Bird Density Research Articles

Population Density and Stability of Breeding Birds in English Oak Woodland Over a 32-Year Period in Relation to Habitat Structure and Edges

Long-term breeding bird censuses in Białowieża National Park (BNP), north-east Poland, have revealed rather low densities of birds and high community stability which may be features of near-natural forest conditions. This paper reports on a long-term census of breeding birds in 50 ha of oak woodland in central England which contained both managed and undisturbed areas. New information is provided on breeding bird density and its spatial variation within English mature broadleaved woodland to address two questions: Under what circumstances are English woods likely to support higher densities than those occurring in BNP? Is there evidence that population and community stability is lower in English woodland? The overall bird density was lower than in the BNP oak-hornbeam stands, at the scale of both the whole study area and the undisturbed stands. Densities of three of the five dominant species (Cyanistes caeruleus, Parus major, Troglodytes troglodytes) were lower in BNP, Fringilla coelebs was higher, while Erithacus rubecula was similar. Within the undisturbed stands, densities of seven of 12 species, including T. troglodytes, were similar to those in BNP, two were considerably higher (C. caeruleus, P. major) and one much lower (F. coelebs). Selection of the external woodland edge by several species resulted in relatively high overall densities in the edge zone. The broad composition of the bird community remained fairly stable with the exception of declines in tropical migrants and increases in shrub layer nesters. Temporal abundance patterns of species showed much individuality. Trends of several species appeared to be driven by changes in habitat structure. However, the same species remained numerically dominant or characteristic of the wood throughout the study period. This suggests there was a core of resilient species, much as proposed for BNP. Although caution is needed in drawing conclusions from a single site, with the exception of a small number of species, in recent decades there is unlikely to have been a general pattern of higher densities of birds in English woodland than in BNP. However, some English woods with highly complex vegetation structures, or a high proportion of edge habitat, do have exceptionally high densities (> 100 territories/10 ha).

Absolute Densities of Breeding Birds in Estonian Forests: A Synthesis

This paper synthesizes all available quantitative information on total breeding densities of Estonian forest bird assemblages, as estimated in territory mapping studies since the 1950s. There have been two approaches, one based on multiple visits (typically 7–8), and the other of reduced effort, developed for long-term monitoring. Compared to these mapping methods, line (strip) transects give ca. 30% lower estimates; they also vary widely. After quality checking, a total of 90 mapping estimates were extracted. The estimates were then integrated into ‘typical densities’ by habitat types, after critically assessing data quality and bias. ‘Typical density’ is conceptualized as a range of common density values in actual topographic, soil, forest-age and landscape conditions, under minor recent thinning influence. It also considers 15–20% underestimation of the territory mapping, which was demonstrated using a case study on post-breeding nest searching of three thrush (Turdus spp.) species. The Estonian forest bird densities show monotonous increases along the stand age, following three alternative shapes related to site productivity: a major increase within 100 years in the most productive forests, a delayed increase (also post 100 years) in pine forests of medium productivity, and slow and slight increases at low-productivity sites. Such density estimates can serve as a basis to analyse deviations in particular conditions and be integrated into land-use scenario-modelling tools across landscapes. It is important to keep the territory mapping approaches to bird census in active use and development, since several issues in conservation and ecosystem functioning cannot be addressed by relative assessments.

Recent population size of Timor Friarbird and resources utilization at three landscapes in West Timor Island, Indonesia

The Timor Friarbird is an endemic species of Timor Island that plays an important role in forest ecosystems, agriculture and other natural environments in the semiarid region. Although classified as an endemic species and declining population, the bird is protected by Indonesian law. This study aims to assess the density, group size, and population distribution of Timor Friarbird and resource uses in three landscape at Western Timor. Distance sampling methods with transect lines was used to estimate population density and bird distribution. The highest estimated bird population density (3.31 ind./ha) in the Baumata landscape and lowest (0.15 ind./ha) in Bipolo. Individual sizes per group of 1-4 individuals in all landscapes. Utilization of distributed feed resources in the main area, secondary and low potency area. The distribution of species in the rainy season is higher found in low-lying, higher dry seasons in lowlands. High anthropogenic pressures and changes in dominant habitats in the low-lying west Timor Island contribute to the rate of population decline of this species thus impacting crop productivity and conservation efforts of this species in the future.

