Northern Goshawk Accipiter Gentilis Research Articles

Using a drone to monitoring arboreal nests of birds of prey

ABSTRACT The breeding parameters of birds are the key element of bird population monitoring. The assessment of nesting success is difficult in the case of arboreal nests, which are typical for birds of prey. Drones are valuable tools for monitoring arboreal nest occupancy. We tested the feasibility of safely monitoring the common buzzard Buteo buteo and northern goshawk Accipiter gentilis nests via drones. We compared assessments of nest occupancy and the number of fledglings in occupied nests using drones with those obtained from traditional ground-based observations. Additionally, the response of the raptors to drone appearance was documented. The assessments of the nest occupancy of the common buzzard from the ground level and the drone were not significantly different. The monitoring of nest occupation by drones was more precise for northern goshawks. Monitoring using drones showed a higher number of juveniles. Adult birds reacted weakly to the presence of the drone. Our study indicates that monitoring arboreal nests of birds of prey with drones is more effective than monitoring arboreal nests from the ground and does not elicit adverse reactions from the birds. Further studies should be conducted to determine the responses of other raptors.

Topography of Retinal Ganglion Cells of a Northern Goshawk Accipiter gentilis

Topography of Retinal Ganglion Cells of a Northern Goshawk Accipiter gentilis

Function of juvenile plumage in the northern goshawk (Accipiter gentilis): aggressive mimicry hypothesis

Multiple raptors show juvenile plumage that is substantially different from that of their parents. Here, we test the prediction that the colouration of the juvenile northern goshawk Accipiter gentilis resembling the colouration of the common buzzard Buteo buteo acts as a form of aggressive mimicry. The goshawk specialises in hunting larger birds and mammals up to the size of geese or hares, while the buzzard preys mostly on small rodents. Larger birds may thus consider juvenile goshawks as less dangerous raptors, and the juvenile goshawk may thus gain an advantage when hunting. We used the Eurasian magpie Pica pica, a common prey of the goshawk, to test this prediction. We compared the behavioural responses of magpie parents defending their freshly fledged young towards mounts of an adult goshawk, juvenile goshawk, and buzzard. To be able to assess whether this behaviour differs from responses to a nest predator and a harmless bird we also presented a common raven Corvus corax and common pheasant Phasianus colchicus as baseline stimuli. Both juvenile and adult goshawks elicited antipredatory behaviour, but magpies took more risks facing juvenile goshawks. Additionally, the intensity of antipredatory behaviour towards the juvenile goshawk was also higher than towards the buzzard. We thus conclude that magpies do distinguish between juvenile and adult goshawks, as well as they do distinguish juvenile goshawks from buzzards. They are able to assess the threat particular raptors represent and respond accordingly. Analysis of spectral reflectance of stuffed specimens of these three raptors suggests there are differences, which can be used for the appropriate recognition. In conclusion, we cannot confirm the hypothesis of aggressive mimicry in juvenile goshawks that interact with magpies.

A long-term study of size variation in Northern Goshawk Accipiter gentilis across Scandinavia, with a focus on Norway.

Changing climate and growing human impacts are resulting in globally rising temperatures and the widespread loss of habitats. How species will adapt to these changes is not well understood. The Northern Goshawk (Accipiter gentilis) can be found across the Holarctic but is coming under more intense pressure in many places. Studies of recent populations in Finland and Denmark have shown a marked decline in body size of Northern Goshawks over the past century. Here we investigate long-term changes to Norwegian populations of Northern Goshawk by including material from the Middle Ages. We measured 240 skeletons of modern Northern Goshawks from Norway, Sweden, Denmark and Finland, and 89 Medieval Goshawk bones. Our results show that Norwegian and Swedish female Goshawks have decreased in size over the past century, whilst males showed little decline. Medieval female Goshawks were larger than contemporary females. A decline in forest habitats and a concomitant shift towards smaller prey likely drove a shift to smaller body size in Northern Goshawks. Our study shows that significant body size changes in birds can occur over relatively short time spans in response to environmental factors, and that these effects can sometimes differ between sexes.

