Breeding biology of the Barn Owl Tyto alba in central Mali

Data were obtained on 178 clutches of African Barn Owls in central Mali from four breeding seasons during 1979–1983. Significantly more clutches were laid in 1979–1980 and significantly fewer in 1980– 1981 than the average for the 4 years and there were significantly more clutches laid in the middle period of the annual breeding season. The egg volume was significantly smaller at the beginning of the breeding season and significantly larger in the middle than the overall mean with eggs of second clutches being larger than those of first clutches. The clutch size was 605 eggs of which 479 hatched. The number of young fledged per successful nest was 319 and was 1 83 for all nesting attempts. The month was the only variable shown to affect significantly the clutch size, eggs hatched and fledging rate, the highest success rates being associated with the middle of the breeding period. The average interval between the hatching of eggs was 2–31 days. Survival rates (47'1%) to fledging were significantly affected by year (1981–1982 being the least) and month (mid-season birds the best). The order of hatching significantly affected age at death or disappearance, the first-hatched birds surviving the longest. The year significantly affected age at fledging, the young from the year in which most clutches were laid leaving the nest at the youngest age and those associated with the year having the least number of clutches remaining in the nest the longest. The month of hatching also affected fledging age, birds at the extremes of the breeding season fledging at older ages. The discussion compares these data with those from elsewhere.     

Effects of the risk of competition and predation on large secondary cavity breeders

The effects of competition and risk of predation on secondary cavity breeders were examined between the 2008 and 2009 breeding seasons using an experimental design manipulating two nest entrance sizes (large entrances allowed Barn Owls (Tyto alba) to enter, while the small entrances excluded them). During the 2009 breeding season, the entrance sizes of nest boxes were exchanged, so that if during one year a nest box in a particular location had a small entrance, the second year it had a large entrance and vice versa. Barn Owls and Eurasian Kestrels (Falco tinnunculus) occupied 67.3 and 17.3%, respectively, of large entrance nest boxes. Significantly more Jackdaws (Corvus monedula), House Sparrows (Passer domesticus) and Scops Owls (Otus scops) bred in nest boxes with small than with large entrances. After nest box entrance sizes were exchanged, Barn Owls and smaller species did not breed in the same nest boxes with the new entrance size. Jackdaws probably did not breed in large entrance nest boxes due both to exploitation competition (Barn Owls and Eurasian Kestrels occupied the majority of large entrance nest boxes), and may also have avoided empty nest boxes because of the risk of interference competition; whereas smaller species may have also avoided large entrance nest boxes due to risk of predation.     

The feeding and breeding ecology of Barn Owls Tyto alba in Peninsular Malaysia

Barn Owls have only recently colonized Peninsular Malaysia, nesting in the roof spaces of houses in oil palm estates and feeding on the rats which inhabit these plantations. Pellet analysis showed that the prey spectrum was confined almost entirely to three species of the genus Rattus which are the major pests of oil palm. There was no annual variation in diet. Breeding showed a broad seasonality but occurred in all months of the year. Mean clutch and brood sizes of 6.6 and 4.6 respectively were recorded, most pairs producing two broods a year although on two occasions three were raised. Overall hatching success was 69.0% with first clutches more successful (79.9%) than second (57.3%). First broods fledged 86.1% and second broods 69.1% of young fledged. Comparison of growth rates of different sized broods suggested that there is a physiological maximum at which all broods proceed irrespective of brood size. The behaviour al changes needed in hunting techniques when colonizing dense plantations rather than the more usual open habitat of Barn Owls is discussed. The breeding strategy seems to be one of producing large clutches and broods, and frequent breeding attempts in a habitat with a high potential carrying capacity.     

