Constraints on the coding of sound frequency imposed by the avian interaural canal

Summary Extracellular recordings were made from the midbrain auditory area to determine the limits of auditory frequency sensitivity in a variety of birds. The audiograms of some species show a consistent missing frequency range of 1/3 to 1/2 an octave, to which no neurons are tuned. All species, except owls, have a low upper frequency limit in comparison with mammals of similar headwidth. A consideration of both the upper frequency limits and the missing frequency ranges led to the conclusion that frequencies which do not generate localization cues are not represented in the midbrain. The upper frequency limit appears to match the upper limit of generation of significant interaural and monaural intensity cues to localization. The variation of these cues with frequency was examined through a simple model of the birds' sound receiving system which incorporated the interaural canal and considered the tympanic membranes as pressure difference receivers. Apart from coraciiform species, which have low upper frequency limits matching the frequency of the primary missing frequency band of other species, and owls, which have high upper frequency limits, the upper frequency limits of the birds studied are inversely related to head-width.The argument for missing frequency ranges being related to nonlocalizable frequencies is simpler, for it has been found previously, using cochlear microphonic recording, that within a bird's audiogram there are frequency regions with poor directionality cues. These regions appear to correspond to the missing frequency ranges.Abbreviation nMLD nucleus mesencephalicus lateralis dorsalis     

Magnetoreception and its use in bird navigation

Recent advances have brought new insight into the physiological mechanisms that enable birds and other animals to use magnetic fields for orientation. Many birds seem to have two magnetodetection senses, one based on magnetite near the beak and one based on light-dependent radical-pair processes in the bird's eye(s). Among the most exciting recent results are: first, behavioural responses of birds experiencing oscillating magnetic fields. Second, the occurrence of putative magnetosensory molecules, the cryptochromes, in the eyes of migratory birds. Third, detection of a brain area that integrates specialised visual input at night in night-migratory songbirds. Fourth, a putative magnetosensory cluster of magnetite in the upper beak. These and other recent findings have important implications for magnetoreception; however, many crucial open questions remain.     

The relationship between intra–guild diet overlap and breeding in owls in Israel

Even though intra-guild predators frequently prey on the same species, it is unclear whether diet overlap between two predators is a source of interspecific competition or whether predators simply use the same abundant prey resource. We measured the extent to which the diets of barn owls (Tyto alba) and long-eared owls (Asio otus) in Israel overlap and examined whether yearly differences in diet overlap correlate with barn owl breeding success. Pianka’s index of niche overlap was positively related to barn owl population size but not to its breeding success. The number of breeding barn owls was higher when long-eared owls consumed more rodents, suggesting that diet overlap most likely increased when rodents became more abundant. Therefore, in Israel, when these two owl species prey more often on rodents, their diets are more similar and interspecific competition is reduced. Unlike sympatric populations in Europe, in years when rodents are less abundant in Israel long-eared owls switch to hunting alternative prey (e.g., birds), perhaps to avoid competition with barn owls.     

Helminth Communities of Owls (Strigiformes) Indicate Strong Biological and Ecological Differences from Birds of Prey (Accipitriformes and Falconiformes) in Southern Italy

We compared the helminth communities of 5 owl species from Calabria (Italy) and evaluated the effect of phylogenetic and ecological factors on community structure. Two host taxonomic scales were considered, i.e., owl species, and owls vs. birds of prey. The latter scale was dealt with by comparing the data here obtained with that of birds of prey from the same locality and with those published previously on owls and birds of prey from Galicia (Spain). A total of 19 helminth taxa were found in owls from Calabria. Statistical comparison showed only marginal differences between scops owls (Otus scops) and little owls (Athene noctua) and tawny owls (Strix aluco). It would indicate that all owl species are exposed to a common pool of ‘owl generalist’ helminth taxa, with quantitative differences being determined by differences in diet within a range of prey relatively narrow. In contrast, birds of prey from the same region exhibited strong differences because they feed on different and wider spectra of prey. In Calabria, owls can be separated as a whole from birds of prey with regard to the structure of their helminth communities while in Galicia helminths of owls represent a subset of those of birds of prey. This difference is related to the occurrence in Calabria, but not Galicia, of a pool of ‘owl specialist’ species. The wide geographical occurrence of these taxa suggest that local conditions may determine fundamental differences in the composition of local communities. Finally, in both Calabria and Galicia, helminth communities from owls were species-poor compared to those from sympatric birds of prey. However, birds of prey appear to share a greater pool of specific helmith taxa derived from cospeciation processes, and a greater potential exchange of parasites between them than with owls because of phylogenetic closeness.     

