Differential Begging and Locomotory Behaviour by Early and Late Hatched Nestlings Affecting the Distribution of Food in Asynchronously Hatched Broods of Altricial Birds

Distribution of food to early and late hatched nestlings was studied in asynchronously hatched broods of the great tit Parus major, the blackbird Turdus merula, and the fieldfare T. pilaris. Food distribution is related to the locomotory and begging behaviour and positions in the nest of these nestlings. Late hatched (small) nestlings were found to beg more often per feed than bigger nestlings and move more towards favoured positions in the nest to counteract selective feeding of bigger young. The functional significance of these differences in the behaviour of early and late hatched nestlings are discussed. It is argued that they are adaptive by 1) ensuring that each nestling survives when food supplies are ample, and 2) by mediating an optimal brood reduction when food is insufficient to raise the entire brood. The roles of asynchronous hatching, and selective feeding which follows from differential behaviour of early and late hatched young are discussed in relation to food conditions during the breeding season.     

4. UNUSUAL EXPERIENCES WITH BIRDS

Earlé, R. A. 1989. Breeding biology of the Redbreasted Swallow Hirundo semirufa. Ostrich 60: 13–21.

The two races of the Redbreasted Swallow Hirundo semirufa seem to have separate breeding seasons with the northern race H. s. gordoni breeding April-July, while most records for the nominate race fall in October-February. All nests studied were in concrete culverts less than 1 m high. Eggs laid in second clutches by individual females weighed significantly less than eggs laid in first clutches. Eggs hatched on average 16,2 days after incubation started or 18–21 days after the eggs were laid. Only females incubated. Chicks fledged 23–25 days after hatching and reached a maximum body mass of about 31,5 g on day 18 before a steady decline in mass until fledging. Most nesting failures resulted from infertile eggs or starvation of young in the nest (16,2% of all young starved). Overall breeding success was 60,6%. In all, 81,8% of first clutches produced fledglings but only 44,4% of second clutches. Over a three year period 4,9 young were produced per pair breeding in the area (1,6 young/pair/breeding season).     

Seasonal variations in numbers,biomass and breeding patterns of dung beettles [Coleoptera: Scarabaeidae] in Southern France

Seasonal variations in numbers and biomass and breeding of 28 species ofScarabaeidae-Scarabaeinae andGeotrupidae were studied at 2 temperate sites and 2 mediterranean sites in southern France in 1978 and 1979, using cattle-dung baited pitfall traps. Maximum dung burial occurred when females were parous and ovipositiong (i.e. during spring at the mediterranean sites and summer at the temperate sites). Using biomass as a measure of dung burial the most important spring active beetles at the mediterranean sites were:Budas bison, B. bubalus, Scarabaeus laticollis, Onthophagus lemur andCopris hispanus, and at the temperate sites:C. lunaris, O. vacca, andO. ovatus. These results confirmed the previous choice ofC. hispanus, C. lunaris, B. bison andO. vacca for introduction into Australia. In addition it is suggested thatB. bubalus, S. laticollis andO. lemur be considered for introduction into mediterranean areas of south western Australia to complement those species already introduced for bush fly control.      