Breeding success of a Lesser Spotted Woodpecker Dendrocopos minor population

We made intensive observations of 50 pairs of Lesser Spotted Woodpecker Dendrocopos minor in southern Sweden from 1989 to 1992. Between 7% and 22% of the pairs each year defended a territory but laid no eggs. Overall, 76% of the pairs laying eggs raised fledglings, but this proportion was only 33% in 1991 when the weather was cold and wet. The mean clutch size (5.9) and brood size (4.5) in successful nests did not vary significantly between years. Incubation time was 1 day longer in 1991 (11–12 days) than in 1990 and 1992 (10–11 days). Number of young fledged per nesting attempt (3.5) and per pair (2.7) in the population also varied significantly between years. The initiation of egg laying varied between years but coincided each year remarkably well with the date when oak came into leaf. Breeding success is discussed, and comparisons are made with other hole-nesting species.     

Blood parasites in owls with conservation implications for the Spotted Owl (Strix occidentalis)

The three subspecies of Spotted Owl (Northern, Strix occidentalis caurina; California, S. o. occidentalis; and Mexican, S. o. lucida) are all threatened by habitat loss and range expansion of the Barred Owl (S. varia). An unaddressed threat is whether Barred Owls could be a source of novel strains of disease such as avian malaria (Plasmodium spp.) or other blood parasites potentially harmful for Spotted Owls. Although Barred Owls commonly harbor Plasmodium infections, these parasites have not been documented in the Spotted Owl. We screened 111 Spotted Owls, 44 Barred Owls, and 387 owls of nine other species for haemosporidian parasites (Leucocytozoon, Plasmodium, and Haemoproteus spp.). California Spotted Owls had the greatest number of simultaneous multi-species infections (44%). Additionally, sequencing results revealed that the Northern and California Spotted Owl subspecies together had the highest number of Leucocytozoon parasite lineages (n = 17) and unique lineages (n = 12). This high level of sequence diversity is significant because only one Leucocytozoon species (L. danilewskyi) has been accepted as valid among all owls, suggesting that L. danilewskyi is a cryptic species. Furthermore, a Plasmodium parasite was documented in a Northern Spotted Owl for the first time. West Coast Barred Owls had a lower prevalence of infection (15%) when compared to sympatric Spotted Owls (S. o. caurina 52%, S. o. occidentalis 79%) and Barred Owls from the historic range (61%). Consequently, Barred Owls on the West Coast may have a competitive advantage over the potentially immune compromised Spotted Owls.     

Extirpation of alternative prey during a small rodent crash

Summary We document two episodes, in different years, of Barn Owls (Tyto alba) preying on a winter population of Burrowing Owls (Athene cunicularia) on a southern California island. The predation in each case followed a marked shift in the diet of the Barn Owls, due to the cyclic decline of their normal small mammal prey. Heavy predation in the first year resulted in the extirpation of the Burrowing Owls on the island. Such heavy predation on alternative prey species is commonly reported in cyclic predator-prey systems, however this is the first documented case of extirpation of the alternative prey. Complete elimination of any prey species by terrestrial predators is, in fact, very rare.     

Aspects of the reproductive ecology of the Hamerkop Scopus umbretta in central Mali

In a 4-year study of Hamerkops in central Mali, territories of breeding pairs overlapped and most clutches were laid in the late rainy or early dry seasons. Clutches averaged 4–8 eggs. Different pairs laid eggs having, on average, different dimensions. Eggs laid in the late rainy and early dry seasons were larger than those laid at other times. Eggs weighed, at 27-8 g, about 6% of adult female weight. Hatching success was 79% with a fledging rate of eggs hatched of 53%. Successful nests fledged 27 young but for all completed clutches the fledging rate was 0'9. Young hatched early in the sequence had a higher survival rate than those hatched later. Mean age at fledging was 47 days. Pairs fledged between 0–5 and 0–9 young per year.     