Leaving more than footprints: Anthropogenic nutrient subsidies to a protected area

AbstractMobile animals that traverse ecosystem boundaries can fundamentally reshape environments by providing critical nutrient and energy inputs to the ecosystems they inhabit. In particular, aggregations of seabirds often transform coastal and island ecosystems through large amounts of nutrient‐rich guano deposition. Anthropogenically driven losses of these subsidies can occur through changes in abundance of mobile species, including seabirds, and have been shown to drive whole‐scale ecosystem state change on islands. However, even though many species that forage on anthropogenic food sources are highly mobile and may thus play important roles in moving nutrients from urban systems to otherwise conserved ecosystems, the impacts of anthropogenic supplements on spatial subsidies have been largely ignored. Here we examine the effects of large nesting colonies of Western Gulls (Larus occidentalis), a generalist carnivore known to forage on human refuse, on the Channel Islands of California. Specifically, we explore how their foraging on human subsidies may change nutrient deposition patterns at their relatively remote and protected breeding islands. We equipped gulls with GPS loggers to assess the frequency of urban foraging, and we partnered this tracking data with bird density data to estimate the rate of wild and urban‐derived guano deposition on two different islands. Consistent with research on other gull species, we found high (up to 40%) but island‐specific rates of urban foraging, resulting between 66 and 93 kg ha−1 of guano in these two sites during the breeding season, a level greater than half the amount of fertilizer applied annually in typical commercial agricultural settings and likely the primary source of nitrogen and phosphorus inputs to this system. Specifically, we estimate that 27 kg ha−1 year−1 of nutrient‐rich guano is shuttled to these otherwise isolated islands from anthropogenic sources. This research highlights the large shadow (i.e., footprint) that human activity can cast on even remote ecosystems by driving significant nutrient enrichment through impacts on animal behavior and connectivity.

Effect of stocking density and vitamin E or zinc supplementation on growth, physiology, gene expression, and economic efficiency of growing broiler chicks

A total of 636 1-day-old male Cobb chicks were randomly assigned to seven treatments. The chicks were offered feed and water ad libitum throughout the experimental period. The first three groups included different stocking densities of broiler birds (low stocking density, LSD: 23 kg/m2; medium stocking density, MSD: 34 kg birds/m2; and high stocking density HSD: 39 kg birds/m2). The LSD group was considered a control group. The other four groups included MSD or HSD broiler birds supplemented with either Vit E (100 mg/kg DM diet; MSDVE and HSDVE) or Zn (100 mg/kg DM diet; MSDZn and HSDZn) in their basal diet. The main findings indicated that HSD and MSD negatively affected (p < 0.05) all variables under investigation compared with LSD. Compared with LSD, broiler birds in the MSD and HSD groups had lower body weights and higher feed conversion ratios, higher concentrations of blood plasma hormones (triiodothyronine thyroxine and corticosterone), and downregulated expression levels of hepatic growth hormone and insulin-like growth factor-l. In addition, broiler birds stocked at medium or high densities resulted in less economic return and profit. Vit E or Zn supplementation to broiler birds stocked at medium or high densities significantly reversed all adverse effects of HSD (> 23 kg/m2) on growth performance, hormones, and gene expression. It could be recommended that adding Zn at a level of 100 mg/kg per DM diet allows increasing the stocking density of broiler birds from 23 kg/m2 to 34 birds/m2 while maintaining the birds, welfare and economic profit.

