Carrion Crows Corvus Corone Research Articles

Population change of avian predators and grey squirrels in England: is there evidence for an impact on avian prey populations?

Summary 1. Using novel analytical methods applied to extensive national bird and mammal monitoring data, we examine whether 29 English bird populations may have been depressed by increases in the abundance of two broad categories of predators. The first includes predators of juvenile and adult birds: Eurasian sparrowhawks Accipiter nisus, common kestrels Falco tinnunculus and common buzzards Buteo buteo, and the second comprises five nest predators: carrion crow Corvus corone, black-billed magpie Pica pica ,E urasian jayGarrulus glandarius, great spotted woodpecker Dendrocopos major and grey squirrel Sciurus carolinensis. 2. For 22 avian prey species, there is no evidence that increases in common avian predators and grey squirrels are associated with large-scale depression of prey abundance or population declines. For the remaining seven, some negative correlations are biologically unlikely but we cannot exclude the possibility that some of the negative associations are causally related. For example, a particularly strong negative relationship between sparrowhawk and tree sparrow during the Common Birds Census period (1967–2000) could indicate a causal relationship. In contrast, the negative association between buzzard and goldfinch during the Breeding Bird Survey period (1995–2005) is, on ecological grounds, unlikely to do so. Whilst a correlative study such as this cannot prove causation, it provides a focus for more detailed work on particular species. 3. Unexpected was a large number of positive associations between predators and prey, particularly for native avian nest predators, which largely exonerates these predators as driving declines in passerine numbers. 4. Synthesis and applications. Analyses of large-scale and extensive national monitoring data provides little underlying evidence for large-scale impacts of widespread avian predators and grey squirrels on avian prey populations, although we cannot exclude the possibility that a small number of negative associations between particular predator and prey species reflect causal relationships or that predators affect prey species at smaller spatial scales.

Changes in breeding success and abundance of ground-nesting moorland birds in relation to the experimental deployment of legal predator control

Summary 1. An 8-year-field experiment on moorland in northern England manipulated the abundance of legally controllable predators whilst maintaining consistent habitat conditions. Subsequent changes in both the breeding success and abundance of five ground-nesting bird species were monitored: lapwing Vanellus vanellus, golden plover Pluvialis apricaria, curlew Numenius arquata, red grouse Lagopus lagopus scoticus and meadow pipit Anthus pratensis and the abundance only of snipe Gallinago gallinago and skylark Alauda arvensis. 2. Control of fox Vulpes vulpes, carrion crow Corvus corone, stoat Mustela ermina and weasel Mustela nivalis reduced the abundance of fox (−43%) and crow (−78%); no changes were detected in already low stoat or weasel abundances. 3. Reductions in foxes and crows led to an average threefold increase in breeding success of lapwing, golden plover, curlew, red grouse and meadow pipit. 4. Predator control led to subsequent increases in breeding numbers (≥14% per annum) of lapwing, curlew, golden plover and red grouse, all of which declined in the absence of predator control (≥17% per annum). 5. Synthesis and applications. Controlling predators is a potentially important management tool for conserving a range of threatened species. Considerable sums of public monies are currently spent on habitat improvement for conservation and some of these public funds should be used to underpin habitat works with predator removal.

Use of external biometrics to sex Carrion Crow Corvus corone, Rook C. frugilegus and Western Jackdaw C. monedula in Northern England

Carrion Crow Corvus corone, Rook C. frugilegus and Western Jackdaw C. monedula culled as part of a predator control study in Northern England were sexed by inspecting internal reproductive organs and measured to determine whether external biometrics (wing, head‐plus‐bill and tarsus length) could be used to identify the sex of live birds. Tarsus length was found to vary between observers measuring the same bird so was not considered further. Due to considerable size overlap between the sexes it was not possible to sex all individuals correctly, particularly those less than a year old. The larger males and smaller females could be sexed with 85–93% accuracy, in adult birds using wing length of Carrion Crows of male >327 mm, female <309 mm; Rook male >320mm, female <307 mm; and Western Jackdaw male >246 mm, female <233 mm. Head‐plus‐bill length improved the number of birds sexed when used in combination with wing length for Carrion Crow and Rook.