BREEDING BEHAVIOUR OF OSPREYS PANDION HALIAETUS IN SCOTLAND

Ospreys Pandion haliaetus nested at a site near Loch Garten, Inverness-shire continuously from 1959 to 1973. Each year the Royal Society for the Protection of Birds has organized a continuous watch on the eyrie in the breeding season. The detailed records kept of the activities of Ospreys at the nest by those participating in the watch were analysed and the results presented here. Ospreys are migratory and arrived in the breeding area in early April. Nesting material was usually added to an existing eyrie platform. The male collected more material than the female. The female lined the nest cup. The extent of nest building activity and the frequencies of mating and other activities prior to laying varied markedly from year to year. These differences may have been related to changes in the identity of the nesting female, but the birds were not individually marked. Both sexes incubated but the female took the greater share and normally incubated at night. When the young hatched they were brooded by the female. The female stayed in the vicinity of the nest for most of the time until the young fledged at about 53 days old. The male Osprey caught almost all the fish eaten by his mate and young during the breeding season. The number of fish caught per day increased markedly after the young hatched. Pike Esox lucius and Trout Salmo trutta were the main species taken, and some Rainbow Trout Salmo gairdnerii were identified. There were seasonal and diurnal changes in the size and the species composition of the catch. The effects of weather conditions on hunting are examined. The occurrence of Ospreys other than the resident birds at the nest site is described. The behaviour of another pair of Ospreys which repeatedly failed to hatch eggs is described. There was an instance of egg eating in this pair, and some differences in behaviour were found between these birds and those at Loch Garten whose breeding success was good. The breeding biology of Ospreys is compared with that of other British diurnal birds of prey. In other species the female leaves the young unguarded at some stage in the nestling period and hunts food for them, whereas female Ospreys do not usually hunt in the nesting period.     

Smaller size of harlequin toads from populations long exposed to the fungal disease chytridiomycosis

Pathogens can exert great selective pressures on the life history traits of their hosts. Species experiencing high mortality throughout their adulthood can benefit from breeding earlier. Chytridiomycosis, a fungal disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), has been a major driver of extinction for harlequin toads (Atelopus) and continues to be frequent cause of adult mortality for species persisting with endemic infections. We compared the body size of Atelopus cruciger between a remnant population long exposed to Bd (post-epidemic) and populations sampled before the presumed Bd outbreak in the late 80s (pre-epidemic). Reproductive female and male toads from pre-epidemic populations were significantly bigger than those from post-epidemic populations at similar altitudes, suggesting that toads from post-epidemic populations are breeding earlier. A significant positive relationship between body size and the number of eggs in oviducts suggests a trade-off between the benefit of breeding earlier and the cost of smaller clutch sizes. This cost–benefit relationship is likely to change along elevation gradients because the number of eggs relative to body size tends to be lower at higher elevations. By breeding earlier harlequin toad populations long exposed to Bd can increase their demographic competence, particularly in lowland habitats, where the cost–benefit relationship of breeding earlier tends to be more favorable. Abstract in Spanish is available with online material.     

Orientation behaviour of toads (Bufo bufo) displaced from the breeding site

Summary The sensory basis and spatial range of orientation to the breeding site were studied in the toadBufo bufo, during two breeding seasons. Toads were displaced passively from their breeding pond and fitted with a tracking device to record the path of migration in individuals. The directional choice and the straightness of trails after release were used to quantify the effect of experimental treatments. In both years, control (untreated): toads headed to the breeding site with the same precision at all release sites. The initial orientation of toads blinded by opaque tape over their eyes. did not differ from controls, but the return paths were not as direct. The directional choice of anosmic toads was apparently random, however, individuals followed a straight path in a chosen direction. Anosmic toads also blinded were completely disoriented, moving in cycloid trails. Bar magnets glued to the head caused an increase in dispersion of toads. However, in some individual releases a directional bias without increased dispersion was observed. Sky conditions (clear or overcast) did not influence the initial orientation or the dispersion of toads. Nevertheless, the breeding site component was significantly correlated with wind direction in relation to the breeding site. Wind blowing from the breeding site improved the initial orientation, whereas wind from the opposite direction reduced the breeding site component. The spatial range for the ability to relocate the breeding pond after displacement exceeded 3 km, but the time taken to select the correct direction increased with the displacement distance. The results indicate that after displacement the initial orientation ofB. bufo is based mainly on olfactory and magnetic cues, with visual control of straightness.     