Comparison of avian community assembly and its disease transmission risk between urban and surrounding rural area in Shanghai, China

Urbanization has expanded rapidly worldwide in recent decades, and has led to a series of environmental changes. With the improvement of the urban habitat, the density of wildlife is on the rise, especially for the birds. However, birds are host to a variety of viruses, pathogenic microorganisms and parasites, and the increase of their density may amplify the risk of disease transmission in cities. Thus, understanding the characteristics of regional bird community aids the integration of knowledge about the risk of disease transmission by birds. Here, we conducted a field survey in summer, 2021, to compare the differences in vegetation, species richness and individual numbers of bird in Shanghai urban and surrounding areas covering 28 zones along an urbanization gradient and to assess the possibility of bird transmission risk in Shanghai. We recorded 122 plant species and 3416 bird individuals of 23 species. Our results found that urbanization has led to a decline in bird species and densities than relatively pristine habitats (rural, agroforestry habitat, urban park), and based on our literature collection, most species carrying avian influenza virus were migratory waterbirds (anatidae and shorebird) that relatively away from urban area. Our study suggests that urbanization reduces bird diversity, but urban birds may have a low probability of transmitting the avian influenza virus to humans.

Density surface and excursion sets modeling as an approach to estimating population densities

AbstractEffective species management and conservation require knowledge of species distribution and status. We used point‐transect distance sampling surveys of the endangered palila (Loxioides bailleui), a honeycreeper currently found only on the Island of Hawai'i, USA, to generate robust estimates of total abundance and simultaneously model the distribution, abundance, and spatial correlation of the species as a density surface model (DSM). Point‐transect distance sampling is a widely applied method to estimate bird densities accounting for imperfect detection probability. For the DSM we used a generalized additive model framework and soap film smoothers to control the effects of boundary features. This modeling approach allowed us to account for imperfect detection and propagate detection probability uncertainty. We compared the uncertainty in palila abundance estimates using standard point‐transect distance sampling to estimates from the DSM. The DSM, accounting for both distance‐sampling‐derived detection probability variance and the generalized additive model density estimate variance, did not improve population estimator precision; however, it provided insight into the species' distribution, density, and uncertainty. We also applied excursion sets analysis to objectively identify areas where the species occurs in high densities. The 2017 global population of &lt;2,000 individuals was limited to an excursion area of 1,500 ha. Our findings can help management and regulatory agencies by simultaneously mapping a species' distribution and density, improving survey protocols, and providing information important to species conservation.

Ecological Sustainability at the Forest Landscape Level: A Bird Assemblage Perspective

Maintaining landscape integrity in terms of ecological functions is a key principle of sustainable forest management. Bird assemblages use all parts of forest landscapes and provide an opportunity to analyze their broad-scale integrity in those regions where bird census data are of sufficient quality and detail. In this study, I modelled likely landscape-composition consequences of different scenarios of even-aged (clear-cutting-based) silviculture on breeding-bird assemblages. The models were parameterized using high-quality territory-mapping data from Estonia. I considered three approaches for obtaining the model parameters. Of these, (i) a formal analysis of rank-abundance curves was rejected due to the inconsistency of the curve shapes among habitat types. Two other approaches were used and complemented each other: (ii) smoothed forest-type specific functions of total assemblage densities along post-clear-cut succession, and (iii) empirical average densities of each species by forest type and age class (for species composition analyses). The modelling revealed a parallel loss of bird densities and, to a lesser extent, of species at shorter rotations; currently, this effect is disproportionately large on productive soils. For conserving the productive hotspots, the 30% protection target of the EU Biodiversity Strategy overperformed other scenarios. In all landscape settings, typologically representative old-forest reserves (even artificially drained stands) helped to mitigate rotational forestry. The potential of even-aged production forestry to host early-successional species was already realized at much longer rotations than currently (given uniform stand-age structure). Comparing potential and realized bird assemblages provides a tool for assessing ecological integrity at the landscape scale, and the results can be used for elaborating regional management goals of ecologically sustainable forestry.

Population densities of birds breeding in an urban environment dominated by allotment gardens and other ‘green’ areas in a Central European city

Abstract A total of 50 breeding bird species were recorded in 2017 in an urban environment (589 ha) in the city of Wrocław, SW Poland. This environment was dominated by green habitats, such as allotment gardens (41.2%), parklnds (13.4%) and forests (2.7%). For 41 species, population densities were estimated. A high population densities were recorded for Phoenicurus phoenicurus (9.2 pairs / 100 ha), Sylvia atricapilla (7.3), Turdus merula (6.6), Phoenicurus ochruros (6.3), Luscinia megarhynchis (5.3.), Sylvia curruca (4.1) and Serinus serinus (3.7). In the alltment gardens, much higher population density of Pica pica (14.5) than Corvus cornix (6.5); and higher population density of Columba palumbus (2.8) than Streptopelia decaocto (1.2) were recorded.