Identifying predators of eggs and chicks of Lapwing Vanellus vanellus and Black‐tailed Godwit Limosa limosa in the Netherlands and the importance of predation on wader reproductive output

Farmland bird populations in the Netherlands have shown an accelerating decline in recent years, despite extensive conservation efforts including reserves, agri‐environment schemes and protection of nests by volunteers. Although agricultural intensification is the main cause underlying these declines, there is a growing concern that the ongoing decline of grassland‐breeding shorebirds in recent years is caused or aggravated by increasing predation. Although Red Fox Vulpes vulpes and Carrion Crow Corvus corone are often accused of causing widespread breeding losses, and calls for management of these species are made, very few field data are available on the incidence of predation on grassland shorebirds and the relative importance of different predators. To obtain such data, we identified egg predators using temperature loggers and continuous video recordings of 792 clutches, and chick predators by radiotagging 662 chicks of Black‐tailed Godwit Limosa limosa and Northern Lapwing Vanellus vanellus. In total, 22 species were identified as predators of eggs or chicks, of which Red Fox, Common Buzzard Buteo buteo, Grey Heron Ardea cinerea and Stoat Mustela erminea were the most frequent. Eggs were taken primarily by mammals and chicks more often by birds. There was great variation in predation levels and species involved in predation of clutches between sites and years, but less in chick predation. Hence, there was no correlation between predation levels on clutches and those on chicks within the same sites. In sites where more then 50% of clutches were lost to predation, however, nocturnal predators took the larger share. As temporal and spatial variation on a small scale significantly influences predation levels, a site‐specific approach based on sound knowledge of the local situation will be more effective in reducing predation on farmland birds than general, country‐wide measures. Calculations based on our data indicate that eliminating only one loss factor at a time will often not reverse a local population decline, and provide a strong argument for targeting several locally limiting factors simultaneously instead of focusing on mitigation of predation alone.

The direct and indirect effects of predation by Hen Harriers Circus cyaneus on trends in breeding birds on a Scottish grouse moor

Two phases of an experimental reduction in management at Langholm Moor in southwest Scotland provided an insight into factors that determined trends in the abundance of moorland birds. In 1992 the historical control of breeding Hen Harriers Circus cyaneus stopped and in 2000 grouse moor management was discontinued. Golden Plover Pluvialis apricaria, Lapwing Vanellus vanellus, Curlew Numenius arquata and Red Grouse Lagopus lagopus scoticus declined, whilst Carrion Crow Corvus corone and Snipe Gallinago gallinago increased. Hen Harriers increased from two to 20 breeding females, then declined back to two. Lapwing abundance was positively associated with that of Hen Harriers, and moorland passerines (Skylark Alauda arvensis, Meadow Pipit Anthus pratensis and Stonechat Saxicola torquata) were negatively associated. Golden Plover, Lapwing, Curlew, Red Grouse, Skylark and Hen Harrier were more abundant when the moor was managed for grouse, whilst Carrion Crow, a common predator of clutches of ground‐nesting birds, increased during the second half when management ceased. Increased Crow numbers, together with an increase in Red Foxes Vulpes vulpes, probably contributed to the observed bird declines.

Predation of Lapwing Vanellus vanellus nests on lowland wet grassland in England and Wales: effects of nest density, habitat and predator abundance

There is concern that predation of Lapwing Vanellus vanellus nests may create additional pressure on declining populations of this species in Europe. At seven sites in England and Wales, daily nest predation rates on 1,390 nests were related to variables using Generalised Linear Mixed Models. The strongest predictor was Lapwing nest density (number of nests within 100 m): predation rates declined as nest density increased. Since nocturnal species, probably mammals, have been identified as the major predators of Lapwing nests at these sites, these results suggest that Lapwings are able to deter mammalian predators or may settle to nest at high densities in areas with low predation pressure. At the site level, there was no relationship between Lapwing nesting density and fox density, and a positive relationship with Carrion Crow Corvus corone nesting density. There was a weaker effect of distance to field boundary: nests closer to boundaries were more likely to be predated. Weak interactive effects between crow density and both nest visibility and distance to vantage point were identified in models using a reduced subset of nests. These were counter-intuitive, did not persist in the larger data set, and do not have obvious explanations. If Lapwings nesting at high density are able to deter predators, there are implications for land management. Smaller areas could be managed within potential breeding habitat to encourage Lapwings to nest in dense colonies. Selection of larger fields for such management, where nests could be located far from the field boundary should improve the value of such measures.

