Bird Predation Research Articles

Harvesting model for fishery resource with reserve area of bird predator and modified effort function

Harvesting model for fishery resource with reserve area of bird predator and modified effort function

A Model Explaining Infantile Esotropia: Dissociated Strabismus as a Result of Sensory Interhemispheric Dissociation and Crossed Dominance in the Brainstem

Over 150 million years, modern reptiles, birds and mammals evolved. Predatory birds and mammals have eyes on the front of their heads. In these animals, binocular correspondence, voluntary eye movements, eye-hand coordination, partial decussation at the optic chiasm and cortical interhemispheric pathways could develop at the cost of a smaller visual field. The subsequent enlargement of the cerebral neocortex and the hemispheric pathways are of central importance in binocular vision, sensory fusion and infantile strabismus. To investigate visual interhemispheric fibers, tractography was used in subjects with infantile esotropia (IE), callosal agenesis and control subjects with normal binocularity. In human callosal agenesis, normal binocularity could be explained by a different interhemispheric connection. In subjects with infantile esotropia, the analyses starting from the primary visual area on one side appeared different from the analysis from the other side. The distribution areas are asymmetrical between sides. Binocularity and alignment not only rely on correspondence between crossed and uncrossed hemi-representations but, in addition the corpus callosum, the most important interhemispheric pathway in placental mammals, seems important in the development of human binocularity. When correspondence is possible between the hemi-representations of the crossed and the uncrossed pathway on both sides of the cortex, the uncrossed pathway finds its way via the corpus callosum toward the contralateral hemi-representation of the same eye. A vertical midline must come out of this process. Meanwhile, however, the other uncrossed pathway strives to find the vertical midline of the other eye. Likely, the corpus callosum is important during the tuning of the pathways involved in sensory fusion. The anterior commissure might be an alternative in callosal agenesis. A failure in the offset will result in strabismus and crossed dominance after V1. Consequently, the normal binocular development of the brainstem (i.e., the superior colliculus), will not take place and latent nystagmus, as well as dissociated divergence, may ensue.

People power reveals starling secrets

Before coming down to roost, starlings regularly flock together in murmurations of thousands of individual birds moving in synchrony, creating one of nature's most impressive aerial displays. This sight has piqued the curiosity of many scientists across different fields and, as a result, we know how these murmurations function, with each bird following the movements of their six or seven nearest neighbours. Despite this, we still don't know why starlings come together in such large numbers.There are two hypotheses that attempt to explain this behaviour: the ‘warmer together’ hypothesis, which suggests that starlings gather to advertise a roost site, with the roost becoming warmer as more birds join; and the ‘safer together’ hypotheses, suggesting that large murmurations confuse predators, make individual birds harder to pinpoint and attack, and simply reduce the chances of any one individual being preyed upon.A team of researchers, headed by Anne Goodenough at the University of Gloucestershire, UK, harnessed the power of citizen science to try and determine which of these is the case. They sent out surveys to members of the public asking for details of murmuration sightings from across the UK, as well as several other countries. In addition to the location, respondents were asked to estimate the number of birds present and the duration of the murmuration event, to log how it ended (did the birds go to roost or disperse?), the temperature and the presence of other birds, namely predatory species – such as kestrels, sparrowhawks and buzzards – and corvids and gulls, which when silhouetted could be mistaken for predatory species.From these surveys, over 3200 records of starling murmurations were collected. By putting the different variables together in a model, the team could analyse which were correlated with murmuration size. They found that the temperature was not significantly linked to the number of starlings in a murmuration; however, the presence of predatory birds was positively associated with larger murmurations, providing evidence for the safer together hypothesis. Interestingly, murmuration size was not linked to the presence of gulls or corvids, suggesting that starlings may be able to distinguish avian predators from other visually similar species.However, this link isn't as simple as it sounds. With these data it is difficult to tease apart cause and effect; so, do large murmurations congregate because predators are close by, or are the predators in fact simply attracted to a bigger group of birds? Despite this, the power of citizen science has, for the first time, enabled a large enough dataset to be assembled for a robust analysis of starling murmuration behaviour to be undertaken.Citizen science is a powerful and growing tool for researchers to draw upon. Although it is not without limitations – such as potential recording errors from untrained participants – it is an extremely effective way of generating large datasets from which to test or generate hypotheses, as well as increasing public interest and involvement in science. Just like the starlings, when many individuals come together to work towards a common goal, great things can be achieved.