Diversity of fauna species in the mangrove ecosystem of Youtefa Bay Tourism Park, Papua, Indonesia

Abstract. Sari A, Tuwo A, Saru A, Rani C. 2022. Diversity of fauna species in the mangrove ecosystem of Youtefa Bay Tourism Park, Papua, Indonesia. Biodiversitas 23: 4490-4500. Youtefa Bay Tourism Park is a mangrove ecosystem in Jayapura City, Papua, Indonesia with high importance for biodiversity conservation as well as providing livelihood for local communities. Yet, information regarding the biological diversity of the mangrove ecosystem is lacking. This information is important to assess the state of the mangrove and to support its sustainable management of this area. This research aimed to determine the faunistic diversity of Youtefa Bay Tourism Park. The research was conducted from August 2019 to February 2020 using line transect method with quadrant to record species and the number of individuals. The results showed that in the studied area there were six, five and 27 species of birds, reptiles and macrozoobenthos, respectively. The density of birds ranged from 2.35-23.94 ind/ha with Sterna hirundo of the Sternidae family having the highest density. The reptile species density ranged between 20 and 66.67 ind/ha, while the most common macrozoobenthos species were from Gastropoda and Pelecypoda classes. The highest and lowest relative abundance for birds were S. hirundo and Sula lencogastes with 20% and 5%, while that of reptiles were Mabouya sp. and Varanus salvadorii with 37% and 15%, and for macrozoobenthos species were Duplicaria duplicata and Solen sp. with 9.93% and 0.35%, respectively. The Diversity Index (H’) of birds, reptiles, and macrozoobenthos ranged of 0.29-1.39, 0.27-1.61, and 2.92-3.04, respectively. The diversity index was as low at Abepantai and Youtefa Bay Pier, while moderate at Tobati, Enggros, and Nafri Villages. Water quality parameters indicated that the waters in Youtefa Bay Tourism Park were still suitable for the survival of biota and the preservation of the mangrove ecosystem. The results of this study might be useful for monitoring the status of the mangrove ecosystem in the future and for baseline information in developing sustainable management of Youtefa Bay Tourism Park.

Bird species composition, density and feeding guilds in contrasting lowland dipterocarp forests of Terengganu, Peninsular Malaysia

A study was conducted to determine the species composition, density and feeding guild of birds at Tasik Kenyir and Setiu, Terengganu between June and September 2017 using line transect method. Observations of birds at Tasik Kenyir and Setiu recorded a total of 297 individuals consisting of 26 families from 64 species. This study estimated that the diversity of birds at Tasik Kenyir (H’ = 3.6) was higher compared to Setiu (H’ = 2.9). However, the density of birds at Setiu (52.05 ± 9.09 SE individuals/ha) was higher than Tasik Kenyir (37.56 ± 10.28 SE individuals/ha). Ten feeding guilds of birds were identified in this study; insectivore, nectarivore, frugivore, omnivore, carnivore, granivore, insectivore-nectarivore, insectivore-frugivore, insectivore-granivore and frugivore-granivore. This study has provided valuable information on the bird assemblage and the understanding on the distribution of birds at Tasik Kenyir and Setiu. It is highly recommended that further studies to be conducted at both sites with more sampling efforts in order to gain a more comprehensive baseline datasets for monitoring bird population trends and turnover between habitats.

Epidemiological Features of the Highly Pathogenic Avian Influenza Virus H5N1 in a Densely Populated Area of Lombardy (Italy) during the Epidemic Season 2021-2022.