The organization, control and coordination of measures for localization and liquidation of mass poultry loss and prevention of human diseases caused by avian flu in Ordynsk area of Novosibirsk region

Materials on the organization, the control and to coordination of actions of services in carrying out of actions on localization and liquidation of the centers of a mass destruction of birds and preventive measures of people diseases by avian flu during the period from July, 21 till September, 18, 2005 are submitted. The basic actions which have been carried out by a territorial department, the quarantine of poultry excluding contact with wild birds, depopulation of a sick and suspicious birds on disease and disinfection in the foci of a mass case, including installation disinfection barriers, etc. As a result of spent actions the bird's mass destruction has been stopped, quarantine is taken off 10.11.2005. The conclusion is made, that due to carrying out sanitary-preventive and antiepidemic measures it is possible not only to locate, but also completely to liquidate a mass destruction of birds.     

Influence of bill and foot morphology on the ectoparasites of barn owls

Preening is the principle behavioral defense used by birds to combat ectoparasites. Most birds have a small overhang at the tip of their bills that is used to shear through the tough cuticle of ectoparasitic arthropods, making preening much more efficient. Birds may also scratch with their feet to defend against ectoparasites. This is particularly important for removing ectoparasites on the head, which birds cannot preen. Scratching may be enhanced by the comb-like serrations that are found on the claws of birds in many avian families. We examined the prevalence and intensity of ectoparasites of barn owls (Tyto alba pratincola) in southern Idaho in relation to bill hook length and morphological characteristics of the pectinate claw. The barn owls in our study were infested with 3 species of lice (Phthiraptera: Ischnocera): Colpocephalum turbinatum , Kurodaia subpachygaster, and Strigiphilus aitkeni . Bill hook length was associated with the prevalence of these lice. Owls with longer hooks were more likely to be infested with lice. Conventional wisdom suggests that the bill morphology of raptors has been shaped by selection for efficient foraging; our data suggest that hook morphology may also play a role in ectoparasite defense. The number of teeth on the pectinate claw was also associated with the prevalence of lice. Owls that had claws with more teeth were less likely to be infested with lice, which suggests that larger pectinate claws may offer relatively more protection against ectoparasitic lice. Experiments that manipulate the bill hook and pectinate claw are needed to confirm whether these host characters are involved in ectoparasite defense. Finally, we recovered mammalian ectoparasites from 4 barn owls. We recovered species of mammalian lice (Phthiraptera:Anoplura) and fleas (Siphonaptera) that are commonly found on microtine rodents. The owls probably acquired these parasites from recently eaten prey. This represents 1 of the few documented cases of parasites "straggling" from prey to predator.     

Movement and direction of movement of a simulated prey affect the success rate in barn owl Tyto alba attack

The present study was aimed at testing a novel idea, that rather than maximizing their distance from a predator during close-distance encounters, prey species are better off moving directly or diagonally toward the predator in order to increase the relative speed and confine the attack to a single available clashing point. We used two tamed barn owls Tyto alba to measure the rate of attack success in relation to the direction of prey movement. A dead mouse or chick was used to simulate the prey, pulled to various directions by means of a transparent string during the owl's attack. Both owls showed a high success rate in catching stationary compared with moving food items (90% and 21%, respectively). Success was higher when the prey moved directly away, rather than towards the owls (50% and 18%, respectively). Strikingly, these owls had 0% success in catching food items that were pulled sideways. This failure to catch prey that move sideways may reflect constraints in postural head movements in aerial raptors that cannot move the eyes but rather move the entire head in tracking prey. So far there is no evidence that defensive behavior in terrestrial prey species takes advantage of the above escape directions to lower rates of predator success. However, birds seem to adjust their defensive tactics in the vertical domain by taking-off at a steep angle, thus moving diagonally toward the direction of an approaching aerial predator. These preliminary findings warrant further studies in barn owls and other predators, in both field and laboratory settings, to uncover fine predator head movements during hunting, the corresponding defensive behavior of the prey, and the adaptive significance of these behaviors.     