Non‐invasive treatments of luteinizing hormone‐releasing hormone for inducing spermiation in American (Bufo americanus) and Gulf Coast (Bufo valliceps) toads

As many as 20% of all assessed amphibian species are threatened with extinction, and captive breeding programs are becoming important components of conservation strategies for this taxon. For some species, exogenous hormone administration has been integrated into breeding protocols to improve propagation. However, most treatments are administered by an intraperitoneal injection that can be associated with some risks. The general goal of this study was to identify a non‐invasive method of applying luteinizing hormone‐releasing hormone (LHRH), which reliably induces sperm release in toads. Specific objectives were to 1) test the spermiation response after topical application of different LHRH doses to the abdominal seat region, 2) evaluate the effects of adding the absorption enhancers dimethyl sulfoxide (DMSO), acetone, and glyceryl monocaprylate (GMC) to the LHRH, 3) assess the spermiation response after oral delivery of LHRH in a mealworm vehicle, and 4) compare sperm characteristics and spermiation responses to treatments in two different toad species. Male American (n = 9) and Gulf Coast (n = 7) toads were rotated systematically through a series of treatments. Urine was collected and evaluated for the presence of sperm at 0, 3, 7, 12, and 24 hours post‐treatment. There were no statistical differences in spermiation induction or sperm characteristics between American and Gulf Coast toads after the treatments. Oral administration of 100 μg LHRH was occasionally successful in inducing spermiation, but results appeared largely unreliable. Ventral dermal application of 100 or 10 μg LHRH in 40% DMSO were more effective (P < 0.05) at inducing spermiation compared with the other treatments tested, eliciting sperm release in more than 70% of toads tested. In breeding programs for rare and/or fragile anurans, these non‐invasive methods of exogenous hormone administration might be preferred over intraperitoneal injections. Zoo Biol 20:63–74, 2001. © 2001 Wiley‐Liss, Inc.     

Seasonal changes in the migratory behaviour of the toad Bufo bufo: direction and magnitude of movements

Summary The migratory behaviour of the toad Bufo bufo was studied from February 1985 to April 1986 in the submontane region of Bavaria, West Germany. Toads were fitted with a mechanical tracking device to record individual paths of migration. Three aspects of migratory behaviour were quantified: orientation in relation to the breeding site, straightness of path, and locomotory activity. The annual activity period began with migration from the hibernation sites to the breeding pond in April. The paths went straight towards the breeding pond independent of the distance (70–420 m). During the period of oviposition the preference for the breeding site direction vanished and toads moved away from the breeding pond, but in less straight paths than before. In summer migratory activity decreased considerably and was restricted to small areas, the home ranges, at distances of 55–1600 m from the natal breeding pond. The straightness of path was rather low, because toads often returned to their starting points. During rainy nights toads occasionally left their home ranges for extensive excursions. In autumn most toads again migrated towards the breeding pond, but paths were significantly less straight and direct than in spring. However, toads stopped before reaching the breeding pond and hibernated in holes or under the leaf layer. The mortality rate of tracked toads was about 45%. The relative influence of 17 environmental variables on locomotory activity was evaluated by principal component analysis and stepwise multiple regression. Temperature at night and rainfall variables accounted for significant amounts of variance, whereas temperature by day, air humidity, and atmospheric pressure showed no correlation. Activity decreased if temperature approached 0° C or after long periods without rainfall. Within a certain range of tolerance, however, the locomotory activity of the toads was widely independent of environmental factors, indicating that endogeneous factors are more important sources of variation in the migratory behaviour of these toads than commonly assumed.     

Seasonal variation in positional behavior of malagasy lemurs

I describe the positional behavior of four species of Malagasy lemur (Propithecus diadema, Eulemur fulvus rufus, Eulemur rubriventer,and Varecia variegata)at two times of year at Ranomafana National Park,Madagascar. There were significant seasonal differences in locomotor behavior in all species except P. diademaAmong the lemurids, leaping was more frequent and quadrupedism less frequent in the dry season. Only E. rubriventerexhibited seasonal differences in posture, and there were few seasonal differences in support use. The observed differences in positional behavior were not the result of differences in activity budget or in microhabitat use attributable to seasonal variation in resource use.     