Assessing the influence of raptors on grape-eating birds in a Mediterranean vineyard

Several bird species may cause serious damage to grape production. The ability of raptors as biological control agents of grape-eating birds is poorly understood and under-used. We installed artificial nests and perches to encourage the presence and activity of raptors in vineyards located in central Spain and explored their effectiveness to reduce damage to grapes. We characterized the raptor community by field surveys and assessment of natural breeding sites, evaluated the abundance of grape-eating birds, and sampled damage to grape production for three consecutive years. Raptor community in the study area was diverse (13 species). Breeding of ornitophagous species such as Booted eagle Hieraaetus pennatus and Northern goshawk Accipiter gentilis was confirmed in the forest patches. We identified 10 grape-eating bird species, with Spotless starling (Sturnus unicolor) being the most abundant. Distance from the edges between vineyards and natural and semi-natural woody vegetation affected damage to grapes, with more damage close to the edges. The installed elements did not significantly reduce damage to grapes. Woody vegetation in and around the vineyards may reduce the success of the installed elements by providing shelter to grape-eating birds and suitable sites for raptor breeding and perching. Other variables such as vine orientation, land-cover, and distance to raptor nests did not affect damage to grapes. To promote the conservation of raptors and their regulating services in this Mediterranean agroforestry system, more research is needed to find methods to increase the presence of raptors in vineyards and to manage the woody shelters used by grape-eating birds around crops.

Long-term consistency in susceptibility of prey species to predation by an avian predator

Selection by predators affects prey through competition for limiting resources. This not only has consequences for direct mortality but also indirectly affects disturbance. Changes in the intensity of selection on prey by predators may affect the size of prey populations, with consequences for their short- or long-term interactions. We assessed whether predation by northern goshawks Accipiter gentilis modified the composition of prey communities consistently along a temporal gradient, showing long-term consistency in susceptibility of prey species to predation. We followed six populations of the goshawk in two biomes in Denmark and Finland during 1949-2019. Susceptibility to goshawk predation in 2005-2017 in Denmark was only weakly related to susceptibility to goshawk predation in 1977-2004. In Finland, susceptibility of shared prey species to goshawk predation was positively related between periods. The average difference in susceptibility to goshawk predation between periods was considerably higher in Denmark than in Finland. Susceptibility of prey species to predation in goshawks increased with latitude and body mass of prey species, and decreased with period of time and population density of prey species. The changes in susceptibility to predation suggest changes in the characteristics of the local prey pools.

Anything for a quiet life: shelter from mobbers drives reproductive success in a top‐level avian predator

Understanding how habitat structure relates to reproductive performance of species can help identify what habitats are of the highest quality for a given species and thereby guide effective management. Here, we compared the influence of prey abundance and the amount of shelter area on the relationship between habitat and breeding performance. We focused on the forest‐dwelling northern goshawkAccipiter gentilisin an agroforestry system. Using structural equation modelling, we tested the associations between reproductive performance and three explanatory factors: habitat structure, abundance of food resources or levels of mobbing disturbance, and prey supply to the nest. Our results suggest that habitat structure influences reproductive performance through shelter rather than through prey abundance. During the study period, forested habitats in the breeding territories provided shelter to the goshawk, reducing disturbance by carrion crowsCorvus corone, which acted as large, aggressive, social mobbers. Decreased disturbance increased prey supply to the nest, probably because it favored food accessibility and male goshawk foraging efficiency. Habitat was not significantly associated with quality of the breeders, both in terms of body size and seniority in the territories. Our findings suggest that reproductive performance, and therefore habitat quality, may depend more on sheltered access to food resources than on the amount of food available. Our observation that mobbers decrease predator foraging efficiency highlights the possibility of designing effective, socially acceptable predator management strategies to protect sensitive domestic prey.

The taxonomic status of Palearctic and Nearctic populations of northern goshawk Accipiter gentilis (Aves, Accipitridae): New evidence from vocalisations

The taxonomic status of the North American and Eurasian populations of northern goshawk A. gentilis has been called into question by recent molecular studies, indicating the need for additional taxonomic study. Vocalisations have long played an important role in diagnosing potentially reproductively isolated groups of birds. The chattering-type call of A. gentilis plays a role in advertisement and pair-contact, making this a suitable basis for taxonomic study of vocalisations. The data set consisted of recordings of the calls of 75 individuals of the Eurasian gentilis-group of A. gentilis, 37 of the North American atricapillus-group of A. gentilis and, for comparison, seven of Henst’s goshawk A. henstii. The three groups showed non-overlapping variation in the duration of call-notes and also showed several other highly significant differences. Discriminant Function Analysis resulted in 100% correct classification of recordings into the three groups. It is here argued that the new bioacoustic data, in combination with previous evidence of morphological, mitochondrial DNA and genomic DNA differences between Eurasian and North American A. gentilis, suggests that two species are best recognised: northern goshawk A. gentilis and American goshawk A. atricapillus. A. gentilis / A. atricapillus add to a growing list of Holarctic temperate zone taxa that have recently been recognised as separate species based on a deep phylogeographic split between Eurasian and North American populations in combination with differences in other characters. This is the first quantitative taxonomic study of vocalisations in Accipitridae.