Prey abundance and reproductive success of the golden eagle Aquila chrysaetos in Sweden

Reproductive output of the golden eagle Aquila chrysaetos (L.), was studied in two areas within the species distribution in northern Sweden during 1975–1980. Reproductive success was compared with the abundance (based on hunting bag statistics) of small game prey species and with the microtine cycles. The proportion of golden eagle pairs with successful breeding and the number of young produced per occupied territory varied greatly between years (21–85% and 0.27–1.24, respectively). In the northern study area I found a significant correlation between the proportion of pairs with successful breeding versus total hunting bag of small game species. There were also significant correlations between vole density and breeding success one year later. This was not the case in the southern study area, mainly due to a good reproductive year for golden eagles in 1977 when small game species were scarce. The good reproductive output in 1977 may be explained by favourable weather conditions that spring. Whether breeding occurs or not is probably determined by prey abundance early in spring just before the golden eagle female lays her eggs.     

Costs and benefits of breeding in human-altered landscapes for the Eagle Owl Bubo bubo

We studied a population of 23–25 Eagle Owl Bubo bubo pairs between 1994 and 2000 in a 1330-km² study plot in the central-eastern Italian Alps. Compared to random sites, territories were located at lower elevation and closer to intensively cultivated-urbanized valley floors. Early laying was associated with low elevation and negatively affected productivity. Diet was dominated by rats, hedgehogs and dormice ( n  = 978 prey items), all of them typical of low-elevation habitats. Higher productivity was associated with a higher proportion of rats in the diet of individual pairs. Low availability of rats resulted in a more diverse diet, in turn associated with low productivity. Territories were occupied every year in a non-random fashion, and those most occupied were characterized by higher productivity and higher occurrence of the favoured prey types in the diet, suggesting they were of superior quality. Eagle Owls also paid a cost associated with nesting near human-altered habitats: the main cause of mortality reported to local authorities was electrocution. This is an increasing cause of death for many European populations and may be a cause for conservation concern. Human persecution is also an important cause of mortality in some parts of the European range. Apart from such costs, the study population appeared to have adapted well to the proximity of humans: estimates of density and productivity were comparable to those recorded elsewhere in Europe. The pattern found in our population also held at higher spatial scales: data from 17 European populations showed density to be highest in low-elevation, human-altered landscapes.     

The distribution and population of the Seychelles (Bare-legged) Scops Owl Otus insularis on Mahé: consequences for conservation

This study details the first baseline survey of the Critically Endangered Seychelles Scops Owl Otus insularis , currently only recorded from the 152-km² island of Mahé, the largest and highest island in the granitic Seychelles, western Indian Ocean. A survey was conducted in October 2000–March 2001 using playback of conspecific calls in random squares (500 m × 500 m) with midpoints being at least equal to 100 m asl. Playback was conducted in 159 of a possible 375 squares (42%). Territorial responses were detected in 60 of 159 (38%) squares, which represented an estimated 70 distinct territorial responses. Pairs responded in 51% and single birds responded in 49% of squares where a response was elicited. Scops Owls were more likely to be detected at higher altitudes, in mixed forest, and sympatrically with endemic frogs ( Tachycnemis seychellensis and Sooglossus spp.). Two models were used to predict population: one based exclusively on altitude resulted in a population estimate of 134–159 territories (268–318 individuals) within a 34-km² range, whereas a second incorporating altitude and vegetation, which excluded unsuitable habitat, resulted in an estimate of 125–142 territories (250–284 individuals) in a 31-km² range. We discuss the implications of our findings to the Owl's conservation status and management.     