In the last two years, there have been three major epidemic seasons in the territory of the European Union and the HPAI epizootic in 2021–2022 is the most severe in recent history. In Italy, the disease was introduced to dense poultry areas with serious economic consequences for the entire sector. In Lombardy, the analysis of the risk factors was carried out, also taking into account the density of domestic birds. In the most affected areas, 66.7% of the outbreaks occurred in the areas with the highest poultry density and the likelihood of an outbreak occurring increased with an increase in the density of birds per km2. In cells 10 × 10 km with a density greater than 10,000 birds/km2, the probability of outbreak occurrence was over 66.7%. The provinces involved in the last epidemic were the same involved in previous epidemics and, given the risk factors present in the area, it is plausible that the risk remains high also for future epidemic seasons. Therefore, to avoid the repetition of similar events, certain control measures shall be strengthened and vaccination considered as a complementary tool for the control of HPAI virus in risk areas.

Assessment of Avian Biodiversity and Bird strikes to Aircrafts at Bacha Khan International Airport, Peshawar KP, Pakistan

Birds inside or outside the airport is big threat to the aircraft. The main objective of this study was toidentify hazards of bird species, population density and richness of birds around BACHA KHANINTERNATIONAL AIRPORT. The methods being used were point count/vantage point method for thepopulation estimation. The Study was based upon two sites (Site A Airport Premises) spreading over anarea of 30 acres and (Site B which is within Airport) spreading over an area of 7.5 Acres. Total Samplingpoints (Observation Points) were 120 and every sampling point was visited for 15-20 minutes and birdswere counted for three to five minutes in a fixed radius. Transact line method spreading over 500 meterswas used to analyze the data. Birds were observed every 100 meters. Primary and Secondary data wascollected using questionnaire. The study identified the reasons for Bird Air strikes at the Airport and exploredpossible mitigation measures of avian hazards in Peshawar airport premises. This data will be useful forthe aviation authorities in preparing managed bird control program. In this study hypothesis were given incomparison with other attractants tree attracts more birds in Peshawar Airport. Averages of 30 specieswere observed in Site A and 15 in Site B monthly respectively. The highest Relative Abundance observed atSite A was of House Crow species which is 16.8463612% and in Site B Kite species with relative abundance21.4953271%. The Highest number of Bird strike occurred at Runway followed by strikes outside the fencewith reference to Bird strike report 2021-22. Pigeon and Doves were observed in Flight over the airportpremises. 36 Bird’s diversity observed around airport in rainfall and cloud cover assessed through Shannondiversity index as 3.024 which indicate good diversity of birds in the study area which might be a potentialthreat to the aircraft? The study revealed that effective management plan should also be taken intoconsideration. The Population density of Site A outside the airport premises (30 Acres) is 24.13/Acre andfor Site B within Airport which is 7.5 Acres is 14.2/Acre respectively.

In the bleak mid-winter: The value of brownfield sites for birds during the winter

Brownfield sites (e.g., wastelands, disused industrial grounds and power stations) are valuable refuges for urban birds during the breeding season. This owes to the presence of vegetation in different stages of succession, which provide a high diversity of food and breeding resources. However, insufficient research has explored their winter value, when temperatures are lower and food is scarcer. Accordingly, 342 bird and habitat surveys were conducted in brownfield sites, and other land-uses, across Greater Manchester. Bird density estimates were then calculated using Distance software and bird-habitat associations were analysed using Canonical Correspondence Analysis (CCA). Moreover, the impact of brownfield site development on winter bird density from 2000 to 2009 in Greater Manchester was explored using the bird density estimates, and historical image function in Google Earth. In brownfield sites, Pica pica had the highest density estimate (142 per km2), although four species had estimated densities > 100 per km2 (Turdus merula; Cyanistes caeruleus; Passer domesticus; Aegithalos caudatus). The CCA indicated that Aegithalos caudatus, Cyanistes caeruleus, Parus major, Prunella modularis were associated with Fagus sylvatica, Betula pendula, and Buddleja davidii on brownfield sites, which during the winter 1) produce seeds 2) support overwintering insects, providing a valuable food source. Nevertheless, across land-uses, most species favoured green space and pre-2000 housing. Brownfield sites were most replaced between 2000 and 2009, with 17.8 km2, 14.9 km2, and 12 km2 replaced by commercial, industrial, and post-2000 housing respectively. This is likely to have had a negative impact on the winter density of most bird species, owing to 1) the removal of brownfield site vegetation 2) increases in impervious land cover. Future declines in winter bird abundance could be mitigated by retaining brownfield site vegetation and setting aside brownfield sites in close proximity to green space and pre-2000 housing.