Feathers as an integrated measure of organohalogen contamination, its dietary sources and corticosterone in nestlings of a terrestrial bird of prey, the northern Goshawk (Accipiter gentilis)

In this study, we evaluated the suitability of body feathers, preen oil and plasma for estimation of organohalogen compound (OHC) exposure in northern goshawk Accipiter gentilis nestlings (n = 37; 14 nests). In addition, body feathers received further examination concerning their potential to provide an integrated assessment of (1) OHC exposure, (2) its dietary sources (carbon sources and trophic position) and (3) adrenal gland response (corticosterone). While tetrabromobisphenol A was not detected in any sample, the presence of polychlorinated biphenyls, organochlorine pesticides, polybrominated diphenyl ethers and hexabromocyclododecane in body feathers (median: 23, 19, 1.6 and 3.5 ng g−1 respectively), plasma (median: 7.5, 6.2, 0.50 and 1.0 ng g−1 ww, respectively) and preen oil (median: 750, 600, 18 and 9.57 ng g−1 ww, respectively) suggests analytical suitability for biomonitoring of major OHCs in the three matrices. Furthermore, strong and significant associations (0.20 ≤ R2 ≤ 0.98; all P < 0.05) among the OHC concentrations in all three tissues showed that body feathers and preen oil reliably reflect circulating plasma OHC levels. Of the dietary proxies, δ13C (carbon source) was the most suitable predictor for variation in feather OHCs concentrations, while no significant relationships between body feather OHCs and δ15N (trophic position) were found. Finally, body feather corticosterone concentrations were not related to variation in OHC concentrations. This is the first study to evaluate feathers of a terrestrial bird of prey as an integrated non-destructive tool to jointly assess nestling ecophysiology and ecotoxicology.

How much to carry? Implications of maximum load carrying capacity for prey use of urban and rural Northern Goshawks Accipiter gentilis

ABSTRACT Capsule: Compared to their rural counterparts, urban Northern Goshawks Accipiter gentilis potentially maximize their energy delivery to the nest by exploiting heavier prey species close to their maximum carrying capacity. Aims: We aimed to assess prey use of a raptor species with distinct reversed sexual size dimorphism from a perspective of physical limitations during foraging and the transportation of prey. Methods: We estimated the theoretical maximum load carrying capacity (MLCC) of fully developed Northern Goshawks based on their flight muscle mass. Additionally, we collected data on the breeding season diet of Northern Goshawks in urban and rural habitats in Germany. By linking MLCC estimates to the diet we explained the relevance of prey size from a viewpoint of load carrying capacity. Results: Estimates for the mean (± sd) additional portable loads were 684 g (± 237) for males and 971 g (± 235) for females, accounting for 96% and 84% of their body mass, respectively. Overall prey weight averaged higher for urban areas compared to rural ones, while the majority of prey items were between 200 and 500 g and below the estimated MLCC of both sexes, with the exception of single heavy species. Results suggest that prey use of Northern Goshawks during the breeding season is barely limited by prey transportability, since both sexes are physically capable of carrying the majority of prey species to their nest. Conclusions: Urban Northern Goshawks can exploit heavier, available prey species compared to their rural counterparts, allowing them to hunt larger prey closer to their MLCC. Ultimately, by maximizing their energy delivery to the nest, this presumably constitutes one key factor why Goshawks successfully colonized European cities. This study is the first to link estimates of physical limitations in prey transportation for a free-living raptor species to its prey composition in the light of colonizing urban environments.