Hybrid zone maintenance by non-adaptive mate choice

In a spatial simulation we show that formation of a stable, narrow hybrid zone requires no selection, only that individuals can recognize their own population type since this is a prerequisite for assortative mating. The European crow occurs in two species/subspecies that meet in a long hybrid zone, the black carrion crow Corvus corone and the grey and black hooded crow C. cornix. In a previous study (Brodin A, Haas F (2006) Anim Behav 72:139) we mimicked sexual imprinting in nestling crows with artificial neural networks, using a learning process that simulates proximate retina perception. The networks were trained on 700 images to recognize either carrion, hooded or hybrid phenotypes as their own. After training the networks were exposed to 300 new, unfamiliar pictures of crows. The networks that had been trained on pure subspecies then showed strong preference for their own type. Networks trained on hybrid crows showed weaker preference for their own type. Assuming that these preferences will determine mate choice preferences we have combined them with empirical data on dispersal of young crows to investigate what kind of geographical distribution pattern this would create. We then assume that the two subspecies meet and hybridize along a straight border. In only 60 generations a stable, narrow hybrid zone that resembles the real hybrid zone was formed. This zone remained stable over time. With minor adjustments of parameters the results would not only fit the width but also the shapes of the clines in the field.

The impact of predator control on lapwing Vanellus vanellus breeding success on wet grassland nature reserves

Summary Whilst the widespread declines in breeding grassland waders in many parts of Europe have been associated with changes in agriculture, there is concern that predation may compromise recovery of wader populations, even in situations where habitat is suitable, such as nature reserves managed for breeding waders. An 8‐year cross‐over experiment was used to examine the effect of red fox Vulpes vulpes and carrion crow Corvus corone control on breeding performance and population trends of lapwing Vanellus vanellus on 11 lowland wet grasslands. Predator densities in the absence of control measures were highly variable among sites, and consequently the numbers of predators removed were similarly variable. Overall, predator control measures resulted in a 40% decline in adult fox numbers and a 56% reduction in territorial crows. There was no overall effect of predator control on the failure rate of 3139 lapwing nests. However, the effect of predator control varied significantly among sites, reflecting the variation in predator densities. Predator control measures were more likely to result in increased nest survival at sites where predator densities were high. Nest‐temperature loggers deployed at seven sites indicated that 88% of nest predations occurred during darkness, suggesting nocturnal mammalian predators. At seven sites predator control had no overall effect on chick survival, monitored by radio‐tracking 459 chicks, but there were differences in the effect of predator control among sites. Densities of predators were low during years without predator control measures at the majority of these sites. At six further sites breeding success, assessed from the proportion of adults accompanied by young late in the season, was twice as high in years when predators were controlled. There was no overall effect of predator control on lapwing population trends across the experimental sites. Synthesis and applications. This study highlights the need for information on predator densities and the impact of predators on nest and chick survival, before embarking on predator control measures at a particular site. A decision tree for determining the circumstances in which fox and/or crow control may be both necessary and effective is recommended.

What effects do walkers and dogs have on the distribution and productivity of breeding European Nightjar Caprimulgus europaeus?

Several successive studies of European Nightjars Caprimulgus europaeus (hereafter, Nightjar) on the Dorset heaths demonstrated negative effects of the proximity of urban development and associated disturbance from access on foot by people and dogs. Surrogate measures of human density and settlement, including the amount of developed land around each heathland patch and the number of houses, were significantly and negatively related to the density of Nightjars (using data from the 1992 national survey) on heathland patches, regardless of patch size. These findings prompted targeted field studies, the subject of this paper, which investigated the mechanisms and effects of recreational disturbance on breeding Nightjars. Fieldwork in 2002 focused on a suite of heathland sites representing a range of access from sites closed to the public to heaths heavily used for recreation, notably by dog walkers. Studies in 2003 concentrated on the heavily used heaths. Nests which failed were significantly closer to paths, tended to be closer to the main points of access to heaths, in areas with higher footpath density, notably of high levels of use, and in more sparsely vegetated locations. The proximate cause of nest failure was most frequently egg predation. Nest cameras, deployed in 2003 in an attempt to identify the predators of eggs or chicks, recorded just one instance of predation, that of an egg by a Carrion Crow Corvus corone, and two instances of the incubating bird being flushed by a dog, once from an egg and once from a chick, neither event preventing fledging. Flushing rate of Nightjars from the nest was associated with the height of vegetation around the nest and the extent of nest cover. The studies indicate that access disturbance interacts with environmental conditions for breeding birds. Birds flush more readily from eggs, which are highly visible when exposed, especially in areas with sparse nest cover, leaving them vulnerable to predation. Although Nightjar flushing rates were observed to be low in 2003, just one event leading to predation is enough to end that nesting attempt. Management measures are recommended to minimize the effects of walkers and their dogs on Nightjars.

