Willem F. de Boer

Environmental factors influencing the spread of the highly pathogenic avian influenza H5N1 virus in wild birds in Europe

A large number of occurrences of the highly pathogenic avian influenza (HPAI) H5N1 virus in wild birds were reported in Europe. The relationship between the occurrence pattern and environmental factors has, however, not yet been explored. This research uses logistic regression to quantify the relationships between anthropogenic or physical environmental factors and HPAI H5N1 occurrences. Our results indicate that HPAI H5N1 occurrences are highly correlated with the following: the increased normalized difference vegetation index (NDVI) in December; intermediate NDVI in March; lower elevations; increased minimum temperatures in January; and reduced precipitation in January. A predictive risk map of HPAI H5N1 occurrences in wild birds in Europe was generated on the basis of five key environmental factors. Independent validation of the risk map showed the predictive model to be of high accuracy (79%). The analysis suggests that HPAI H5N1 occurrences in wild birds are strongly influenced by the availability of food resources and are facilitated by increased temperatures and reduced precipitation. We therefore deduced that HPAI H5N1 occurrences in wild birds in Europe are probably caused by contact with other wild birds and not by contact with domestic poultry. These findings are important considerations for the global surveillance of HPAI H5N1 occurrences in wild birds.

Different environmental drivers of highly pathogenic avian influenza H5N1 outbreaks in poultry and wild birds.

A large number of highly pathogenic avian influenza (HPAI) H5N1 outbreaks in poultry and wild birds have been reported in Europe since 2005. Distinct spatial patterns in poultry and wild birds suggest that different environmental drivers and potentially different spread mechanisms are operating. However, previous studies found no difference between these two outbreak types when only the effect of physical environmental factors was analysed. The influence of physical and anthropogenic environmental variables and interactions between the two has only been investigated for wild bird outbreaks. We therefore tested the effect of these environmental factors on HPAI H5N1 outbreaks in poultry, and the potential spread mechanism, and discussed how these differ from those observed in wild birds. Logistic regression analyses were used to quantify the relationship between HPAI H5N1 outbreaks in poultry and environmental factors. Poultry outbreaks increased with an increasing human population density combined with close proximity to lakes or wetlands, increased temperatures and reduced precipitation during the cold season. A risk map was generated based on the identified key factors. In wild birds, outbreaks were strongly associated with an increased Normalized Difference Vegetation Index (NDVI) and lower elevation, though they were similarly affected by climatic conditions as poultry outbreaks. This is the first study that analyses the differences in environmental drivers and spread mechanisms between poultry and wild bird outbreaks. Outbreaks in poultry mostly occurred in areas where the location of farms or trade areas overlapped with habitats for wild birds, whereas outbreaks in wild birds were mainly found in areas where food and shelters are available. The different environmental drivers suggest that different spread mechanisms might be involved: HPAI H5N1 spread to poultry via both poultry and wild birds, whereas contact with wild birds alone seems to drive the outbreaks in wild birds.

Influence of body size on coexistence of bird species

Theory suggests that body size is an important factor in determining interspecific competition and, ultimately, in structuring ecological communities. However, there is a lack of pragmatic studies linking body size and interspecific competition to patterns in ecological communities. The objective of the present study was to determine the effect of body size (mass) on competitive interactions between bird pairs and to investigate the influence of food guilds. Point-counts were carried out in nine sites every month from November 2002 to November 2003 in the Cuetzalan Region, Mexico, and we used presence/absence and abundance data for the analyses. To calculate the strength of competition we used the Angle Frequency Method to extract form factors from 20 pairwise interactions. A prototype competition interaction and random pairs were also constructed. We used clustering techniques (PCA) to calculate the dissimilarity scores (distances, D) of each of the pairwise interactions to the prototype competition and random pairs and one-way ANOVA to test for differences between the means of the random and competitive pairs. The ratio in body mass (lnBM) for each of the interacting pairs was calculated, and the association between the lnBM ratio and the strength of competition (D) was tested using a Pearson product-moment correlation coefficient. To test for the influence of foraging guilds we used a univariate general linear model. Our results demonstrate a significant negative relationship between bird body mass ratio and competition strength – i.e. competition strength increased when the body masses of the birds became more similar. We did not find a significant influence of foraging guild on the relationship between body mass ratio and competition strength. On the basis of these results, we suggest that high variation in body sizes amongst sympatric species promotes coexistence in communities.