To get sick or not to get sick\u2014Trichomonas infections in two Accipiter species from Germany

Trichomonosis caused by the flagellate Trichomonas gallinae is one of the most important avian diseases worldwide. The parasite is localised in the oesophageal area of its host and mainly infects pigeon and dove species. During the last decade, a host expansion to passerine birds occurred, making the disease a potential threat for passerine predators as naïve host species. Here, we investigated the effect of the parasite on two Accipiter species in Germany which show a comparable lifestyle but differ in prey choice, the Northern goshawk (Accipiter gentilis) mainly hunting pigeons and the Eurasian sparrowhawk (Accipiter nisus) mainly feeding on passerines. We genetically identified the parasite strains using the Fe-Hydrogenase gene as marker locus and compared the incidence of parasite presence and clinical signs of trichomonosis between nestlings of the two Accipiter species. In total, we identified 14 strains, with nine strains unknown so far. There was a higher strain diversity and prevalence of Trichomonas spp. in goshawks than sparrowhawks (42.4% vs. 21.2%) whereas sparrowhawks when being infected more often displayed clinical signs of trichomonosis than goshawks (37.1% vs. 6.1%). Even though sparrowhawks were mainly infected with the finch epidemic strain and genetic data indicated some variation between isolates, no correlation with virulence could be detected. All in all, goshawks seem to be better adapted to Trichomonas infections, whereas to sparrowhawks, this is a novel disease with more severe manifestations, from individual morbidity to a higher risk of population decline caused by trichomonosis.

The Ghost of the Hawk: Top Predator Shaping Bird Communities in Space and Time

Despite the wide recognition that strongly interacting species can influence distributions of other species, species interactions are often disregarded when assessing or projecting biodiversity distributions. In particular, it remains largely uncharted the extent to which the disappearance of a keystone species cast repercussions in the species composition of future communities. We tested whether an avian top predator can exert both positive and negative effects on spatial distribution of other species, and if these effects persist even after the predator disappeared. We acquired bird count data at different distances from occupied and non-occupied nests of Northern goshawks Accipiter gentilis. Using a Bayesian joint species distribution model, we found that large bird species (preferred prey) are less abundant in the proximity of nests occupied by goshawks, whereas smaller species –expected to get protection from subordinate predators displaced by goshawks– more often showed an opposite association. These spatial differences level off gradually, but still persist for years after the goshawks have disappeared. This indicates that the composition of local bird populations and communities might be conditional on past species interactions. Therefore, endeavors centered around species distributions could largely benefit from acknowledging the local extinction of keystone species.

The co-occurrence of Ural Owls Strix uralensis and Northern Goshawks Accipiter gentilis differs between extensive and fragmented forests

ABSTRACT Capsule Territories of the nocturnal Ural Owl Strix uralensis and diurnal Northern Goshawk Accipiter gentilis were spatially associated in fragmented forest but not in extensive forest. Aims To test the hypotheses that (i) the patterns of distribution of Ural Owl and Northern Goshawk territories are different in extensive and fragmented forests and (ii) the distribution of their territories do not depend on local forest structure and habitat variables. Methods The territories of Northern Goshawks and Ural Owls were identified in forests in southern Poland. Spatial analysis was used to examine the co-occurrence patterns of the two species, and multivariate analysis to examine the impact of environmental cues on territory selection. Results Most habitat parameters were not significantly related to the presence of territories of either species. For Northern Goshawk there was a positive association with the occurrence of old-growth patches and a negative association with clear-cut areas and proximity to forest edge in fragmented forests; for Ural Owl there was a significant effect of wood type in extensive forest. None of the habitat parameters distinguished the territories of the two species, suggesting similarity in the habitats used. The territories of the two species were spatially associated in fragmented forests, suggesting some positive interspecific relationship. In contrast, the distributions of the two species were not significantly associated in extensive forest. Conclusions To explain the spatial co-occurrence between Northern Goshawks and Ural Owls we suggest: (i) Ural Owls can occupy unused Northern Goshawk nests in managed extensive forest where there is a deficiency of large tree cavities; (ii) restricted availability of habitat in fragmented forests forces both species to nest in close proximity, and/or (iii) Ural Owls use social information from Northern Goshawks about habitat quality when selecting territories in some landscapes.