¿Es la araña paraphidippus cf. Aurantius (ARANEAE: SALTICIDAE) depredadora o carroñera del colibrí corona violeta (AMAZILIA VIOLICEPS) (Gould, 1859) (Apodiformes: Trochilidae) en México?

RESUMEN. Aunque la depredación activa sobre una variedad depresas es el comportamiento general descrito de las arañas saltarinas, se han registrado otros comportamientos como el ser carroñeras. Las arañas han sido reportadas como depredadoras de aves. A pesar de que, en algunos casos, no está claro si es un evento de depredación o de carroñería. Este es el primer registro formal en México de la araña Paraphidippus cf. aurantius alimentándose del colibrí corona violeta(Amazilia violiceps).

Predatory birds and ants partition caterpillar prey by body size and diet breadth.

The effects of predator assemblages on herbivores are predicted to depend critically on predator-predator interactions and the extent to which predators partition prey resources. The role of prey heterogeneity in generating such multiple predator effects has received limited attention. Vertebrate and arthropod insectivores constitute two co-dominant predatory taxa in many ecosystems, and the emergent properties of their joint effects on insect herbivores inform theory on multiple predator effects as well as biological control of insect herbivores. Here we use a large-scale factorial manipulation to assess the extent to which birds and ants engage in antagonistic predator-predator interactions and the consequences of heterogeneity in herbivore body size and diet breadth (i.e. the diversity of host plants used) for prey partitioning. We excluded birds and reduced ant density (by 60%) in the canopies of eight northeastern USA deciduous tree species during two consecutive years and measured the community composition and traits of lepidopteran larvae (caterpillars). Birds did not affect ant density, implying limited intraguild predation between these taxa in this system. Birds preyed selectively upon large-bodied caterpillars (reducing mean caterpillar length by 12%) and ants preyed selectively upon small-bodied caterpillars (increasing mean caterpillar length by 6%). Birds and ants also partitioned caterpillar prey by diet breadth. Birds reduced the frequency dietary generalist caterpillars by 24%, while ants had no effect. In contrast, ants reduced the frequency of dietary specialists by 20%, while birds had no effect, but these effects were non-additive; under bird exclusion, ants had no detectable effect, while in the presence of birds, they reduced the frequency of specialists by 40%. As a likely result of prey partitioning by body size and diet breadth, the combined effects of birds and ants on total caterpillar density were additive, with birds and ants reducing caterpillar density by 44% and 20% respectively. These results show evidence for the role of prey heterogeneity in driving functional complementarity among predators and enhanced top-down control. Heterogeneity in herbivore body size and diet breadth, as well as other prey traits, may represent key predictors of the strength of top-down control from predator communities.

Anti-parasite treatment and blood biochemistry in raptor nestlings

We investigated the effects of parasite removal on various blood clinical–chemical variables (BCCVs). BCCVs are indicators of health, reflecting, e.g., homeostasis of liver, kidney function, and bone metabolism. The study was conducted in Norway on chicks of two predatory birds: White-tailed Eagle (Haliaeetus albicilla (L., 1758)) and Northern Goshawk (Accipiter gentilis (L., 1758)). Chicks were treated against both endoparasites (internal parasites) and ectoparasites (external parasites). We treated against ectoparasites by spraying nests with pyrethrins. Within nests, chicks were randomly treated with either an anti-helminthic medication (fenbendazole) or sterile water (controls). Treatment against either ectoparasites or endoparasites led to higher levels of the bone and liver enzyme alkaline phosphatase. Bilirubin levels were lower when treated against ectoparasites, whereas bile acids were higher. Anti-endoparasite treatment led to higher creatinine levels. In Northern Goshawks, treating against endoparasites led to higher urea levels and lower potassium levels. Treatment against ectoparasites increased uric acid and urea levels and reduced bilirubin levels and protein:creatinine ratios. In conclusion, anti-parasite treatments led to changes in several BCCVs, suggesting differences in nutrient absorption and physiological state of chicks that are possibly related to the costs of parasitism, but maybe also to the parasite treatment itself.