The breeding biology and causes of nest failure of Scottish Black-throated Divers Gavia arctica

The breeding biology and causes of nest failure were examined for Black-throated Divers Gavia arctica in core areas of their Scottish breeding range in 1983–1987. Breeding was confirmed for up to 88% of territorial pairs each year ( n = 28–62), and 76% of nests were on islands. Hatching success was consistently low with, on average, only 43% of territorial pairs managing to hatch a clutch each year; 64% of recorded nest failures occurred during the first week of the 4-week incubation period.
Overall breeding success in West Sutherland in 1984–1987 averaged 0.23 chicks per territorial pair per year, while in Ross-shire for 1986–1987 it was 0.29. Forty percent of hatched chicks survived to fledge, and 92% of recorded deaths occurred in the first fortnight after hatching; 4.8% of fledged broods held two chicks.
Causes of nest failure were assessed with the aid of surveillance cameras. Approximately 30% of losses were due to water level changes (mostly floods), 48% to predators (primarily nocturnal mammals, but also Hooded Crows Corvus corone ), 13% to human egg collectors and 5% to desertion following human disturbance.
Scottish Black-throated Divers produce only half the number of chicks tentatively estimated to be required to maintain a stable population. The main difference between the Scottish and more successful Swedish populations is in the degree of chick mortality.     

Impact of food abundance, diet and food quality on the breeding of the fruit pigeon, Parea Hemiphaga novaeseelandiae chathamensis, on Chatham Island, New Zealand

Breeding and diet of Parea Hemiphaga novaeseelandiae chathamensis were studied in relation to food abundance and quality on Chatham Island from 1991 to 1994. Although pairs were found breeding in all months, they nested predominantly during winter and spring (June-November). The timing of the nesting season, the proportion of pairs that bred and the number of chicks reared per pair varied between nesting seasons. During the 1992–1993 and 1994–1995 nesting seasons, all pairs nested, and many pairs reared two chicks, often involving clutch overlap (58% of 12 cases in 1992–1993, 37% of eight cases in 1994–1995). In 1993–1994, when fruit was scarce, nesting began 2 months later, only 44% of pairs nested and no pairs attempted to rear a second chick. Prior to and during the productive nesting seasons (1992–1993, 1994–1995), the diet of Parea consisted mainly of fruit, particularly that of Matipo Myrsine chathamica in autumn (March-May) and Hoho Pseudopanax chathamicus in winter and spring. Nutrient analyses of the main Parea foods showed that the pulp of these fruit were rich in lipids and available carbohydrates compared with those in foliage foods. Heavy fruiting of Matipo and Hoho promoted early nesting and prolonged nesting for 6 months, including nesting during winter.     

Mortality causes in British Barn Owls Tyto alba, with a discussion of aldrin-dieldrin poisoning

During 1963-89, 627 Barn Owl Tyto alba carcasses were received for autopsy and chemical analysis. Much larger numbers were received per month outside the breeding season than within it, with peaks in autumn (mainly juveniles) and late winter (adults and juveniles).
The main causes of recorded deaths were collisions (mostly with road traffic) and starvation. No great seasonal variation occurred in the main causes of recorded deaths and starved juveniles were reported even in summer. Most starved males weighed less than 240 g, and most starved females less than 250 g.
Another important cause of mortality in eastern arable counties, at least to 1977, was poisoning by organochlorine pesticides, especially aldrin/dieldrin. Levels of HEOD (the metabolized product of aldrin/dieldrin) in the livers of birds that had apparently died of aldrin/ dieldrin poisoning were in the range 6–44 ppm (geometric mean 14 ppm). Pesticide victims formed up to 40% of all dead Barn Owls obtained from some eastern counties during 1963-77. By 1987-89, HEOD levels in Barn Owls in eastern counties had fallen to less than 1.6 ppm, and no deaths from organochlorine poisoning were recorded.
Organochlorine pesticides almost certainly contributed to population decline in eastern England evident in the 1950s and 1960s, and reductions in the use of these chemicals may have allowed a subsequent increase, apparent over the last 10–15 years.     

