Wildlife infectious disease dynamics in the context of seasonality and bird migration

The thesis contains chapters that elucidate questions with regards to wildlife infectious disease dynamics - avian influenza in particular - and how those dynamics are affected by seasonality and avian migration

Flexible reaction norms to environmental variables along the migration route and the significance of stopover duration for total speed of migration in a songbird migrant

Background Predicting the consequences of continuing anthropogenic changes in the environment for migratory behaviours such as phenology remains a major challenge. Predictions remain particularly difficult, because our knowledge is based on studies from single-snapshot observations at specific stopover sites along birds’ migration routes. However, a general understanding on how birds react to prevailing environmental conditions, e.g. their ‘phenotypic reaction norm’, throughout the annual cycle and along their entire migration routes is required to fully understand how migratory birds respond to rapid environmental change. Results Here, we provide direct evidence that northern wheatears (Oenanthe oenanthe) from a breeding population in Alaska adjusted their probability to resume migration as well as the distance covered per night, i.e. travel speed, to large-scale environmental conditions experienced along their 15,000 km migratory route on both northwards and southwards migrations. These adjustments were found to be flexible in space and time. At the beginning of autumn migration, northern wheatears showed high departure probabilities and high travel speeds at low surface air temperatures, while far away from Alaska both traits decreased with increasing air temperatures. In spring, northern wheatears increasingly exploited flow assistance with season, which is likely a behavioural adjustment to speed up migration by increasing the distance travelled per night. Furthermore, the variation in total stopover duration but not in travel speed had a significant effect on the total speed of migration, indicating the prime importance of total stopover duration in the overall phenology of bird migration. Conclusion Northern wheatears from Alaska provide evidence that the phenotypic reaction norm to a set of environmental conditions cannot be generalized to universal and persistent behavioural reaction pattern across entire migratory pathways. This highlights the importance of full annual-cycle studies on migratory birds to better understand their response to the environment. Understanding the mechanisms behind phenotypic plasticity during migration is particularly important in the assessment of whether birds can keep pace with the potentially increasing phenological mismatches observed on the breeding grounds

Timing is crucial for consequences of migratory connectivity

Migratory connectivity can have important consequences for individuals, populations and communities. We argue that most consequences not only depend on which sites are used but importantly also on when these are used and suggest that the timing of migration is characterised by synchrony, phenology, and consistency. We illustrate the importance of these aspects of timing for shaping the consequences of migratory connectivity on individual fitness, population dynamics, gene flow and community dynamics using examples from throughout the animal kingdom. Exemplarily for one specific process that is shaped by migratory connectivity and the timing of migration – the transmission of parasites and the dynamics of diseases – we underpin our arguments with a dynamic epidemiological network model of a migratory population. Here, we quantitatively demonstrate that variations in migration phenology and synchrony yield disease dynamics that significantly differ from a time‐neglecting case. Extending the original definition of migratory connectivity into a spatio‐temporal concept can importantly contribute to understanding the links migratory animals make across the globe and the consequences these may have both for the dynamics of their populations and the communities they visit throughout their journeys

Defining the Degree of Seasonality and its Significance for Future Research

Seasonality describes cyclic and largely predictable fluctuations in the environment. Such variations in day length, temperature, rainfall, and resource availability are ubiquitous and can exert strong selection pressure on organisms to adapt to seasonal environments. However, seasonal variations exhibit large scale geographical divergences caused by a whole suite of factors such as solar radiation, ocean currents, extent of continents, and topography. Realizing these contributions in driving patterns of overall seasonality may help advance our understanding of the kinds of evolutionary adaptations we should expect at a global scale. Here, we introduce a new concept and provide the data describing the overall degree of seasonality, based on its two major components—amplitude and predictability. Using global terrestrial datasets on temperature, precipitation and primary productivity, we show that these important seasonal factors exhibit strong differences in their spatial patterns with notable asymmetries between the southern and the northern hemisphere. Furthermore, our analysis reveals that seasonality is highly diverse across latitudes as well as longitudinal gradients. This indicates that using a direct measure of seasonality and its components, amplitude and predictability, may yield a better understanding of how organisms are adapted to seasonal environments and provide support for predictions on the consequences of rapid environmental change

Tracking the full annual-cycle of the Great Knot, Calidris tenuirostris, a long-distance migratory shorebird of the East Asian-Australasian Flyway

