Richard J. Hall’s research while affiliated with University of Georgia and other places

In urban areas, animals often aggregate at higher densities, move less, and alter their diets to consume anthropogenic food, all of which can affect wildlife health and the transmission of infectious diseases. However, it is unknown whether short-term changes in behavior associated with urban resources scale up to more pervasive long-term behavioral changes across landscape types. In this study, we used observational field data to explore how food provisioning affects behaviors relevant to parasite transmission in American white ibis (Eudocimus albus), a waterbird that has recently habituated to urban habitats and anthropogenic food. We found that ibis flock densities more than doubled during short intervals when birds were actively provisioned with food. We then explored activity budgets among urban sites with different levels of provisioning, and found that foraging time decreased with flock size and provisioning levels. Lastly, we compared ibis behavior in more natural wetland sites against urban sites, and found minimal to no differences in behaviors measured here. These results suggest that urbanization and provisioning alter ibis behaviors in ways that could influence, e.g. exposure to parasites in the short-term, but this has not yet resulted in significant long-term changes in activity budgets. Further studies of how urbanization and intentional feeding influences wildlife behavior can inform management strategies to benefit both wildlife and human health.

Spatial overlap between animals in wildlife populations can have important implications for pathogen transmission. Ecological factors and animal demographic traits can influence animal space use and spatial overlap, but it is unclear how these interactions drive pathogen transmission. We experimentally manipulated wild bank vole populations via resource supplementation and anthelmintic treatment. Using network analysis, we investigated the relationship between spatial overlap and infection probability of an endemic zoonotic hantavirus, including how vole sex and reproductive status interact with spatial behaviour to affect infection probability. Spatial overlap in a previous month drove current hantavirus infection probability, and food supplementation and anthelmintic treatment altered the effects of spatial overlap on infection probability. Vole sex and reproductive status were important factors determining whether spatial overlap increased or decreased the probability of hantavirus infection and interacted with resource supplementation and anthelmintic treatment, generating different infection dynamics in each treatment. Our research provides rare empirical evidence linking previous spatial overlap to current infection status in wildlife populations, with implications for understanding zoonotic exposure risk for humans. We further highlight the importance of incorporating variation in ecological factors and host demography when studying pathogen transmission in wildlife systems.

Animal space use and spatial overlap can have important consequences for population‐level processes such as social interactions and pathogen transmission. Identifying how environmental variability and inter‐individual variation affect spatial patterns and in turn influence interactions in animal populations is a priority for the study of animal behaviour and disease ecology. Environmental food availability and macroparasite infection are common drivers of variation, but there are few experimental studies investigating how they affect spatial patterns of wildlife. Bank voles (Clethrionomys glareolus) are a tractable study system to investigate spatial patterns of wildlife and are amenable to experimental manipulations. We conducted a replicated, factorial field experiment in which we provided supplementary food and removed helminths in vole populations in natural forest habitat and monitored vole space use and spatial overlap using capture–mark–recapture methods. Using network analysis, we quantified vole space use and spatial overlap. We compared the effects of food supplementation and helminth removal and investigated the impacts of season, sex and reproductive status on space use and spatial overlap. We found that food supplementation decreased vole space use while helminth removal increased space use. Space use also varied by sex, reproductive status and season. Spatial overlap was similar between treatments despite up to threefold differences in population size. By quantifying the spatial effects of food availability and macroparasite infection on wildlife populations, we demonstrate the potential for space use and population density to trade‐off and maintain consistent spatial overlap in wildlife populations. This has important implications for spatial processes in wildlife including pathogen transmission.

Environmental temperature fundamentally shapes insect physiology, fitness and interactions with parasites. Differential climate warming effects on host versus parasite biology could exacerbate or inhibit parasite transmission, with far-reaching implications for pollination services, biocontrol and human health. Here, we experimentally test how controlled temperatures influence multiple components of host and parasite fitness in monarch butterflies (Danaus plexippus) and their protozoan parasites Ophryocystis elektroscirrha. Using five constant-temperature treatments spanning 18–34°C, we measured monarch development, survival, size, immune function and parasite infection status and intensity. Monarch size and survival declined sharply at the hottest temperature (34°C), as did infection probability, suggesting that extreme heat decreases both host and parasite performance. The lack of infection at 34°C was not due to greater host immunity or faster host development but could instead reflect the thermal limits of parasite invasion and within-host replication. In the context of ongoing climate change, temperature increases above current thermal maxima could reduce the fitness of both monarchs and their parasites, with lower infection rates potentially balancing negative impacts of extreme heat on future monarch abundance and distribution.