Percutaneuous distal osteotomy (PDO) for recurrent hallux valgus

Acanthamoeba is a free-living amoeba which can be isolated from environment and among others well known as an opportunist protozoan parasite causing infections in humans and animals. Eyes are extremely important for the wild birds and losing sight ability due to Acanthamoeba can be dangerous.The studies on Acanthamoeba infection in wild birds is very few in world and Turkey therefore we aimed to screen deceased wild birds found in İzmir and Manisa provinces located in western Turkey using PCR and non-nutrition agar (NNA) plate method.Cornea samples were obtained from 18 deceased wild birds. During the external examination, signs of keratitis were observed in two Eurasian sparrowhawks (Accipiter nisus). All of the corneal samples were analyzed by two PCR methods and NNA plate.According to results, the Acanthamoeba positivity in corneal samples was 16.6% and 5.5% by PCR and plate method, respectively. According to sequencing data, two of isolates belonged to genotype T5 and one was genotype T4.In conclusion, Acanthamoeba infection was detected in wild bird cornea samples with/without keratitis for the first time in the world. The result of this study also show that Acanthamoeba can be a cause of keratitis in wild birds of Turkey and thus these predator birds can be a target of other wild animals due to loss of sight ability. In terms of public health, these results show the importance of wild birds as a source of Acanthamoeba infection in nature.

Robird: A Robotic Bird of Prey

Ever since the start of aviation, birds and airplanes have posed a mutual risk: Birds are killed when struck by aircraft, but, in return, bird strikes cause billions in damage to the aviation industry. Airports employ bird-control methods such as audiovisual deterrents (like scarecrows, lasers, and noise), weapons, and chemicals to relocate, suffocate, or otherwise terminate the birds [2]. While the latter methods work, they are ethically questionable. The problem of audiovisual deterrents is that they quickly lose effectiveness due to habituation. The approach that works consistently is the use of predator birds to scare off the prey birds and permanently relocate them away from runways. However, the predators themselves cannot be precisely controlled and, in turn, also pose a threat to airplanes.

The importance of predator species in the population dynamics of the Brown hares (Lepus europaeus, Pallas 1778) – Literature review

One of the conditions for successful small game management is the good management of predator species. The predator species play an important role in the sustainable utilization of the domestic brown hare populations. A portion of these species are under nature protection and with the rest of the species can be utilizing by the wildlife management professionals. Important prey species of brown hares: perspective are red fox, domestic dog and domestic cat. Based on latest date of the National Game Management Database in hunting bags increasing every year the number of the European badger, the stone marten and the golden jackal. In Hungary the brown hare’s most important predator bird species are common buzzard, marsh-harries and goshawk. The human race is not only as a top predator affects the number of the population of brown hares with the wildlife management but indirectly with traffic, (soil cultivation, mowing, and pest control) as well. The control of predators is absolutely necessary for successful small game management, but without sufficient habitat size and habitat development it is hardly sufficient.

Stage-dependent behavioural changes but early castration induced by the acanthocephalan parasite Polymorphus minutus in its Gammarus pulex intermediate host.

Multidimensionality in parasite-induced phenotypic alterations (PIPA) has been observed in a large number of host-parasite associations, particularly in parasites with complex life cycles. However, it is still unclear whether such a syndrome is due to the successive activation of independent PIPAs, or results from the synchronous disruption of a single mechanism. The aim of the present study was to investigate the onset and progression of two PIPAs (a behavioural alteration: reversion of geotaxis, and castration) occurring in the crustacean amphipod Gammarus pulex infected with the acanthocephalan Polymorphus minutus, at different parasite developmental stages. Modifications of geotaxis in hosts differed according to the parasite developmental stage. Whereas the cystacanth stage induced a negative geotaxis (exposing the gammarid to predation by birds, the definitive hosts), the acanthella stage, not yet infective for the definitive host, induced a stronger positive geotaxis (presumably protecting gammarids from bird predation). In contrast, castration was almost total at the acanthella stage, with no significant variation in the intensity according to parasite maturation. Finally, no significant correlation was found between the intensity of behavioural changes and the intensity of castration. We discuss our results in relation with current views on the evolution of multidimensionality in PIPA.