2nd World Congress of Herpetology

Abstract Natterjack toads (Bufo calamita) form metapopulations consisting of interacting local and temporal breeding assemblages. The gene flow between simultaneously reproductive local populations is limited at the adult stage to about 2% roaming males and around 20% of females. The gene flow between temporal populations breeding successively at the same locality is based on about 0–15% of males and 0–29% of females reproducing in different temporal breeding assemblages. The annual mortality rate of males ranges between 50 and 60%, corresponding to a maximum life expectancy of about 7 years. The main cause of local extinction is always deterioration of the habitat, namely destruction of the breeding habitat or a dry climate.     

Under adverse conditions,older small tree finch males (Camarhynchus parvulus) produce more offspring than younger males

Females of many bird species prefer mating with older males, presumably because they provide superior parental care and possibly superior genes. A previous study found that female small tree finches (Camarhynchus parvulus) preferred pairing with old males and had a higher breeding success when paired with old males because their nests were more concealed, higher up in the canopy and therefore less likely to be depredated. However, causes for brood loss have changed over the last decade: predation of small tree finch nests has decreased, whereas brood losses due to parasitism by the invasive parasitic fly Philornis downsi have increased. In the present study, we investigated (a) how the change in predation and parasitism by P. downsi influenced the breeding success of small tree finches, (b) whether there were still differences in breeding success between young and old males, (c) whether P. downsi infestation had a differential effect on nests of young and old males and (d) whether young and old males differed in foraging success. During 2012–2016, we found an overall low influence of predation and a high influence of P. downsi, but neither differed between nests of young and old males. Nests of old males had more fledglings than those of young males. However, the difference in breeding success disappeared when P. downsi numbers were experimentally reduced by injecting an insecticide into nests. This indicates that older males were able to compensate for the detrimental effects of parasitism.     

Unique multiple paternity in the endangered big‐headed turtle (Platysternon megacephalum) in an ex situ population in South China

Understanding the mating system and reproductive strategies of an endangered species is critical to the success of captive breeding. The big‐headed turtle (Platysternon megacephalum) is one of the most threatened turtle species in the world. Captive breeding and reintroduction are necessary to re‐establish wild populations of P. megacephalum in some of its historical ranges in China, where the original populations have been extirpated. However, the captive breeding of P. megacephalum is very difficult and this may be due to its mysterious reproductive strategies and special behavior (e.g., aggressive temperament and territoriality). In this study, we achieved successful captive breeding of P. megacephalum by creating a habitat that mimics natural conditions and then investigated its mating system using microsatellite makers. A total of 16 clutches containing 79 eggs of P. megacephalum were collected, and 52 were hatched successfully over two breeding seasons. Of the 15 effective clutches, 6 clutches (40%) exhibited multiple paternity. There was no significant correlation between clutch size and multiple paternity, and no significant difference in hatching success between multiple‐sired and single‐sired clutches. However, there was significant correlation between male body size and the number of offspring, with higher‐ranked males contributing to more clutches. Our results provide the first evidence of multiple paternity and male hierarchy in P. megacephalum. These findings suggest that multiple paternity and male hierarchy should be considered in captive breeding programs for P. megacephalum, and creating a habitat that mimics natural conditions is an effctive way to achieve successful captive breeding and investigate the mating systems of this species.     