Tree and hedgerow configurations on maize farms are key drivers of granivorous passerine bird assemblage patterns

Granivorous birds are responsible for significant cereal crop losses to farmers worldwide. However, how cropland vegetation structural features contribute to granivorous birds’ presence and assemblage patterns remains poorly understood. This study explores how granivorous bird distribution in terms of abundance similarities, densities, species richness and encounter rates, respond to habitat configuration elements and cropping methods across non Bt-maize fields. Here we compare nine intercropped to seven monoculture farms within which influence of eight vegetation structural features and two general habitat attributes on granivorous bird’s assemblages were determined across three maize growing seasons. Bird abundance similarities were most significantly influenced by heights of hedgerows and trees. For assemblage composition, whereas bird species richness was unaffected by any habitat variable, encounter rates were higher on farms with higher hedges or tall trees. On the other hand, bird densities increased on farms with abundant large mature trees, large woodlots, high hedgerows or dominance of indigenous trees, but diminished with both overall tree density and young-tree abundance. These results suggest that keeping hedgerows low, minimizing woodlot sizes and maintaining young isolated trees across the farm, may significantly contribute to reducing granivorous bird aggregation on maize farms thus mitigating potential for maize grain losses.

The number, behaviour, and population indices of Mallard ducks (Anas platyrhynchos L.) in non-urban and urban environments of the Lublin region

The paper presents indicators of the number, reproduction and behavior of mallard ducks living in unurbanized and urbanized environments in the Lublin region. The research carried out in urban areas and beyond showed significant changes in the behavior of birds in terms of their timidity due to the presence of humans, as well as the distance of departure of birds and re-landing on the water surface. These distances between the described types of environment were four times higher for unurbanized areas. Significantly higher numbers, and thus also the bird density indicators, were found, as well as the average size of the assemblages in urbanized areas, which, depending on the date of the study, was higher by 2.0-3.2 birds in the community in favor of anthropogenic environments. There were no significant differences in the sex structure and reproductive rates between the study sites, with male predominance in all types of environments. The conducted analyzes indicate a progressive adaptation to urbanized environments by mallard ducks. This is done through behavioral changes, which does not significantly affect the course of natural selection and breeding processes of birds in these environments, as compared to unurbanized or low-urbanized environments typical for this species until recently.

Demographic composition, post-release and natal dispersal, and breeding success of the reintroduced Oriental Stork Ciconia boyciana

Summary Species restoration through reintroduction and reinforcement is widely considered as an effective method for the conservation of threatened animals. Although these approaches have been increasingly implemented over the last half-century, many attempts have failed. Dispersal behaviour is one of the key factors determining reintroduction success. We reported the demographic composition and dispersal pattern (i.e., post-release and natal dispersal) of a reintroduced Oriental Stork Ciconia boyciana population in Japan and identified the determinants of breeding success in 2005–2019. We hypothesized that one of the key determinants of breeding success is the density-dependent effect through post-release and natal dispersal. The F1 generation occurrence corresponded to two years, F2 to seven, F3 to 11, and F4 to 14 years after initial reintroduction. Wild-born birds accounted for 74% of the reintroduced population at F4 occurrence. Post-release dispersal distances were shorter than natal dispersal. Inter-nest distance was selected as the key factor determining breeding success. These results may have been due to feeding habitat restoration and conspecific interactions. In conclusion, steady recruitment to the next generation is thought to be due to a moderate natal dispersal and the subsequent low breeding density of wild-born birds.

