auf 2 Untersuchungsflächen mit insgesamt 6,8 km² ermittelt (1976–1984). Zur Hochrechnung ausgewählter Gesamtbestände sind weitere Gebiete (Vergleichsflächen) einbezogen, summarisch bis zu 219 km² (bis 1993). Die Gesamtartenzahl beträgt 92 (Jahresmittel 37,4). Das jährliche Artenspektrum besteht zu 28% aus Brutvögeln und 72% aus Nicht-Brutvögeln (je 36% Brutvögel der Umgebung und Durchzügler/Gäste). Die mittlere Individuendichte beträgt 48,1/10 ha. Einmal im Jahr findet ein nahezu vollständiger Austausch von Nicht-Brutvögeln und (heimischen) Brutvögeln statt. Für dominierende und charakteristische Arten werden landesweit Bestände geschätzt. Im Winter bildet Grünland gegenüber anderen Agrarflächen ein sehr attraktives Habitat.

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Seasonal changes in bird communities of cultivated wetlands in Schleswig-Holstein/Germany

Summary The number of bird species and individuals were determined in 2 study plots (total 6,8 km² and 105 counts) in cultivated lowlands (grassland) of Schleswig-Holstein during 1976–1984. In order to estimate the total population of selected species additional comparison sites were surveyed. In total up to 219 km² (up to 1993) were surveyed. The average number of species observed each year was 37,4. On average 28% of the birds recorded each year were breeding species and 72% were non-breeders (of these 36% were breeding birds of the surrounding villages and woods and 36% were migrants and visitors). The average abundance was 48,1 individuals/10 ha. An almost complete exchange of non-breeders and local breeding birds occurs once a year. Estimated population sizes of dominant and characteristic species in Schleswig-Holstein are presented. Some lowland sites are very attractive habitats of international importance especially during the winter.

     

Point of no return – absence of returning birds in the otherwise philopatric willow warbler Phylloscopus trochilus

The return of individual birds to a specific area in successional years, i.e. philopatry, is a remarkable behavioural trait. Here we report on the remarkably reversed: the complete absence of returning individuals of a migratory passerine with otherwise pronounced philopatry. At a high latitude study site in Abisko (68°32?N, 18°80?E) in northern Sweden none of the banded adult willow warblers Phylloscopus trochilus returned to breed 2011–2014. This is in stark contrast to all other reports in the literature and also to our two southern study sites (at 56°56?N, 18°10?E and at 58°94?N, 17°14?E) where 18–38% of adults returned. We investigated this aberrant pattern found in Abisko by analysing three parameters known to influence philopatry; nest predation, breeding success and breeding density, and predicted that absence of philopatry should co‐occur with low breeding success, low breeding density and/or high nest predation. The results did not corroborate this, except that breeding density was lower at Abisko (49–71 pairs km^–2) than at the southern sites (106 pairs km^–2, 101 pairs km^–2). Instead, we suggest the hypothesis that the absence of philopatry is caused by an influx of southern, dispersal‐prone individuals deploying another breeding strategy and that this intra‐specific range expansion is enabled by milder climate and low population density.     

The current state of the Demoiselle crane population in the Transural steppe

The Demoiselle crane population was studied in the southern Chelyabinsk region (52°12′N; 60°21′E) during 1988–2008. Counts of nesting pairs were annually conducted over an area of 100–130 km² in May. The number of breeding pairs varied from 6.5 to 9.5 per 100 km²; on average, there were 8 pairs per 100 km² during 1989–1991. In 2000–2008, the population density increased from 7.5 to 12 pairs per 100 km², on average, 9.3 pairs per 100 km2. Demoiselle crane nesting in steppe pastures and perennial grass fields has been rarely observed for the last decade. Now the main nesting biotopes of the species are stubble fields accounting for up to 70% of all nidification cases documented. The decline in agricultural production in recent decades has resulted in the appearance of long-fallow lands, in which 17 to 35% crane pairs nest.     