Diversity and Temporal Variation of Avian Fauna in a Rice Growing Landscape in Kurunegala District, Sri Lanka

Rice fields are man-made semi-aquatic ecosystems maintained for the purpose of paddy cultivation. Five contrastingly different successive culture stages viz, preparatory stage, vegetative stage, ripening stage, harvesting stage and post-harvest stage occur along a single paddy culture cycle. Although it has been recorded that a wide variety of fauna are associated with these culture stages, there is a dearth of information on the temporal variation of avian fauna along these culture stages. Therefore, a study was carried out in a rice growing landscape at Katugampola, a rural village in Kurunegala District, to investigate if there is any temporal variation of avian diversity along the culture stages of a paddy culture cycle there. It was hypothesized that the physical and biological characteristics vary along the successive culture stages, and that each culture stage offers a predictable habitat for a distinct assemblage of birds. The sampling protocol of the study included in situ observation, identification and enumeration of different bird species using the fixed radius point count sampling method, and assessing the physical and biological parameters such as the percentage area covered by paddy plants, height of the paddy plants, number of people, number of off road vehicles, number of cattle, number of dogs, sound level, wind speed and the associated insect fauna at each culture stage using appropriate standard field sampling techniques. The study was commenced in May 2014 and lasted until September 2014. Altogether 1892 bird counts were made during the study period where the birds belonged into 19 different species and to 12 different families. Physical and biological parameters also varied significantly (p<0.05 Oneway ANOVA) along the paddy culture cycle. Distinct bird assemblages characteristic to each culture stage were recorded during the study. For example, large predatory birds such as Cattle Egret, Intermediate Egret and Little Egret became abundant during the preparatory stage while small seed eating birds such as sparrows became abundant during the ripening and mature stages. Further, large seed eating birds such as Green Imperial Pigeon and Rose-ringed Parakeet became abundant both during the vegetative stage and the post-harvest stage. The temporal variation of the above bird assemblages appeared to have a direct relationship with the variation of the biological and physical parameters along the paddy culture cycle at Katugampola rice field. Keywords: Avian diversity, Rice growing landscapes, Paddy culture cycle

First time identification of Acanthamoeba genotypes in the cornea samples of wild birds; Is Acanthamoeba keratitis making the predatory birds a target?

Acanthamoeba is a free-living amoeba which can be isolated from environment and among others well known as an opportunist protozoan parasite causing infections in humans and animals. Eyes are extremely important for the wild birds and losing sight ability due to Acanthamoeba can be dangerous.The studies on Acanthamoeba infection in wild birds is very few in world and Turkey therefore we aimed to screen deceased wild birds found in İzmir and Manisa provinces located in western Turkey using PCR and non-nutrition agar (NNA) plate method.Cornea samples were obtained from 18 deceased wild birds. During the external examination, signs of keratitis were observed in two Eurasian sparrowhawks (Accipiter nisus). All of the corneal samples were analyzed by two PCR methods and NNA plate.According to results, the Acanthamoeba positivity in corneal samples was 16.6% and 5.5% by PCR and plate method, respectively. According to sequencing data, two of isolates belonged to genotype T5 and one was genotype T4.In conclusion, Acanthamoeba infection was detected in wild bird cornea samples with/without keratitis for the first time in the world. The result of this study also show that Acanthamoeba can be a cause of keratitis in wild birds of Turkey and thus these predator birds can be a target of other wild animals due to loss of sight ability. In terms of public health, these results show the importance of wild birds as a source of Acanthamoeba infection in nature.