Fisheries and aquaculture provide food and economic security, especially in the developing world, but both face challenges from infectious disease. Here, we consider management of disease issues from a structured decision‐making perspective to examine how infectious disease can threaten seafood production and influence management decisions. For both wild fisheries and aquaculture, disease‐management objectives generally aim to mitigate the severity and economic burden of outbreaks. General management strategies include manipulating host densities, reducing system connectivity, conserving or improving habitat, and implementing direct treatments or some other biological interventions. To inform decisions, mathematical models can be used to explore disease dynamics and to forecast the potential effectiveness of alternative management actions. Developing and implementing disease‐management strategies also involve considering uncertainties and balancing competing stakeholder interests and risk tolerances. We conclude by outlining several steps for applying structured decision making that are broadly useful to decision makers facing issues related to disease.

1. Humans have a particularly strong connection with birds, driving the enormous popularity of residential bird feeding in much of the world. 2. We conducted a web search to document US state wildlife management agency responses to two recent avian disease outbreaks, finding that 23 agencies made recommendations to cease feeding wild birds in 2021–2022. 3. The psychological benefits of bird feeding for humans are well-documented but often overlooked in management decisions in response to avian disease outbreaks. 4. Likewise, ecological evidence does not necessarily support ceasing bird feeding to reduce the spread of every avian disease. 5. Ecological and social science need to be applied in tandem to ensure that well-intended guidance to cease feeding of birds does not have unintended consequences.

Individuals from multiple species often aggregate at resources, group to facilitate defense and foraging, or are brought together by human activity. While it is well-documented that host-seeking disease vectors and parasites show biases in their responses to cues from different hosts, the influence of mixed-species assemblages on disease dynamics has received limited attention. Here, we synthesize relevant research in host-specific vector and parasite bias. To better understand how vector and parasite biases influence infection, we provide a conceptual framework describing cue-oriented vector and parasite host-seeking behaviour as a two-stage process that encompasses attraction of these enemies to the assemblage and their choice of hosts once at the assemblage. We illustrate this framework, developing a case study of mixed-species frog assemblages, where frog-biting midges transmit trypanosomes. Finally, we present a mathematical model that investigates how host species composition and asymmetries in vector attraction modulate transmission dynamics in mixed-species assemblages. We argue that differential attraction of vectors by hosts can have important consequences for disease transmission within mixed-species assemblages, with implications for wildlife conservation and zoonotic disease. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’.

Abstract Seasonal migrations are fascinating and ecologically important, but many migratory species are declining as climate change and land‐use change alter the habitats used by migrants across the annual cycle. While some migratory birds use a single wintering site, others undertake large‐scale post‐migratory movements during the nonbreeding season. Technological advances that enable tracking individual birds are uncovering more examples of post‐migratory nonbreeding movements. Documenting these movements is important for conservation, which requires understanding when and where migrants use habitats throughout their range. Here, we reviewed existing literature and collected information on the post‐migratory nonbreeding movements of 92 migratory bird species from 18 orders across six continents. Among these records, the most commonly reported drivers of movements were resource availability and climate. This strong dependence of post‐migratory nonbreeding movements on birds' abiotic and biotic environments suggests that environmental change will impact the patterns of these movements and potentially the fitness of species that undertake them. We also reviewed post‐migratory nonbreeding movements in North American‐breeding thrushes from the genus Catharus to examine the drivers of these movements in five closely related migratory species. We find that species that are less territorial are more likely to use multiple sites during the nonbreeding season; however, there is little evidence for dietary, evolutionary, or environmental differences between thrush species that move during winter and those that are stationary. While we believe our study represents the most comprehensive list of species exhibiting post‐migratory nonbreeding movements to date, biases in sampling, a lack of common terminology for these movements, and the still‐nascent availability of inexpensive, lightweight tracking devices mean that there are probably more populations that undertake such movements. Future research into the consequences of post‐migratory nonbreeding movements for individual fitness and ecosystem services would advance our understanding of their conservation importance and their evolution.