链霉素对鸟听觉毒性作用的研究

目的：了解链霉素对鸟听觉毒性的作用。方法：选33只健康成年虎皮鹦鹉,不同剂量的链霉素肌肉注射15日,脑干听觉诱发电位测试外周的听觉敏度和听觉通路中神经的传导和传递能力。结果：链霉素对鸟听觉有毒性作用。结论：用链霉素处理鸟可以制作聋鸟模型。     

Migratory birds use head scans to detect the direction of the earth's magnetic field

Night-migratory songbirds are known to use a magnetic compass , but how do they detect the reference direction provided by the geomagnetic field, and where is the sensory organ located? The most prominent characteristic of geomagnetic sensory input, whether based on visual patterns or magnetite-mediated forces , is the predicted symmetry around the north-south or east-west magnetic axis. Here, we show that caged migratory garden warblers perform head-scanning behavior well suited to detect this magnetic symmetry plane. In the natural geomagnetic field, birds move toward their migratory direction after head scanning. In a zero-magnetic field , where no symmetry plane exists, the birds almost triple their head-scanning frequency, and the movement direction after a head scan becomes random. Thus, the magnetic sensory organ is located in the bird's head, and head scans are used to locate the reference direction provided by the geomagnetic field.     

Optimal stopover decisions under wind influence: the effects of correlated winds

Wind speed and direction have a significant effect on a flying bird's ground speed. Migrants are therefore expected to be sensitive to wind conditions and this should have consequences for optimal strategies of stopover and refuelling. Based on an earlier model of time-minimizing migration which includes wind condition, we investigate the consequences of the temporal correlation of wind conditions. Day-to-day changes in wind conditions are modelled with a two-state Markov process and an expression for the expected speed of migration is derived. The policy of the migrants is described by two parameters: a day t(g) when the birds start to leave whenever favourable conditions occur and a later day t(b)when they leave even in unfavourable winds. The model predicts that in most cases departures should be close to the date which is predicted by a wind-free deterministic model and that the birds should never leave without wind assistance. Only if the probability that the condition remains the same on the following day is close to 1 should the birds leave even in unfavourable conditions shortly after the deterministic optimal date. If the transition matrix is highly asymmetrical, i.e. if it is very probable that unfavourable conditions remain and that favourable conditions will change into unfavourable, then the birds are predicted to start using good winds several days before the deterministic optimal date. An analysis of six years of wind data from two sites in Sweden shows that wind directions on successive days are in fact correlated in all years.     

Variation in the male territorial hoot of the Tawny Owl Strix aluco in three English populations

Little is known about owl song. We made sonagrams of the territorial calls of 50 male Tawny Owls Strix aluco from three different areas. Six temporal and four frequency measures of the calls were recorded from the sonagrams. The measures of the calls were then subjected to analysis to try to separate between individual owls and between owls from different areas. We also looked for similarities between calls of neighbouring owls and for any effect of habitat on owl hoots. Individual owls were separated on the basis of their hoots with a high degree of success (98.6% overall), and there were significant differences between areas. Differences were found between calls in woodland and farmland habitats, but these differences were not in the direction expected to increase sound transmission. Calls of neighbouring owls did not resemble each other more than calls from owls that were not in vocal contact, implying that if calls are learned by Tawny Owls, they are learned before dispersal.     

NOTES ON THE ECOLOGY OF THE CATTLE EGRET ARDEOLA IBIS AT ROKUPR, SIERRA LEONE

SUMMARY
The Cattle Egret is a dry season visitor to Rokupr in Sierra Leone during the bird's non-breeding season. There are no cattle in the area to attract the herons and they obtain nearly all their food from small isolated areas of vegetable gardens which are associated with all the villages. The number of herons associated with each garden is closely correlated with the area of that garden and is about two birds per acre.
The daily life of the birds is discussed, in particular the pre-roosting assemblies and the flight to roost, and it is shown that each flock leaves for the roost at the same time each day, about 30–35 min. before dusk.
Observations made at a particular roost showed that all the Cattle Egrets reached the roost before dusk and from these observations, combined with those made on the feeding grounds, it is concluded that the number of Cattle Egrets using the roost is determined by the number and area of the feeding grounds that lie within 30–35 minutes flying time (about 12 miles) of the roost.
Other species using the roost are briefly discussed.     