Spatial distribution of lion kills determined by the water dependency of prey species

Abstract Predation risk from lions (Panthera leo) has been linked to habitat characteristics and availability and traits of prey. We separated the effects of vegetation density and the presence of drinking water by analyzing locations of lion kills in relation to rivers with dense vegetation, which offer good lion stalking opportunities, and artificial water points with low vegetation density. The spatial distribution of lion kills was studied at the Klaserie Private Nature Reserve, South Africa. The distance between 215 lion kills and the nearest water source was analyzed using generalized linear models. Lions selected medium-sized prey species. Lion kills were closer to rivers and to artificial water points than expected by random distribution of the kills. Water that attracted prey, and not the vegetation density in riverine areas, increased predation risk, with kills of buffalo (Syncerus caffer), kudu (Tragelaphus strepsiceros), and wildebeest (Connochaetes taurinus) as water-dependent prey species. Traits of prey species, including feeding type (food habits), digestion type (ruminant or nonruminant), or body size, did not explain locations of lion kills, and no seasonal patterns in lion kills were apparent. We argue that the cascading impact of lions on local mammal assemblages is spatially heterogeneous.

Foraging Site Selection of Two Subspecies of Bar-tailed Godwit Limosa lapponica: Time Minimizers Accept Greater Predation Danger Than Energy Minimizers

Different spatial distributions of food abundance and predators may urge birds to make a trade-off between food intake and danger. Such a trade-off might be solved in different ways in migrant birds that either follow a time-minimizing or energy-minimizing strategy; these strategies have been assigned to two sub-species of Bar-tailed Godwits Limosa lapponica that use the European Wadden Sea during northward migration. At the study area on Terschelling we recorded feeding site selection, time budgets and intake rates (prey/min) in the period that both lapponica (energy minimizer) and taymyrensis (time minimizer) sub-species were present (late April till the end of May 2007). Prey availability (number of prey/m2) was negatively correlated to the distance from cover. Based on resightings of colour-ringed Bar-tailed Godwits, taymyrensis was foraging closer to cover, and for a higher proportion of time than lapponica (67% vs. 33%). During the high tide period taymyrensis was also foraging on inland coastal meadows, Moreover, taymyrensis was more vigilant than lapponica, whereas lapponica showed more resting and preening behaviour. Lapponica had a higher instantaneous intake rate, but taymyrensis had a higher overall intake rate and the birds were more successful in taking larger prey items than lapponica. Supposedly, due to the increased foraging time and additional foraging on the inland meadows, the time-minimizing taymyrensis achieved a higher fuel deposition rate than lapponica. Taymyrensis shifted towards food-rich areas, apparently accepting higher predation risks, whereas energy-minimizing lapponica avoided predation danger by foraging further from cover.

Do Arctic breeding geese track or overtake a green wave during spring migration

Geese breeding in the Arctic have to do so in a short time-window while having sufficient body reserves. Hence, arrival time and body condition upon arrival largely influence breeding success. The green wave hypothesis posits that geese track a successively delayed spring flush of plant development on the way to their breeding sites. The green wave has been interpreted as representing either the onset of spring or the peak in nutrient biomass. However, geese tend to adopt a partial capital breeding strategy and might overtake the green wave to accomplish a timely arrival on the breeding site. To test the green wave hypothesis, we link the satellite-derived onset of spring and peak in nutrient biomass with the stopover schedule of individual Barnacle Geese. We find that geese track neither the onset of spring nor the peak in nutrient biomass. Rather, they arrive at the southernmost stopover site around the peak in nutrient biomass, and gradually overtake the green wave to match their arrival at the breeding site with the local onset of spring, thereby ensuring gosling benefit from the peak in nutrient biomass. Our approach for estimating plant development stages is critical in testing the migration strategies of migratory herbivores.

Dilution effect in bovine tuberculosis: risk factors for regional disease occurrence in Africa

Changes in host diversity have been postulated to influence the risk of infectious diseases, including both dilution and amplification effects. The dilution effect refers to a negative relationship between biodiversity and disease risk, whereas the amplification effect occurs when biodiversity increases disease risk. We tested these effects with an influential disease, bovine tuberculosis (BTB), which is widespread in many countries, causing severe economic losses. Based on the BTB outbreak data in cattle from 2005 to 2010, we also tested, using generalized linear mixed models, which other factors were associated with the regional BTB presence in cattle in Africa. The interdependencies of predictors and their correlations with BTB presence were examined using path analysis. Our results suggested a dilution effect, where increased mammal species richness was associated with reduced probability of BTB presence after adjustment for cattle density. In addition, our results also suggested that areas with BTB infection in the preceding year, higher cattle density and larger percentage of area occupied by African buffalo were more likely to report BTB outbreaks. Climatic variables only indirectly influenced the risk of BTB presence through their effects on cattle density and wildlife distribution. Since most studies investigating the role of wildlife species on BTB transmission only involve single-species analysis, more efforts are needed to better understand the effect of the structure of wildlife communities on BTB dynamics.