Larval sensory abilities and mechanisms of habitat selection of a coral reef fish during settlement

In most animals, siblings from a given reproductive event emerge over a very short period of time. In contrast, many species of birds hatch their young asynchronously over a period of days or weeks, handicapping last-hatched chicks with an age and size disadvantage. Numerous studies have examined the adaptive significance of this atypical hatching pattern, but few have attempted to explain the considerable intrapopulation variation that exists in hatching asynchrony. I explored proximate determinants of hatching asynchrony by monitoring 112 Burrowing Owl (Athene cunicularia) nests in the grasslands of southern Saskatchewan, Canada, over 4 years. Age disparities between first- and last-hatched siblings (i.e., hatching spans) varied considerably, ranging between 1 and 7 days (mode = 4 days). These hatching spans increased with increased hatching success. Hatching spans also increased with larger clutches, but the increase was less than predicted given the increased time required to lay more eggs. Hatching span was unrelated to number of prey cached in the nest during egg laying (an index of food availability), and was unaltered by a year of super-abundant prey. Furthermore, pairs given extra food during laying had hatching spans equal to those of unsupplemented control pairs. These results were inconsistent with both the energy constraint and facultative manipulation hypotheses, which predict that hatching asynchrony should vary with the level of food during laying, when incubation onset is determined. Burrowing Owls were apparently free of food limitation early in breeding, yet may not have been able to optimize hatching spans because food conditions during laying were largely unrelated to food conditions during brooding. Thus, one of the premises for facultative manipulation of hatching asynchrony—that laying females are able to forecast post-hatch food conditions—may not have been met for this population of Burrowing Owls.     

南充高坪机场短耳 鸮 越冬期的食性分析和习性观察

2006年3～5月,收集南充高坪机场草地和周围松林越冬期短耳鸮(Asio flammeus)的食团,进行食性分析。在805个完整食团和一些零碎的食团中,小型兽类是短耳食物组成的主要成分,占98.4%,其中四川短尾(Anourosorex squamipes)所占比例最高,为97.2%。通过调查短耳鸮的食团在南充高坪机场草地里的分布情况,分析短耳v在机场草地的栖息地选择,发现短耳鸮并没有选择草高和密集的区域作为栖息场所,而高20cm左右的白茅(Imperata cylindrical)丛是短耳最喜欢栖息的场所。     

Factors affecting spontaneous vocal activity of Tawny Owls Strix aluco and implications for surveying large areas

To use vocalizations properly for the estimation of owl population size, it is important to identify how environmental factors affect owl calling behaviour. Here, we analyse how intrinsic and extrinsic factors modify the vocal activity of Tawny Owls Strix aluco in two areas of northern Spain. From March 2013 to May 2015, we radiotracked 20 Tawny Owls and also undertook a systematic survey in which we collected data on spontaneous vocal activity (hoot/call) of the tagged owls, plus their mates and neighbours (36 untagged owls). After 223 nights in Valle de Mena and 224 in Duranguesado we obtained a total of 8791 records of vocal activity. The annual proportion of surveys on which an owl called was 6.3% and did not differ between the study areas. Vocal activity of Tawny Owls varied with sex, annual cycle stage and weather. Male owls were significantly more vocal than females year‐round, and vocal activity peaked during the incubation and post‐breeding periods. Wind and rain adversely affected vocal activity of both sexes throughout the year. Tagged owls were detected more often than untagged owls, which we interpret as an observer effect because the systematic survey ensured that short distances to tagged owls increased the probability of detecting vocal activity. In fact, 2.8% of variation in vocal activity was due to detectability differences between tagged and untagged owls. We conclude that if fieldwork is carried out during the optimum period of the year for vocal detection (i.e. incubation, which in our case was around mid‐April), and under good weather conditions (dry and calm nights), censuses based on spontaneous vocal activity would detect only approximately 12% of the true Tawny Owl population.     