Abiotic factors and biotic interactions jointly drive spider assemblages in nest-boxes in mixed forests

Although spiders are common inhabitants of tree cavities, factors that drive their community structure in these microhabitats are little known. Here we investigated whether bark type, season, intraguild predation (IGP) among spiders, and presence of vertebrate predators can influence the spider community structure in tree cavities. We examined spider abundance and the taxonomic and functional composition of spiders in nest-boxes within two mixed forest stands in central Slovakia in 2012–2013. In total, 1211 spiders belonging to 31 species were sampled from 60 nest-boxes at two sites over three seasons. Spider abundance peaked in autumn as spiders sought wintering sites. Guilds and taxonomic composition changed seasonally with spring and autumn communities dominated by “Other hunters” (Anyphaenidae, Clubionidae, Philodromidae) while during summer the community was dominated by “Sheet web weavers” (Linyphiidae). The guild and taxonomic turnover may be partly explained by the interaction between spiders' phenology and IGP exerted by winter-active spiders on smaller spiders from autumn until spring. Bark type influenced the guild composition as dominance of “Space web weavers” was higher in trees with rough bark than in trees with smooth bark. The rough bark also reduced the intensity of IGP by Anyphaena accentuata (Sundevall, 1833) on philodromids. The presence of insectivorous birds reduced the abundance of spiders by 67%. The presence of bird predators altered the guild composition as they affected mostly the web spiders. The results show that the biotic interactions and abiotic factors interactively determined the spider community structure in the nest-boxes depending on spiders' functional traits.

Local habitat disturbance increases bird nest predation in the Brazilian Atlantic rainforest

Local habitat disturbance increases bird nest predation in the Brazilian Atlantic rainforest

Predation of Birds by Domestic Cats on a Neotropical Island

Predation of Birds by Domestic Cats on a Neotropical Island

Avian nest abandonment prior to laying—a strategy to minimize predation risk?

Nest abandonment prior to laying is poorly understood and rarely studied. One possible explanation is that it is a behavior which may have evolved in response to high predation risk in nesting birds as a strategy to avoid the even greater costs of losing eggs or chicks. We tested this hypothesis in the Grey Fantail (Rhipidura albiscapa), a species that builds and abandons multiple nests throughout its breeding season without laying eggs. We placed artificial nests (that contained natural and plasticine eggs) in the exact locations of natural nests from the previous breeding season (spanning a large elevational gradient) for which the fate was known (abandoned, predated, or fledged). Trials were conducted early and late in the breeding season to test for temporal patterns. We postulated that should nest abandonment indeed reduce predation risk, then artificial nests placed at previously abandoned nest sites should have a greater risk of predation than nests placed at predated or fledged nest sites. Overall, we found that 74% of artificial nests were predated, with predation attributed to birds (66%), small mammals (7%), ants (8%), and unknown predators (19%). Artificial nest predation varied according to previous nest fate, whereby predation rates were lowest for predated sites, slightly higher for fledged, and highest at previously abandoned nest sites. In addition, cover increased survival rates for all nest site types. However, we observed a shift in the proportion of nests predated by birds versus other predator taxa, whereby nest predation by birds was highest late in the season at high elevation; this increase may have been due to extreme high temperatures at low elevation resulting in bird predators moving to refuges at higher elevation.

Optimal background matching camouflage.

Background matching is the most familiar and widespread camouflage strategy: avoiding detection by having a similar colour and pattern to the background. Optimizing background matching is straightforward in a homogeneous environment, or when the habitat has very distinct sub-types and there is divergent selection leading to polymorphism. However, most backgrounds have continuous variation in colour and texture, so what is the best solution? Not all samples of the background are likely to be equally inconspicuous, and laboratory experiments on birds and humans support this view. Theory suggests that the most probable background sample (in the statistical sense), at the size of the prey, would, on average, be the most cryptic. We present an analysis, based on realistic assumptions about low-level vision, that estimates the distribution of background colours and visual textures, and predicts the best camouflage. We present data from a field experiment that tests and supports our predictions, using artificial moth-like targets under bird predation. Additionally, we present analogous data for humans, under tightly controlled viewing conditions, searching for targets on a computer screen. These data show that, in the absence of predator learning, the best single camouflage pattern for heterogeneous backgrounds is the most probable sample.