Assessing students’ knowledge of owls from their drawings and written responses

Many children learn about and experience animals in the everyday environment where they live and attend school. One way to obtain information about children’s understanding of concepts or phenomena is by using their drawings in combination with written responses or interviews. This study assesses how much Slovenian students 10–15 years old (in sixth to ninth grade) know about owls by analysing their drawings and written responses. The study included 473 students. From assessing students’ drawings and written responses, it can be concluded that the respondents had some knowledge of owls’ appearance, their behaviours, diet and habitats. The differences between students in different grades regarding the representations of owls was not statistically significant. Some students had misconceptions about owls, such as the idea that owls can turn their heads 360 degrees, or they confused the long ear-tufts with external parts of the ears. The students’ written responses provided additional information on their ideas about owls; particularly about owls’ specific behaviours, diet, and conservational status. However, some information, such as depicting owls’ body parts and body proportions or their habitats, was more clearly depicted with drawings. One third of the students drew owls in trees and forests, which makes owls good candidates for promoting forest conservation.     

An additional bone in the sclera of the eyes of owls and the common potoo (Nictibius griseus) and its role in the contraction of the nictitating membrane

Morphometric, anatomical and histological examinations were made in 10 species of owls of the families Tytonidae and Strigidae and compared with the eyes of other species of nocturnal birds including common potoo (Nictibiidae) and three species of nightjars (Caprimulgidae) and two diurnal species: the roadside hawk (Accipitridae) and the domestic duck (Anatidae). In owls and the common potoo the nictitating membrane is situated on the dorsal edge of the eye. In these birds, the scleral ring bears an additional, previously undescribed bone of various forms and dimensions (1.4-6.8 mm of length and 0.8-3.3 mm of width), located on the trajectory of the tendon of the pyramidal muscle which is attached to the nictitating membrane. This bone has a groove that encloses the tendon of the pyramidal muscle, preventing it from separating from the sclera during contraction, as well as diverting the trajectory of the tendon to impede it from projecting itself over the cornea. In the ferruginous pygmy owl, Nacunda nighthawk, Pauraque, scissor-tailed nightjar, roadside hawk and domestic duck the additional bone was not seen. Based on the morphofunctional characteristics of the bone, we suggest that this bone should be named the scleral sesamoid bone.     

Factors associated with returns of snowy owls to airports following translocation

Human-dominated environments often include ecological traps for wildlife, such as airports that may be perceived as suitable habitat by grassland birds but reduce fitness because of collisions with aircraft. Birds of prey are often attracted to airports where collisions with aircraft (i.e., bird strikes) are usually fatal for the birds and are a significant threat to flight safety. The snowy owl (Bubo scandiacus) is known for its nomadism, exhibiting unpredictable and highly variable movements during the nonbreeding season, including being a common visitor to airports, which often have high small-mammal populations and mimic flat, open habitats used naturally by owls. Since 2009, the Federal Aviation Administration reported an average of 22 snowy owl deaths annually due to aircraft collisions throughout 55 North American airports. To aid in active management of owls at airports, we assessed relocation data of 42 telemetry-tracked snowy owls from 2000–2020 in the United States and Canada. Owls that returned to the airport after relocation (33%) frequently crisscrossed and perched near runways where they were at risk of strikes. Adult females and immature males were more likely to return than the other sex and age classes, and returns were less likely to occur as the distance between the release site and the airport increased. Owls relocated in open habitats with a greater proportion of wetland and cropland (including grasslands and pasture) land cover classes were also less likely to return. We conclude that inclusion of multiple factors to limit return rates of relocated snowy owls from airport facilities can unspring the ecological trap presented by airports to these owls.     

OBSERVATIONAL LEARNING IN THREE SPECIES OF BIRDS

White-throated Sparrows Zonotrickia albicollis, Fork-tailed Flycatchers Muscivora tyrannus and Black-capped Chickadees Porta atricapillus were placed in experimental situations where they could watch a trained companion uncover a hidden mealworm. After a period of watching its companion find the concealed mealworm, the observer bird was isolated visually from the other bird. While in isolation the observer birds approached, touched and pecked at a hidden food tray significantly more often than control birds which had not had an opportunity to observe a trained companion. However, the experimental birds failed to learn from observation alone how to uncover the concealed mealworm. But if rewarded in the presence of the companion bird (by taking a mealworm from it or by uncovering a mealworm as a result of local enhancement), then the observer bird frequently did come to find the prey in isolation. It is suggested that the interaction between observational learning and a bird's reinforced socially facilitated experience could assist in the development and expansion of a bird's behavioural repertoire.     