Survey of blood parasites in two forest owls, Northern Saw-whet Owls and Flammulated Owls, of western North America

Except for a few studies in the eastern United States, little has been published on hemoparasites in owls. We surveyed the blood parasites of 108 Northern Saw-whet Owls (Aegolius acadicus) and 24 Flammulated Owls (Otus flammeolus) in Idaho during autumn migration in 1999 and 2000. We also surveyed 15 Flammulated Owls (FLOW) during breeding season in Utah from 2000. Leucocytozoon ziemanni, Haemoproteus syrnii, Haemoproteus noctuae, and Trypanosoma avium were identified. The overall prevalence of infection was 53% (78/147) and for the combined species, prevalences of Haemoproteus, Leucocytozoon, and Trypanosoma species were 20%, 39%, and 4%, respectively. Northern Saw-whet Owls (NSWO) had an overall prevalence of 51% (55/108), with prevalences of 6%, 47%, and 4% by hemoparasite genus, respectively. Flammulated Owls had an overall prevalence of 59% (23/39), with prevalences of 56%, 18%, and 5% by genus, respectively. This study provides baseline hematozoa information for two boreal owl species.     

Seasonal variation of territory size with the Little Owl (Athene noctua)

Summary In a population of Little Owls (Athene noctua) at the Lower Rhine (FRG), the factors were studied that influence the size and shape of territories of this non-migrating, all-year territorial owl species. These studies were carried out between September 1984 and June 1987. The birds were individually marked with transmitter packages so that their locomotional movements could be monitored. Using a standard protable stimulus (a dummy with an attached loudspeaker) the territorial boundaries of 19 male Little Owls were surveilled during the different seasons of the year. Male Little Owls defended their territories in all seasons, but distinct seasonal changes of intraspecific aggressiveness and territory size were observed. The seasonal variations of territory size followed a common pattern in all studied Little Owls, in spite of individual differences in the size of the defended areas. The largest territories were defended in March/April during the courtship season . In May/June all male Little Owls reduced the size of their territories . This corresponds to the breeding and nestling period. The yearly minimum of territory size was reached in the summer months July and August when the fledglings were still fed in the parental territory. When the first-year birds started to disperse in autumn (September/October), the size of the defended areas of the adult tenants again increased . In winter (November to February), a further increase in territory size was observed for periods of warm weather . Male Little Owls, however, were less aggressive during winter than in the following courtship season. On cold winter days with a ground cover of snow territorial aggressiveness ceased. Pastures and meadows offered a continuous food supply almost throughout the year. In some seasons they were overproportionally represented in the territories of Little Owls compared to the general surroundings. In reaction to changing accessibility of food, the hunting ranges within the home ranges were shifted much faster than the boundaries of the defended territories. The significance of various factors contributing to the variability of territory size in Little Owls are discussed (e.g. availability of food, seasonal and individual differences in aggressiveness, experience in the occupied area, population density).     

The status of breeding Barn Owls Tyto alba in the United Kingdom 1995–97

A national survey of breeding Barn Owls was undertaken between 1995 and 1997 using intensive fieldwork methods within a stratified sample of 1100 2 × 2-km survey squares selected at random from those available. Each year, fieldwork was divided into two sessions: one to locate potential nest-sites (winter session) and one to determine occupancy of these sites (summer session). Fieldworkers spent an average of 30 hours on fieldwork within each survey square. The survey produced national population estimates of 2830 (95% confidence intervals: 1952–3761) breeding pairs for 1995, 3967 (95% CI: 2785–5252) for 1996 and 3951 (95% CI: 2769–5214) for 1997. Analysis taking account of the poor coverage in certain regions of high Barn Owl density in 1995 suggests that a population estimate of 3480 would be more accurate for that year. Regional and temporal variations in estimates were examined and interpreted in relation to Barn Owl productivity and ecology. Validation of fieldwork efficiency was carried out within a random selection of the available survey tetrads, demonstrating that fieldworkers achieved a high degree of survey reliability. This paper provides a baseline population estimate and standardized, repeatable methods, allowing future population changes to be monitored effectively.     

Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre‐breeding food conditions and winter severity on between‐year variations in population size and reproductive performance. To estimate pre‐breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.