Evidence of a large carnivore population recovery: Counting bears in Greece

Reliable population and density estimates are the cornerstone of effective conservation and management planning, as conservation priorities often arise in relation to population numbers. Despite increased public interest and costly conservation programs limited information on brown bear (Ursus arctos, Linnaeus, 1758) abundance and density in Greece exists. We carried out systematic non-invasive genetic sampling using hair traps on power poles, as part of a capture-mark-recapture study design in order to rigorously estimate abundance and density of the Pindos bear population in Greece. From 2007–2010 we identified 211 and estimated a mean of 182.3 individuals in four sampling areas; bear densities ranged from 10.0 to 54 bears/1000 km². These results indicate an important population recovery of this large carnivore in Greece in recent years; a conservative population estimate would place the population size in the entire country >450 individuals. Considering the results of the study and the increased negative interactions between humans and bears recorded currently in Greece, we suggest that systematic genetic monitoring using power poles should continue in order to collect the necessary information that will enable the definition of an effective Action Plan for the long-term conservation of this species.     

Can road mortality limit populations of pool-breeding amphibians?

We integrated road maps, traffic volume data, and pool locations in a modeling study to estimate the potential effects of road mortality on populations of pool-breeding spotted salamanders (Ambystoma maculatum Shaw). Population projections based on spotted salamander life tables imply that an annual risk of road mortality for adults of >10% can lead to local population extirpation; mitigation efforts (tunnels, road closures, and other measures) should seek to reduce road mortality rates to below this threshold. For central and western Massachusetts, we estimated that salamanders would be exposed to at least this threshold level of risk at 22–73% of populations (assuming a 100 vs. 500 m migration distance, respectively). We conclude that road mortality can be a significant source of additive mortality for individual spotted salamanders in many parts of the species’ range. Efforts to prevent such mortality by transportation planners are likely warranted strictly on a biological basis in areas with road densities >2.5 km per km² of landscape and traffic volumes >250 vehicles/lane/day within the migration range of a breeding population of spotted salamanders.     

Kleinfl?chen und Me?stellen zur Kalkulation gro?fl?chiger Brutvogelbest?nde:Buteo buteo undAccipiter gentilis in Schleswig-Holstein

Zusammenfassung Großflächige Bestandszahlen vieler Vogelarten sind nur über Teilerfassungen zu erhalten. Quantitative Gitterfeldkartierung mit Konfidenzintervallberechnung ermöglicht, Bestandsgrößen ohne Schätzanteile zu ermitteln und die Größen der Stichproben zu disponieren (Abb. 2). Die Kalkulation des Mäusebussard-Bestandes für Schleswig-Holstein mit 15 % an Probefläche beträgt 2891 Paare (Intervall 88–112 %), mit 6 % Probefläche nur geringfügig abweichend 3048 (oder gerundet 2400–3700) Paare innerhalb des 95%-Konfidenzintervalls (Abb. 2). Auf einer kleineren Bezugsfläche (1195 bzw. 750 km²) erbrachten Kalkulation mit 34 % Probefläche und Totalkontrolle nah beieinanderliegende Ergebnisse. Dabei lag das 95%-Konfidenzintervall im Rahmen der langfristigen Schwankungsbreite des Mäusebussards. An Meßstellen mit 37 % des Mäusebussard-Bestandes auf 360 km² ließ sich die Dynamik ermitteln (Abb. 3). Die Kalkulation des Habicht-Bestandes für Schleswig-Holstein mit 19 % Probefläche beträgt 366 Paare (Intervall 82–118 %=300–432 Paare, Abb. 2). Die Bestandsabnahme des Habichts (Abb. 3) nach 1980 scheint mit den Tötungen dieser Art zusammenzuhängen.