RECENT BIOACOUSTIC PUBLICATIONS (2002 and earlier)

To more easily and non-invasively monitor urban Eastern Screech-Owl populations, we developed a method of distinguishing individual owls using their calls. A set of seven variables derived from recordings of ‘bounce’ calls taken from 10 known (either free-ranging birds recorded at a single site on a single night or identifiable captive owls) owls was tested using a model-based clustering analysis (Mclust) as a method of discriminating individual owls. The cluster analysis correctly classified these calls with 98% accuracy. A second set of calls from nine owls was used to further test the method and correctly classified 84% of the calls using the same variables. Four owls were recorded repeatedly from 2008 to 2010 to determine the extent to which calls changed over time; the cluster analysis correctly assigned 89% of the calls to the correct owl regardless of the year the recordings were made. Based on these results, we are confident that the Mclust analysis can be used to reliably and safely estimate abundance and survival of Eastern Screech-Owls within the time frame of a few years and of population sizes < 15 owls.     

Comparison of Species-Specific Bird Signals and Human Speech

We carried out a comparative study of spectral-prosodic characteristics of bird vocalization and human speech. Comparison was made between the relative characteristics of the fundamental frequency and spectral maxima. Criteria were formulated for the comparison of bird's signals and human speech. A certain correspondence was found between the vocal structures of birds and humans. It was proposed that in the course of evolution, man adopted the main structural principles of his acoustic signalling from birds.     

Optimal moult strategies in migratory birds

Avian migration, which involves billions of birds flying vast distances, is known to influence all aspects of avian life. Here we investigate how birds fit moult into an annual cycle determined by the need to migrate. Large variation exists in moulting patterns in relation to migration: for instance, moult can occur after breeding in the summer or after arrival in the wintering quarters. Here we use an optimal annual routine model to investigate why this variation exists. The modelled bird's decisions depend on the time of year, its energy reserves, breeding status, experience, flight feather quality and location. Our results suggest that the temporal and spatial variations in food are an important influence on a migratory bird's annual cycle. Summer moult occurs when food has a high peak on the breeding site in the summer, but it is less seasonal elsewhere. Winter moult occurs if there is a short period of high food availability in summer and a strong winter peak at different locations (i.e. the food is very seasonal but in opposite phase on these areas). This finding might explain why only long-distance migrants have a winter moult.     

Migratory decisions in birds: extent of genetic versus environmental control

Migration is one of the most spectacular of animal behaviors and is prevalent across a broad array of taxa. In birds, we know much about the physiological basis of how birds migrate, but less about the relative contribution of genetic versus environmental factors in controlling migratory tendency. To evaluate the extent to which migratory decisions are genetically determined, we examined whether individual western burrowing owls (Athene cunicularia hypugaea) change their migratory tendency from one year to the next at two sites in southern Arizona. We also evaluated the heritability of migratory decisions by using logistic regression to examine the association between the migratory tendency of burrowing owl parents and their offspring. The probability of migrating decreased with age in both sexes and adult males were less migratory than females. Individual owls sometimes changed their migratory tendency from one year to the next, but changes were one-directional: adults that were residents during winter 2004–2005 remained residents the following winter, but 47% of adults that were migrants in winter 2004–2005 became residents the following winter. We found no evidence for an association between the migratory tendency of hatch-year owls and their male or female parents. Migratory tendency of hatch-year owls did not differ between years, study sites or sexes or vary by hatching date. Experimental provision of supplemental food did not affect these relationships. All of our results suggest that heritability of migratory tendency in burrowing owls is low, and that intraspecific variation in migratory tendency is likely due to: (1) environmental factors, or (2) a combination of environmental factors and non-additive genetic variation. The fact that an individual’s migratory tendency can change across years implies that widespread anthropogenic changes (i.e., climate change or changes in land use) could potentially cause widespread changes in the migratory tendency of birds.