Failure of Methiocarb to Produce Conditioned Taste Aversion in Carrion Crows Consuming Little Tern Eggs

Abstract An experimental procedure was set up to test if Carrion Crow (Corvus corone) predation on Little Tern (Sterna albifrons) eggs could be decreased by conditioned taste aversion. The experiment started with a control period, during which 30 artificial Little Tern nests were maintained with quail eggs for 6 days at two study sites. The rate of egg predation was assessed through daily visits and observations of crow behavior. During the treatment period (following 6 days), 15 nests were supplied with eggs pre-treated with methiocarb, an ill-inducing compound, while the other 15 nests were maintained with non-treated eggs. The treatment period was extended by a further period of eight days, during which only treated eggs were deployed at 15 nests. Carrion Crows did not develop any aversive response to the eggs. All treated and untreated eggs were taken by crows from the nests and broken in less than 24 h after delivery. However, treated eggs were apparently not consumed by crows, which suggests that th...

ハシボソガラスとハシブトガラスの営巣密度推定のための予測モデル構築

Nesting locations of two species of crows, the Carrion crow Corvus corone and the Jungle crow C. macrorhynchos, were studied in five areas of total 58km2 near Tsukuba city in southern Ibaraki prefecture, about 50km northeast of Tokyo. Using these data, multiple regression models were constructed to predict the breeding density (number of nesting locations within a 1x1km or 2x2km grid) of the crows from environmental factors such as vegetation, land use and terrain structure. Overall, 2x2km grid models were better than 1x1 models and the one to predict the breeding density of the two crow species combined was better than separate models. The factors used in this combined model were the total length of the forest edge facing farmland, paddy field, orchard, grassland and urban area and the area of farmland (R2=0.83). The presence of these edges might indicate the abundance and the proximity of foraging and nesting habitat for the crows. The model to predict the ratio of the two species was also constructed (R2=0.77). Its structure suggested that forested areas tended to have more Jungle than Carrion crow nests.

Use of time-lapse video cameras to determine causes of nest failure of Slavonian Grebes Podiceps auritus

Capsule Few clutches were predated, with Otter Lutra lutra the most frequent predator filmed. Aims To determine the rate of nest predation and identify predators of the Slavonian Grebe Podiceps auritus in Scotland. Methods Miniature 24-hour time-lapse video cameras were placed next to 23 Slavonian Grebe nests on five lakes to record nest failure events and to identify predators that depredated the contents of nests. For comparison, ten nests without cameras were also monitored and their outcomes recorded. Results The probabilities of clutch failure due to predation, and wave damage or water level rise were 19% and 30%, respectively. Otters took two clutches and an adult grebe plus chicks from nests. Other predators filmed at nests were Stoat Mustela erminea, Carrion Crow Corvus corone, Common Gull Larus canus and Coot Fulica atra. No difference in predation rates between nests with and without cameras was detected. Otters were recorded at eight of 13 lakes studied. An American Mink Mustela vison was recorded at one lake. Conclusion The nest predation rate of Slavonian Grebe in Scotland was not high compared with other studies and is not of conservation concern.

Effect of parentage and relatedness on the individual contribution to cooperative chick care in carrion crows Corvus corone corone

Carrion crows Corvus corone corone in northern Spain form complex cooperative groups that contain non-dispersing offspring and immigrants. Reproduction is often shared among group members, with polyandry prevalent over joint egg laying. However, due to incest avoidance or sexual immaturity, reproduction is potentially available only to a fraction of group members (“potential breeders”), while others do not breed (“non-breeders”). We combined molecular data with video-recorded observations at nests in order to investigate whether potential breeders and non-breeders adjust their individual effort in nestling feeding respectively to their level of parentage and the relatedness with the chicks. Overall, parents of at least one chick in the brood showed the highest feeding rates. Among potential breeders, genetic mothers and fathers fed chicks at significantly higher rates than individuals with no parentage, but they did not adjust their effort according to the proportion of offspring generated. Current direct fitness benefits are therefore important in determining a high provisioning effort, but crows may lack a mechanism to finely assess their share of parentage. Among non-breeders, males contributed more than females to chick feeding, but we found no significant correlation between feeding rate and relatedness to the nestling. We discuss how the latter result can be reconciled with the fact that kin selection has been shown to be important in shaping the crow cooperative society.