A comparison of faecal analysis with backtracking to determine the diet composition and species preference of the black rhinoceros (Diceros bicornis minor)

The diet of black rhinoceros (Diceros bicornis minor) was studied using backtracking and faecal analysis in South Africa. Both methods yielded different results, with a large bias for dominant species. Results of backtracking showed that the rhinos browsed on 80 plant species. Grasses comprised 4.5% of the diet in the faecal analysis, but were not recorded during the backtracking. The backtracking method, along with a measure of forage availability, was used to identify two groups of plant species, those species taken in a higher proportion than available in the field and those taken in a lower proportion. Chemical analyses showed that these two species groups were similar in in vitro digestibility, macro-elements and fibre constituents. Mean bite size and species contribution to the diet were not correlated with any of the forage quality parameters, indicating that rhinos were not maximising nutrient intake or minimising fibre intake of these consumed plant species.

Tropical Secondary Forest Management Influences Frugivorous Bat Composition, Abundance and Fruit Consumption in Chiapas, Mexico

Most studies on frugivorous bat assemblages in secondary forests have concentrated on differences among successional stages, and have disregarded the effect of forest management. Secondary forest management practices alter the vegetation structure and fruit availability, important factors associated with differences in frugivorous bat assemblage structure, and fruit consumption and can therefore modify forest succession. Our objective was to elucidate factors (forest structural variables and fruit availability) determining bat diversity, abundance, composition and species-specific abundance of bats in (i) secondary forests managed by Lacandon farmers dominated by Ochroma pyramidale, in (ii) secondary forests without management, and in (iii) mature rain forests in Chiapas, Southern Mexico. Frugivorous bat species diversity (Shannon H’) was similar between forest types. However, bat abundance was highest in rain forest and O. pyramidale forests. Bat species composition was different among forest types with more Carollia sowelli and Sturnira lilium captures in O. pyramidale forests. Overall, bat fruit consumption was dominated by early-successional shrubs, highest late-successional fruit consumption was found in rain forests and more bats consumed early-successional shrub fruits in O. pyramidale forests. Ochroma pyramidale forests presented a higher canopy openness, tree height, lower tree density and diversity of fruit than secondary forests. Tree density and canopy openness were negatively correlated with bat species diversity and bat abundance, but bat abundance increased with fruit abundance and tree height. Hence, secondary forest management alters forests’ structural characteristics and resource availability, and shapes the frugivorous bat community structure, and thereby the fruit consumption by bats.

The use of statistical tools in field testing of putative effects of genetically modified plants on nontarget organisms

Abstract To fulfill existing guidelines, applicants that aim to place their genetically modified (GM) insect-resistant crop plants on the market are required to provide data from field experiments that address the potential impacts of the GM plants on nontarget organisms (NTOs). Such data may be based on varied experimental designs. The recent EFSA guidance document for environmental risk assessment (2010) does not provide clear and structured suggestions that address the statistics of field trials on effects on NTOs. This review examines existing practices in GM plant field testing such as the way of randomization, replication, and pseudoreplication. Emphasis is placed on the importance of design features used for the field trials in which effects on NTOs are assessed. The importance of statistical power and the positive and negative aspects of various statistical models are discussed. Equivalence and difference testing are compared, and the importance of checking the distribution of experimental data is stressed to decide on the selection of the proper statistical model. While for continuous data (e.g., pH and temperature) classical statistical approaches – for example, analysis of variance (ANOVA) – are appropriate, for discontinuous data (counts) only generalized linear models (GLM) are shown to be efficient. There is no golden rule as to which statistical test is the most appropriate for any experimental situation. In particular, in experiments in which block designs are used and covariates play a role GLMs should be used. Generic advice is offered that will help in both the setting up of field testing and the interpretation and data analysis of the data obtained in this testing. The combination of decision trees and a checklist for field trials, which are provided, will help in the interpretation of the statistical analyses of field trials and to assess whether such analyses were correctly applied. We offer generic advice to risk assessors and applicants that will help in both the setting up of field testing and the interpretation and data analysis of the data obtained in field testing.