Density-dependence of reproductive success in a Houbara bustard population

Although density-dependent processes and their impacts on population dynamics are key issues in ecology and conservation biology, empirical evidence of density-dependence remains scarce for species or populations with low densities, scattered distributions, and especially for managed populations where densities may vary as a result of extrinsic factors (such as harvesting or releases). Here, we explore the presence of density-dependent processes in a reinforced population of North African Houbara bustard ( Chlamydotis undulata undulata ). We investigated the relationship between reproductive success and local density, and the possible variation of this relationship according to habitat suitability using three independent datasets. Based on eight years of nests monitoring (more than 7000 nests), we modeled the Daily Nest Survival Rate (DNSR) as a proxy of reproductive success. Our results indicate that DNSR was negatively impacted by local densities and that this relationship was approximately constant in space and time: (1) although DNSR strongly decreased over the breeding season, the negative relationship between DNSR and density remained constant over the breeding season; (2) this density-dependent relationship did not vary with the quality of the habitat associated with the nest location. Previous studies have shown that the demographic parameters and population dynamics of the reinforced North African Houbara bustard are strongly influenced by extrinsic environmental and management parameters. Our study further indicates the existence of density-dependent regulation in a low-density, managed population. • Density-dependency mechanisms also occur in low-density populations. • Reproductive performance is impacted by the density of birds around the nests. • Density-dependent effects do not vary in space and time.

Wild Bird Densities and Landscape Variables Predict Spatial Patterns in HPAI Outbreak Risk across The Netherlands.

Highly pathogenic avian influenza viruses’ (HPAIVs) transmission from wild birds to poultry occurs globally, threatening animal and public health. To predict the HPAI outbreak risk in relation to wild bird densities and land cover variables, we performed a case-control study of 26 HPAI outbreaks (cases) on Dutch poultry farms, each matched with four comparable controls. We trained machine learning classifiers to predict outbreak risk with predictors analyzed at different spatial scales. Of the 20 best explaining predictors, 17 consisted of densities of water-associated bird species, 2 of birds of prey, and 1 represented the surrounding landscape, i.e., agricultural cover. The spatial distribution of mallard (Anas platyrhynchos) contributed most to risk prediction, followed by mute swan (Cygnus olor), common kestrel (Falco tinnunculus) and brant goose (Branta bernicla). The model successfully distinguished cases from controls, with an area under the receiver operating characteristic curve of 0.92, indicating accurate prediction of HPAI outbreak risk despite the limited numbers of cases. Different classification algorithms led to similar predictions, demonstrating robustness of the risk maps. These analyses and risk maps facilitate insights into the role of wild bird species and support prioritization of areas for surveillance, biosecurity measures and establishments of new poultry farms to reduce HPAI outbreak risks.

Trophic interactions and feedbacks maintain intact and degraded states of Hawaiian tropical forests

AbstractFeedbacks within ecosystems can lead to internal reinforcement of the current state providing ecosystem resilience. Often, multiple biotic interactions across trophic levels play a role in such feedbacks, yet these are generally studied independently, obscuring the relative importance of interactions among different factors. We look at various potential feedbacks in intact and degraded mesic forests on Hawaiʻi Island where managers have planted native Acacia koa (koa) trees in an attempt to jumpstart succession in former cattle pastures. These restoration forests, however, have not undergone secondary succession, instead maintaining a koa overstory with an exotic pasture grass understory. We contrasted different trophic level processes that influence the capacity for natural understory regeneration: feedbacks between bird‐mediated seed rain and fruiting understory (“top‐down”), as well as links between understory composition and microhabitats for native seed germination (“bottom‐up”). We quantified bird‐mediated seed rain under canopy trees along transects spanning intact, fragmented, and restoration forests. Along these transects, we established plots around focal overstory trees to measure abundance of fruiting understory species, ground cover (e.g., exotic grass, bryophyte), and obtained estimates of bird density to evaluate the contribution of each of these factors to seedling abundance. We also used a factorial seed addition/grass removal experiment to directly compare the influence of seed rain and germination substrate. We found evidence of both top‐down and bottom‐up feedbacks that reinforced the current state of each forest type. In the intact and fragmented forests, the combination of comparatively high seed rain and ample germination substrate is likely critical for maintaining a diverse forest system. In contrast, exotic grasses exhibit priority effects in restoration forests, inhibiting seed germination and effectively negating any benefits that could be derived from bird‐mediated seed rain. Such internal reinforcement suggests that active, rather than passive, restoration would be beneficial to increase forest diversity in restoration areas.