Use and Validation of a Molt Score Index Corrected for Primary-Feather Mass

Abstract In European Starlings (Sturnus vulgaris), mass of new primary feathers increases linearly with time for most of the duration of molt (Dawson 2003). Here, we had two aims: (1) to confirm that mass of new primary feathers increases linearly in other species, and (2) to use that linear increase as the basis of a system to score the progress of molt. Increase in length of primary feathers during molt was recorded for captive Eurasian Magpies (Pica pica), Carrion Crows (Corvus corone), European Greenfinches (Carduelis chloris), and Eurasian Bullfinches (Pyrrhula pyrrhula). Wing shape differs among those species. Feather lengths during molt were converted into mass by using information on final feather length and mass and the distribution of mass from tip to base of feather. Rate of increase in total mass of new primary feathers was largely linear in all four species. A molt scoring method is described in which individual feather scores are weighted to account for the contribution of each particular primary feather's mass toward total primary-feather mass. When the method was tested on eight captive starlings, the increase in mass-corrected molt score was almost linear, unlike the increase shown by the standard scoring system, which exaggerated molt rate during the early part of molt and underestimated it later. In the four species studied here, mass-corrected molt score likewise closely tracked the actual increase in mass, unlike the standard molt score. Because it is based on feather mass, the method presented here is of greater physiological and energetic relevance than the standard method. Because the mass-corrected score increases more linearly with time, it has the additional advantage of enabling less complicated, and potentially more accurate, estimations of molt start dates and molt durations.

Evidence for declines in populations of grassland-associated birds in marginal upland areas of Britain

Capsule We report large declines among summer populations between 1968–80 and 2000. Aim To assess changes in the status of breeding populations of birds in pastoral uplands. Methods Volunteer observers revisited 13 areas of marginal upland in Britain where Common Birds Census data were collected during 1968–80. This allowed the status of 35 bird species to be examined over about 20 years and to make a comparison between grassland-based and woodland-based species. Results For 12 species the decline in abundance was significant, particularly among passerines, such as Skylark Alauda arvensis, Wheatear Oenanthe oenanthe, Whinchat Saxicola rubetra, Yellow Wagtail Motacilla flava and Yellowhammer Emberiza citrinella, each of which declined by over 80%. Redshank Tringa totanus, Yellow Wagtail, Dipper Cinclus cinclus, Whinchat, Wheatear, Ring Ouzel Turdus torquatus and Yellowhammer were found on less than half the number of plots on which they were originally recorded. Most declining species were associated with grassland for nesting and foraging, compared to those species that increased (Wood Pigeon Columba palumbus, Pied Wagtail Motacilla alba, Carrion Crow Corvus corone, Jackdaw C. monedula and Goldfinch Carduelis carduelis) that were less specialized in their habitat requirements. Woodland or woodland edge species showed no significant change in status, suggesting that population declines among grassland species were not due to lower observer effort between recording periods. Conclusion Long-term changes to grassland ecosystems in marginal upland areas of Britain may have influenced the status of bird populations.

Capercaillie breeding success in relation to forest habitat and predator abundance

Summary The capercaillie Tetrao urogallus is widely valued as a game bird and an indicator of forest ecosystem quality. In Scotland, its numbers have declined since the 1970s, due primarily to poor breeding success. We investigated whether differences in breeding success among forests are related to predator abundance or to aspects of forest structure, with a view to identifying beneficial management practices. Capercaillie breeding success was estimated in 7–14 forest areas in Scotland each year during 1991–2001. Forest habitat, including ground vegetation, and indices of predator abundance were assessed in each of the 14 areas in 1995. Capercaillie breeding success increased with increasing bilberry Vaccinium myrtillus ground cover, but did not improve further above 15–20% cover. The main predators were carrion crow Corvus corone, fox Vulpes vulpes and raptors. Indices of their abundance were confounded such that their respective effects on capercaillie breeding success could not readily be distinguished. However, capercaillie breeding success was negatively related to a principal component score that represented the combined abundance of crows, foxes and, to a lesser extent, raptors. A management trial in one forest showed that capercaillie bred better when most crows and some foxes were killed than when they were not. An index of pine marten abundance was related neither to the other predator indices nor to capercaillie breeding success. Synthesis and applications. Capercaillie reared more young in forests with more bilberry and fewer predators. Management to improve the breeding success of capercaillie should aim for at least 15–20% bilberry ground cover, and legal control of crows and foxes.