CHANGES IN THE MELANOPHOROTROPIC FUNCTION OF THE PITUITARY GLAND ACCOMPANYING BLINDNESS IN XENOPUS LAEVIS DAUDIN

A number of cases of blindness appeared among a group of cultured Xenopus laevis. The blind toads lacked eyeballs and optic nerves and were consistently dark in color. Similar anatomical changes in the head and pigmentation were produced experimentally by removing the eyeballs of tadpoles or young adult toads. The dark pigmentation of blind Xenopus: was shown to be due to the continuous release of MSH from the pars intermedia of the pituitary, since hypophysectomy led to the complete blanching of the dermal and epidermal melanophores. MSH activity in the pars intermedia of blind toads was extremely high in comparison with that of normal animals. No special difference with respect to the general growth and behaviour was found between normal and blind Xenopus, which suggests that the pituitary functions other than that of the pars intermedia are not affected by the state of the optic nerves. These observations suggest that the retrogressive degeneration of the optic nerves exerts a profound effect on the secretory activity of the pars intermedia via the hypothalamic controlling center.     

4. A FIELD NATURALIST'S PEREGRINATIONS. BIRD NOTES FROM A NORTHERN SECTOR OF SOUTHERN RHODESIA—Part III

Boyer, H. J. 1988. Breeding biology of the Dune Lark. Ostrich 59:30-37.

The peak of the breeding season of the Dune Lark Mirafra erythrochlamys occurred in January and February and was not dependent on rainfall. Most nests were domed, although one undomed nest was recorded. Ninety-one percent of clutches were of two eggs (mean = 1,9; range 1–2; n = 11). The eggs are described and measurements given. Incubation, by the female only, began with the laying of the second egg, and hatching occurred after 13–14 days. Growth and development of nestlings are described. The young left the nest after 12–14 days, and post-nestling parental care lasted for approximately one month. Sixty-one percent of eggs hatched. and 28% produced young which successfully left the nest. Most losses of eggs and young were the result of predation.     

Survivorship and growth in the larvae of Luehdorfia japonica feeding on old leaves of Asarum megacalyx

Although the papilionid butterfly Luehdorfia japonica, usually lays eggs on new leaves of the host plant (Asarum sp.; Aristolochiaceae), eggs of the butterfly were frequently found on old leaves of Asarum megacalyx in Suyama, Tokamachi, Niigata prefecture. Larvae hatched on new leaves and those hatched on old leaves did not show significant differences in their survival rate in the field. In laboratory breeding, about 90% of larvae that were fed old leaves survived and developed normally to the pupal stage. Their growth rate, however, was slightly lower than those that were fed new leaves. No nutritional differences were found between the old and new leaves. The reason why oviposition on the old leaves was so frequent and why larvae that hatched on old leaves could survive in the study area is discussed.     

Genetic rescue of an inbred captive population of the critically endangered Puerto Rican crested toad (<Emphasis Type="Italic">Peltophryne lemur</Emphasis>) by mixing lineages

The Puerto Rican crested toad (Peltophryne lemur) is currently composed of a single wild population on the south coast of Puerto Rico and two captive populations founded by animals from the northern and southern coasts. The main factors contributing to its decline are habitat loss, inundation of breeding ponds during storms, and impacts of invasive species. Recovery efforts have been extensive, involving captive breeding and reintroductions, habitat restoration, construction of breeding ponds, and public education. To guide future conservation efforts, genetic variation and differentiation were assessed for the two captive colonies and the remaining wild population using the mitochondrial control region and six novel microsatellite loci. Only two moderately divergent mitochondrial haplotypes were found, with one fixed in each of the southern and northern lineages. Moderate genetic variation exists for microsatellite loci in all three groups. The captive southern population has not diverged substantially from the wild population at microsatellite loci (F _ST = 0.03), whereas there is little allelic overlap between the northern and southern lineages at five of six loci (F _ST > 0.3). Despite this differentiation, they are no more divergent than many populations of other amphibian species. As the northern breeding colony may not remain viable due to its small size and inbred nature, it is recommended that a third breeding colony be established in which northern and southern individuals are combined. This will preserve any northern adaptive traits that may exist, and provide animals for release in the event that the pure northern lineage becomes extirpated.     