Edge, height and visibility effects on nest predation by birds and mammals in the Brazilian cerrado

Edge influence is one of the main impacts in fragmented landscapes; yet, most of studies on edge influence have focused on high-contrast edges, and the impacts of low-contrast edges and narrow linear openings are less understood. Edge influence often affects bird nest predation, but these effects are not ubiquitous and may depend on characteristics such as nest height and visibility. We performed an experiment on nest predation in a migratory passerine, Elaenia chiriquensis (Lesser Elaenia; Passeriformes: Tyrannidae), in a savanna vegetation of the Brazilian Cerrado biome in South-Eastern Brazil. We used 89 real E. chiriquensis nests, collected during previous reproductive seasons, with two plasticine eggs in each, and randomly distributed them at two locations (edge – up to 20 m from a firebreak edge and interior – approx. 150–350 m from the edge) and two heights (low – 60–175 cm and high – 190–315 cm above ground). We also measured leaf and branch density around each nest. We performed this study on two 15-days campaigns, checking the nests every 2–3 days and removing those with predation marks. We sorted the predation marks into those made by birds, mammals, or unidentified predators, and used generalized linear models to assess the effects of location, height and leaf density on survival time and predator type. Only four nests had not been predated during the experiment; 55 nests were predated by birds, 7 by mammals, and 23 by unidentified predators. Low nests in the interior tended to have larger survival times whereas high nests at the edge tended to be more predated by birds and less predated by mammals. Thus, even a low-contrast (firebreak) edge may significantly increase nest predation, which is also affected by the nest's height, mainly due to predation by birds. These effects may be due to predator movement along the edge as well as to edge-related changes in vegetation structure. We suggest that higher-contrast edges which may also be used as movement conduits, for example powerline openings, may have even stronger effects, demanding further studies.

Levels of Organochlorine Pesticides Are Associated with Amyloid Aggregation in Apex Avian Brains.

Organochlorine (OC) pesticides pose a significant environmental risk to wildlife and humans and have been associated with Alzheimer's disease (AD). This study aims to spectroscopically analyze brains from free-flying birds and link the results to OC exposure and consequent amyloid aggregation. As long-lived apex predators, predatory birds represent a sentinel species similar to humans. Therefore, the results have implications for both species and may also add to our understanding of the role OC pesticides play in the development of AD. Brains of wild Sparrowhawks were analyzed using ATR-FTIR and Raman spectroscopy and Congo red staining; results were correlated with OC pesticide concentrations in livers. Effects of OC exposure were sex- and age-dependent and associated alterations were seen in lipids and protein secondary structure. A shift from α-helix to β-sheet conformation of proteins indicated that concentrations of OC pesticides >7.18 μg/g may lead to cerebral amyloid aggregation.

Lack of alarm calls in a gregarious bird: models and videos of predators prompt alarm responses but no alarm calls by zebra finches

Many vertebrates use vocalizations to communicate about the presence of predators, and some encode information about predator type or behavior. A fast-approaching predator typically elicits a “flee alarm call,” prompting others to escape to safety. In a field experiment, we presented gliding models of a predatory bird to several species representing four families of passerine, including our model species, the zebra finch (Taeniopygia guttata). All families presented with the glider gave a distinct call on at least one occasion, apart from the zebra finch, for which no specific alarm call was recorded. Following on from this unexpected result, we conducted an experiment in which we exposed captive zebra finches to video of a looming raptor. Results of the captive study showed that birds responded to the looming raptor with escape behavior and responded to less threatening stimuli with orienting or startle behavior. Despite this anti-predator response, birds did not give any distinct alarm call, and the distance calls of both males and females did not differ in structure or rate of delivery after exposure to a stimulus. Zebra finches are one of the most studied birds in the world, are gregarious, and have a rich vocal repertoire, yet their alarm communication has not been investigated experimentally. Our results are consistent with the hypothesis that zebra finches lack a flee alarm call and appear not to signal about immediate danger through a change in calling rate. Many animals emit alarm calls when faced with a threatening event in order to communicate with nearby group members. Threatening events can be simulated with models or by presenting a video of a looming stimulus on a screen. In separate studies, we presented gliding models and computer animations of a hawk to zebra finches, a bird species used in studies around the world, in order to test if they gave alarm calls to warn others of approaching danger. Although birds fled in response to the simulated predators, they did not emit a distinct alarm call. The birds also did not change their rate of calling or the acoustic structure of their distance calls. Surprisingly for a social and highly vocal species, the birds appear to lack alarm calls warning flockmates of immediate danger.