The taphonomy of medium‐sized grouse in food remains of the northern goshawk Accipiter gentilis, compared with damage done by man and other predators

AbstractThis study describes bone damage of medium‐sized grouse (Lyrurus tetrix and Lagopus spp.) in food remains of the northern goshawk Accipiter gentilis and compares it to damage done by other birds of prey and humans. In general, the ‘signature’ left on the bones by the goshawk is similar to those of other diurnal birds of prey, but it differs from human‐derived damage and from owl pellets. These differences are visible in bone preservation, fragmentation and perforation. This study is the first to describe the characteristic damage to the sternum and coracoid that is probably typical of other raptors as well. Reliable analysis of zooarchaeological materials requires not only correct identification to the species but also determining where the bones came from at a given site. Bird bones from open‐air archaeological sites may contain food remains of the goshawk, whose habitat is forests in the vicinity of open areas. This study will assist in determining the factor(s) responsible for the accumulation of zooarchaeological materials.

Killing of raptors on grouse moors: evidence and effects

Owing to the intensity of game management in Britain, managers of grouse moors have illegally killed raptors to increase the numbers of Red GrouseLagopus l. scoticaavailable for shooting. This paper summarizes evidence for the recent scale of illegal raptor killing on grouse moors and its effects on populations. It provides insights into how raptors themselves respond demographically to different levels of killing. Over Britain as a whole, most raptors have increased and expanded considerably since the 1970s, in response to reduced killing and nest destruction, and the diminished impacts of organo‐chlorine pesticides; however, in recent decades the populations of some species have declined on and around grouse moors. This is widely evident in Hen HarrierCircus cyaneus, Peregrine FalconFalco peregrinusand Golden EagleAquila chrysaetospopulations and in more restricted areas also in Northern GoshawkAccipiter gentilisand Red KiteMilvus milvuspopulations, in all of which illegal killing has been sufficient to affect numbers over wider areas. The evidence consists mainly of: (1) greater disappearance of nesting pairs, lower breeding densities or reduced occupancy of apparently suitable traditional territories on grouse moors compared with other areas; (2) reduced nest success compared with other areas; (3) reduced adult survival compared with other areas; (4) reduced age of first breeding, reflecting the removal of adults from nesting territories and their replacement by birds in immature plumage; (5) greater levels of disappearance of satellite‐tracked birds on grouse moors than elsewhere; and (6) the finding of poisoned baits and traps, and shot or poisoned carcasses of raptors. Not all these types of evidence are available for every species, and other types of evidence are available for some. The Common BuzzardButeo buteois currently the most numerous raptor in Britain and also seems to be killed in the greatest numbers. Other raptor species, including MerlinFalco columbarius, Common KestrelFalco tinnunculusand Eurasian SparrowhawkAccipiter nisuswhich nest on or near grouse moors, have little or no significant impact on grouse and are killed less often or not at all. In the absence of illegal killing, some raptor species breed as well or better on grouse moors than in other habitats. Merlins, in particular, seem to thrive on grouse moors, benefiting from the management involved (including predator control). Other aspects of illegal raptor killing are discussed, including suggestions for ways in which it might be reduced.

Seasonal Dynamics of Testosterone and Corticosterone in Predatory Birds as Exemplified by the Northern Goshawk (Accipiter gentilis).

Testosterone and corticosterone are steroid hormones that regulate various aspects of bird behavior. The dynamics of blood level of these hormones depending on the stage of the life cycle have been studied in many species. It has been shown for both sexes that the levels of both hormones rise during the breeding season. We have studied changes in the level of these hormones in the northern goshawk (Accipiter gentilis) during a year. This has been the first study of this type on northern goshawk. We collected blood samples from 16 adult northern goshawks kept in pairs in aviaries in the VITASFERA Rare Bird Species Breeding Center. The testosterone level rises in males during the period of lekking and mating (March-June); however, there is no synchronous increase in females. The corticosterone level generally remains high throughout the year in both sexes. Since these are the only data on the northern goshawk, it cannot be concluded whether this is characteristic of the species as a whole or only for captive birds.

Northern Goshawk (Accipiter gentilis) Home Ranges, Movements, and Forays Revealed by GPS-Tracking

Northern Goshawk (Accipiter gentilis) Home Ranges, Movements, and Forays Revealed by GPS-Tracking

Pheomelanin synthesis varies with protein food abundance in developing goshawks.