Relationship of Endangered Amphibians to Landscape Disturbance

Abstract: We examined the density of 2 endangered amphibians, natterjack toads (Bufo calamita) and yellow-bellied toads (Bombina variegata), in 150 breeding pools at each of 2 military training areas in the German state of Bavaria. We selected pools to ensure a wide range of observable ground disturbance resulting from military vehicular traffic during cross-country maneuvers. Both species exhibited significant affinity for pools with high levels of ground disturbance. Natterjack toads preferred pools with 80–100% ground disturbance; yellow-bellied toads preferentially occupied pools with 40–100% ground disturbance. Pools occupied by the target species were characterized by higher levels of bare ground and minimal vegetation. Among other observed amphibians, European edible frogs (Rana esculenta) preferred pools with ≤60% ground disturbance, less bare ground, more vegetative cover, and disturbance >2 years old. Common tree frogs (Hyla arborea), smooth newts (Triturus vulgaris), and alpine newts (T. alpestris) showed no preference for level of disturbance; densities were correlated to parameters apparently unrelated to disturbance. The habitat mosaic created by the heterogeneous nature of military training disturbance may help explain the high biodiversity that often characterizes military training areas. Preservation of native biodiversity is dependent on maintaining an appropriate disturbance regime that, in turn, maintains a habitat mosaic conducive to the presence of native species adapted to a broad disturbance—succession continuum. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):738–744; 2008)     

Growth rates of young-of-year shovelnose sturgeon in the Upper Missouri River

Information on growth during the larval and young‐of‐year life stages in natural river environments is generally lacking for most sturgeon species. In this study, methods for estimating ages and quantifying growth were developed for field‐sampled larval and young‐of‐year shovelnose sturgeon Scaphirhynchus platorynchus in the upper Missouri River. First, growth was assessed by partitioning samples of young‐of‐year shovelnose sturgeon into cohorts, and regressing weekly increases in cohort mean length on sampling date. This method quantified relative growth because ages of the cohorts were unknown. Cohort increases in mean length among sampling dates were positively related (P < 0.05, r² > 0.59 for all cohorts) to sampling date, and yielded growth rate estimates of 0.80–2.95 mm day⁻¹ (2003) and 0.44–2.28 mm day⁻¹ (2004). Highest growth rates occurred in the largest (and earliest spawned) cohorts. Second, a method was developed to estimate cohort hatch dates, thus age on date of sampling could be determined. This method included quantification of post‐hatch length increases as a function of water temperature (growth capacity; mm per thermal unit, mm TU⁻¹), and summation of mean daily water temperatures to achieve the required number of thermal units that corresponded to post‐hatch lengths of shovelnose sturgeon on sampling dates. For six of seven cohorts of shovelnose sturgeon analyzed, linear growth models (r² ≥ 0.65, P < 0.0001) or Gompertz growth models (r² ≥ 0.83, P < 0.0001) quantified length‐at‐age from hatch through 55 days post‐hatch (98–100 mm). Comparisons of length‐at‐age derived from the growth models indicated that length‐at‐age was greater for the earlier‐hatched cohorts than later‐hatched cohorts. Estimated hatch dates for different cohorts were corroborated based on the dates that newly‐hatched larval shovelnose sturgeon were sampled in the drift. These results provide the first quantification of growth dynamics for field‐sampled age‐0 shovelnose sturgeon in a natural river environment, and provide an accurate method for estimating age of wild‐caught individuals. Methods of age determination used in this study have applications to sturgeons in other regions, but require additional testing and validation.     