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Calculating breeding bird populations by sampling small areas:Buteo buteo andAccipiter gentilis in Schleswig-Holstein, FRG

Summary Population size estimates of various bird species in large areas can only be obtained by sampling small and representative plots. Quantitative grid mapping (1=3.75 km, A=14.06 km²) and the calculation of confidence intervals allow the size of the population to be determined. The size of the sample plots can be determined using the curve of the confidence limits (fig. 2). In Schleswig-Holstein, the breeding population of the Buzzard (13 600 km² excluding coastal meadows), is calculated at 2.891 pairs (confidence limits 88–112 %), based on sample plots (15 % of the total area, fig. 1). Based on only 6 % of the representative sample plots similar results can be found: 3,048 pairs. That is within the 95 % confidence limits of the estimation on the basis of 15 % (fig. 2). An investigation of 34 % of a smaller area (750 km²) revealed almost the same results as an investigation of the total area. The 95 % confidence limits lie within the long-term population dynamics of the Buzzard. The population dynamics can be determined by constant assessment sites (distributed over an area of 360 km²) containing 37 % of the Buzzard population (fig. 3). For the Goshawk population the same calculation, based on 19 % of the sample plots, shows 366 pairs for Schleswig-Holstein (95 % confidence limits 82–118 %=300–432 pairs). The decrease in the population of the Goshawk after 1980 seems to be associated with persecution.

     

High annual variability in reproductive success and survival of an Antarctic seabird,the snow petrel Pagodroma nivea

Demographic parameters were estimated for snow petrels Pagodroma nivea nesting at Pointe Géologie Archipelago, Adélie Land, Antarctica between 1963 and 1990; 21 years of data on adult survival and 27 years of data on breeding success are available. The average age of first return and first breeding were 8.1 and 9.9 years respectively and there was no signifcant difference between the sexes. The overall breeding success averaged 51.3% and was very variable between years (21–80%). Breeding failure was mostly due to incubation failure and annual breeding success was negatively correlated with average snow falls in October–November and October–March. Breeding frequency was very low, averaging 52% of seasons during a reproductive lifetime. Good quality sites, with high occupancy rate and high breeding success were few in the study plots. Poor years in 1966–1967, 1976–1977 and 1983–1984, with low breeding success, very low proportions of nets with breeding attempts and high numbers of non-breeders, occurred 1 year after large-scale El Niño Southern Oscillation (ENSO) events. Snow petrels exhibited very low philopatry. Only 45 birds have been recovered in the study plots from a total of 1115 banded fledglings giving an estimated rate of return of 12.9% between fledging and 3 years old. Annual survival between 3 and 10 years was 91.4%. Annual adult survival (93.4%), though variable, was low during poor years of 1977–1978 and 1983–1984. Adult survival of males (94.7%) was not significantly different from that of females (93.9%). Over the study period, the population of Pointe Géologie was stable. Using the estimated parameters, a Leslie model gave a growth rate of 0.948%, which was probably compensated by immigration (5.7% per year). Restricted numbers of good-quality sites at the place of birth could have led young birds to prospect other colonies and could have selected low philopatry. High adult survival, strong site tenacity and capacity to spread breeding over a long lifetime are probably part of the adaptive strategy of this small fulmarine petrel facing highly variable environmental conditions.     

Use of cloacal sexing techniques in mark-recapture estimates of breeding population size in Wilson's stormpetrel Oceanites oceanicus at South Georgia

Summary Many stormpetrel species breed in habitats where their populations cannot be estimated by direct counts of burrows or birds; mark-recapture experiments have been confounded by the presence of many wandering non-breeders. With a population of Wilson's Stormpetrel Oceanites oceanicus at Bird Island, South Georgia, we tried to estimate the proportion of breeding females in samples obtained during a mark-recapture experiment. These were identified by measurements of the cloaca, which greatly enlarges at egg-laying. A concurrent experiment with individually marked birds determined that breeding females could be discriminated from males and non-breeders for c 30 days after laying. The technique is probably applicable to other petrels, though it will work best with those that lay most synchronously. The overall population estimate was 4841–5515 birds (SE 856–1417); estimates of breeding females gave a population of 2300 paris early in the incubation period and 1400 pairs near hatching.