The accumulation of the amino acid cysteine in lysosomes produces toxic substances, which are avoided by a gene (CTNS) coding for a transporter that pumps cystine out of lysosomes. Melanosomes are lysosome-related organelles that synthesize melanins, the most widespread pigments in animals. The synthesis of the orange melanin, termed pheomelanin, depends on cysteine levels because the sulfhydryl group is used to form the pigment. Pheomelanin synthesis may, therefore, be affected by cysteine homeostasis, although this has never been explored in a natural system. As diet is an important source of cysteine, here we indirectly tested for such an effect by searching for an association between food abundance and pheomelanin content of feathers in a wild population of Northern goshawk Accipiter gentilis. As predicted on the basis that CTNS expression may inhibit pheomelanin synthesis and increase with food abundance as previously found in other strictly carnivorous birds, we found that the feather pheomelanin content in nestling goshawks, but not in adults, decreased as the abundance of prey available to them increased. In contrast, variation in the feather content of the non-sulphurated melanin form (eumelanin) was only explained by sex in both nestlings and adults. We also found that the feather pheomelanin content of nestlings was negatively related to that of their mothers, suggesting a relevant environmental influence on pheomelanin synthesis. Overall, our findings suggest that variation in pheomelanin synthesis may be a side effect of the maintenance of cysteine homeostasis. This may help explaining variability in the expression of pigmented phenotypes.

Pigeon and Poultry Breeders, Friends or Enemies of the Northern Goshawk Accipiter gentilis? A Long-Term Study of a Population in Central Poland.

Simple SummaryThe population of goshawks crashed in the middle of the 20th century due to persecution, forest management practices, and the usage of toxic pesticides (DDT) in agriculture. Now, it has rebuilt, yet the population trend is not equal across countries. Here, we focused on a goshawk population in central Poland for which monitoring started in the 1980s (high densities were recorded at that time of 16.3 pairs/100 km2) to see how changing environmental factors influenced the current population trend. In the field and forest mosaic, these birds build their nests in small forest complexes, but important prey tend to be caught near farmsteads. This has previously resulted in the persecution of the birds by farmers. Anthropogenic food (poultry and domestic pigeons) played a key role in their population density. Consequently, when the anthropogenic food base was limited (due to changes in the Polish farmland), population abundance dropped by half. As supplementary prey (including small-game and most corvid species) were not abundant, goshawks could not replace their staple food of anthropogenic origin. This demonstrates the complex way in which socioeconomic changes in agriculture can influence a raptor population: both positively (fewer cases of persecution are being recorded now) and negatively (small-scale breeding of pigeons and poultry became unimportant and unprofitable, and small game abundance decreased due to changes in farming practices and farmland structure). In this study, we focused on a goshawk population in central Poland (study area 105 km2, forests 24 km2, seven small forest complexes) which was monitored long-term (with high densities recorded in the 1980s of 16.3 pairs/100 km2 despite persecution by farmers) to analyse how environmental factors (prey availability and changes in the forest structure) influenced population abundance, breeding parameters, and diet composition. The study was undertaken from 2011–2018, and the results were compared with published data from two previous study periods (1982–1992 and 2001–2003). The number of breeding pairs dropped from 17.1 to 8.0; the breeding success was around 75% in all study periods. The selection of nesting trees followed the changes in stand species and age structure. More nesting attempts per one nest were recorded in the current time period (1.7 vs. 1.1), which probably reflected lower anthropopressure (i.e., no cases of persecution were recorded in this study). Diet composition seemed to follow changes in the prey availability: The share of domestic pigeons and poultry (the main prey in the 1980s) as well as small game dropped, while the share of Eurasian jay and wood pigeon increased. Our studies suggested that anthropogenic food (poultry and domestic pigeons) played a key role for the goshawk population in the transformed habitats of the field and forest mosaic.

Prey Items Delivered to Young Northern Goshawks Accipiter gentilis by a Single Pair Breeding in Central Tokyo, Japan

We examined the diet of young Northern Goshawks Accipiter gentilis before and after fledging through the direct observation of prey items delivered by a single pair breeding in central Tokyo. Observations were conducted from 13 May to 14 August 2015. Three hundred prey items primarily belonging to five bird species and two genera of mammals were recorded both before and after fledging. The species contributing most to the total diet were White-cheeked Starling Spodiopsar cineraceus and Feral Pigeon Columba livia, with pigeons contributing most to total biomass followed by White-cheeked Starling. Prey item composition differed between the periods before and after fledging. After fledging, the contribution of White-cheeked Starling to the diet decreased, whereas that of pigeon increased.