Factors influencing offspring traits in the oviparous multi-clutched lizard,<Emphasis Type="Italic">Calotes versicolor</Emphasis> (Agamidae)

The determinants of offspring size and number in the tropical oviparous multi-clutched lizard,Calotes versicolor, were examined using both univariate and multivariate (path) analyses. InC. versicolor maternal snout-vent length (SVL) and body condition influence clutch mass and clutch size but have no significant influence on offspring size. The positive effect of maternal SVL and body condition on offspring number is counterbalanced by a negative effect of breeding time on egg mass. In fact, breeding time directly influences the offspring body mass and condition through variation in the egg mass. There is a trade-off between offspring mass and condition with offspring number, and breeding time influences both. Offspring hatched from the eggs of early (May–June) or mid (July–August) breeding periods invariably show lower mass and condition than those hatched from the eggs of late breeding season (September–October). Yet, there is no variation in offspring SVL among early, mid and late clutches. Thus, inC. versicolor offspring SVL is optimized while body mass and condition are not optimized.     

14j?hrige Beobachtungen zur Vermehrung des Waldkauzes (Strix aluco L.)

Zusammenfassung Von 1958 bis 1971 wurde die ca. 20 Paare zählende Waldkauzpopulation eines Westberliner Waldgebietes kontrolliert. In diesen 14 Jahren hatten von 232 Paaren 107 (46,1%) Junge; über 50% brüteten demnach erfolglos.Pro erfolgreiches Paar ergaben sich 2, pro Paar überhaupt nur 0,92 Junge. Der Bruterfolg war in den einzelnen Jahren sehr unterschiedlich (Tab. 1).Unter 13 359 in Gewöllen nachgewiesenen Wirbeltieren betrafen 34,9% Vögel, 29% die 3Apodemus-Arten, 16,7%Microtus, 12,7% Insektivoren, 7,6% Amphibien. Keine der vielen Beutetierarten hatte einen dominierenden Anteil in der Gesamtbeute. In der Winternahrung bildeten jedoch über 50% der Beute Kleinvögel, in Spitzenjahren sogar 67%.Die jährlichen Unterschiede in der Vermehrungsrate des Waldkauzes scheinen vor allem auf die wechselnde Bestandsdichte der Gelbhalsmaus(Apodemus flavicollis), des Hauptbeutetieres, zurückzuführen zu sein (Abb. 2). Eine Berliner Stadtpopulation (17 Paare), die sich zu 70% von Vögeln, vor allem Haussperlingen, ernährte, zog 3,2 Junge pro erfolgreiches Paar auf.Bei den Eulen scheint im Gegensatz zu den Greifvögeln eine Regulation der Vermehrung in Abhängigkeit vom Nahrungsangebot nicht nur durch Reduktion der Gelegegröße, sondern vor allem auch durch totalen Brutausfall zu erfolgen.

---

Fourteen Years observations on the reproduction of a Tawny Owl population

Summary From 1958–1971 the Tawny Owl(Strix aluco) population in the Grunewald Pine forest of Berlin (West) was observed. About 20 pairs breed yearly in this wood (31 km²). A total of 232 pairs was checked during these 14 years; 107 pairs (46,1%) had fledged 214 young (2 young per successfull pair). In many years most of the pairs did not rear any young, for instance in 1968 only 4 (=21%) out of 20 pairs had young. 13 359 vertebrates were found in the pellets of the owls: 34,9% birds; 29%Apodemus (most of themA. flavicollis), 16,7%Microtus (4 species), 12,7% shrews and other small mamals, 7,6% toads and frogs, 0,09% fishes. Of the numerous prey species none showed a preponderance while in wintertime the proportion of birds was more than 50%.The breeding rate seems to be due to the yearly changing density of the main prey: in years of a high density ofApodemus flavicollis the reproduction of the Tawny Owls was high, in years of low density a great number of the owls did not rear young (figure 2). Another factor of high or low reproduction is perhaps the quantity of food available during the time immediately before laying (fig. 3). The low breeding results of this woodland population are in contrast to the reproduction figures of another Berlin population living in parks and cemeteries inside of the city. 17 pairs were observed; they had 54 young (3,2 young per pair). Here the food situation is much better: 70% of the prey were birds, most of them House Sparrows(Passer domesticus) and Greenfinches(Carduelis chloris).