Are Carrion Crows that congregate in spring roosts juveniles or adults?

Carrion Crows Corvus corone often establish spring roosts even during the breeding season. To examine whether the individuals roosting in spring are juveniles with immature reproductive organs, we compared the body size, sexual organs, and plumage of 150 roosting and 35 breeding individuals collected in the Joetsu region, Niigata, Japan, between 20 April and 9 May 1992. In both sexes, roosting individuals had significantly lighter bodies, and shorter wings and tails than breeding individuals. Roosting males had significantly lighter and shorter testes, and a lower testes/body percentage than breeding males. All 15 breeding males and 17 of 70 roosting males (24.3%) had mature testes, while 53 of 70 roosting males (75.7%) had immature testes. Roosting females had significantly lighter ovaries and a lower ovary/body percentage than breeding females. All 20 breeding females and 19 of 80 roosting females (23.8%) had long, enlarged oviducts, while 61 roosting females (76.2%) had undeveloped oviducts. Based on plumage characteristics, we estimated that 112 of the 150 roosting crows (74.7%) were juveniles. The reproductive organs of 108 of the 112 juveniles (96.4%) and 6 of 38 adults (15.8%) were immature. These results suggest that the spring roost consisted mainly of juveniles with immature reproductive organs. Thirty-six roosting individuals had mature reproductive organs. We considered them to be either territorial adults that had attempted to breed near the roost but failed, or sexually mature non-territorial males.

USE AND VALIDATION OF A MOLT SCORE INDEX CORRECTED FOR PRIMARY-FEATHER MASS

Abstract In European Starlings (Sturnus vulgaris), mass of new primary feathers increases linearly with time for most of the duration of molt (Dawson 2003). Here, we had two aims: (1) to confirm that mass of new primary feathers increases linearly in other species, and (2) to use that linear increase as the basis of a system to score the progress of molt. Increase in length of primary feathers during molt was recorded for captive Eurasian Magpies (Pica pica), Carrion Crows (Corvus corone), European Greenfinches (Carduelis chloris), and Eurasian Bullfinches (Pyrrhula pyrrhula). Wing shape differs among those species. Feather lengths during molt were converted into mass by using information on final feather length and mass and the distribution of mass from tip to base of feather. Rate of increase in total mass of new primary feathers was largely linear in all four species. A molt scoring method is described in which individual feather scores are weighted to account for the contribution of each particular pr...

Tourism, mountain huts and distribution of corvids in the Bavarian Alps, Germany

Anthropogenic resources related to recreational activities and tourism infrastructure may greatly affect wildlife species in the Alps. In this paper, we explore the effects of mountain tourism in the Bavarian Alps, Germany, on the spatio‐temporal distribution of corvids in the post‐fledging period in summer and autumn. We contrast corvid point‐counts in the surroundings of 28 popular mountain huts (hut areas) with those in 22 similar areas rarely visited by humans (control areas). Carrion crows Corvus corone and magpies Pica pica were exclusively observed at huts, and jays Garrulus glarularius occurred in more hut areas than in controls. Alpine choughs Pyrrhocorax graculus, jays and nutcrackers Nucifraga caryocatactes were more numerous at huts than in control areas. Ravens Corvus corax were equally common, but like Alpine choughs, they spent more time foraging in hut than in control areas. Multivariate analyses confirmed that corvid incidence was significantly related to tourist use. However, corvids visited huts regardless of the actual numbers of humans present. Our results suggest that corvids opportunistically adjust their range use to the availability of resources offered by tourism. Mountain huts and other places frequented by humans may thus contribute to an increased carrying capacity for corvids at higher elevations. This may have major ramifications for other species that corvids prey upon or compete with. Mountain tourism in the Alps may thus conflict with conservation efforts for threatened species such as grouse (Tetraonidae).

ハシボソガラスＣｏｒｖｕｓ ｃｏｒｏｎｅのなわばり非所有個体の採食地とねぐらの利用

ハシボソガラスＣｏｒｖｕｓ ｃｏｒｏｎｅのなわばり非所有個体の採食地とねぐらの利用