The Great Knot Calidris tenuirostris is one of the iconic long-distance migratory species of the East Asian-Australasian Flyway. However, despite extensive flagging and banding efforts, very little is known about the migratory strategies and the breeding grounds of this species that spends the non-breeding season mainly on the northern shorelines of Australia. Using light-level geolocators deployed on Great Knots at Roebuck Bay (Western Australia), we describe the individual migration strategies, breeding locations and breeding-related behaviour. Based on data from eight successfully tracked individuals, we found that all except one migrated to the western part of the known breeding range. This was 2,000–2,500 km from the eighth individual that commenced breeding in the potentially sep- arated eastern part of the range. Light intensity and temperature profiles provided evidence that four of the birds successfully hatched chicks. Of the three which failed, one appeared to have laid a second clutch before failing again. Arrival at the breeding grounds and the laying of eggs were remarkably synchronous between individuals, as were the arrival dates back at Roebuck Bay. Departure from the breeding grounds was more spread out, partly dependent on breeding success and also as a result of females probably leaving the nesting area before males. The individual migration strategies confirmed the strong dependence of this species on the Yellow Sea as their major stopover site during both southward and northward migration. Furthermore, all individuals stopped at least once on their northward journey to the Yellow Sea from Australia. And in reverse, all individuals stopped at least once on the southward migration before arriving at the Yellow Sea coming from their Arctic breeding grounds. The results indicate that this species will most likely be further affected by the rapid habitat loss in the area of the Yellow Sea and other parts of the Chinese coastline

First breeding record of the light-mantled sooty albatross (Phoebetria palpebrata) for the maritime Antarctic

The light-mantled sooty albatross is a medium-sized albatross with a circumpolar distribution in the Southern Ocean. The known breeding sites are restricted to Islands in sub-Antarctic latitudes close to the Antarctic convergence between 46° and 53°S. In the austral summer season 2008/2009 we discovered a new breeding colony with at least two confirmed and three probable nests at Fildes Peninsula, King George Island, South Shetland Islands, Antarctica (62°12′S, 59°01′W). The new breeding colony of light-mantled sooty albatross described here represents the southernmost breeding place of any albatross species ever recorded

The adequacy of aging techniques in vertebrates for rapid estimation of population mortality rates from age distributions

As a key parameter in population dynamics, mortality rates are frequently estimated using mark–recapture data, which requires extensive, long‐term data sets. As a potential rapid alternative, we can measure variables correlated to age, allowing the compilation of population age distributions, from which mortality rates can be derived. However, most studies employing such techniques have ignored their inherent inaccuracy and have thereby failed to provide reliable mortality estimates. In this study, we present a general statistical model linking birth rate, mortality rate, and population age distributions. We next assessed the reliability and data needs (i.e., sample size) for estimating mortality rate of eight different aging techniques. The results revealed that for half of the aging techniques, correlations with age varied considerably, translating into highly variable accuracies when used to estimate mortality rate from age distributions. Telomere length is generally not sufficiently correlated to age to provide reliable mortality rate estimates. DNA methylation, signal‐joint T‐cell recombination excision circle (sjTREC), and racemization are generally more promising techniques to ultimately estimate mortality rate, if a sufficiently high sample size is available. Otolith ring counts, otolithometry, and age‐length keys in fish, and skeletochronology in reptiles, mammals, and amphibians, outperformed all other aging techniques and generated relatively accurate mortality rate estimation with a sample size that can be feasibly obtained. Provided the method chosen is minimizing and estimating the error in age estimation, it is possible to accurately estimate mortality rates from age distributions. The method therewith has the potential to estimate a critical, population dynamic parameter to inform conservation efforts within a limited time frame as opposed to mark–recapture analyses

First tracks of individual Blackcaps suggest a complex migration pattern

The Blackcap Sylvia atricapilla is a model species for the evolution of bird migration in a time of global change. However, many assumptions about putative changes to their migratory paths have not been verified because, until recently, it has not been possible to track individual small passerines throughout the entire migration cycle. With the recent development of miniaturised light-level geolocators, it is now possible to track passerines throughout the migration cycle and test these latter assumptions. We deployed 100 geolocators on Blackcaps breeding in southern Germany in 2015, and recaptured three of these birds in 2016. We used a new analytical tool implemented in the R package GeoLight to identify stopover sites during migration. One bird migrated due west to winter in southern England or possibly northwestern France, whereas two birds migrated south towards North Africa via Italy. Although none of the retrieved geolocators collected data throughout the entire migration cycle, the data suggest that migration patterns of the species are more complex than previously thought

First insights into the migration route and migratory connectivity of the Paddyfield Warbler using geolocator tagging and stable isotope analysis

The Paddyfield Warbler Acrocephalus agricola has recently expanded its breeding range westwards to the western coast of the Black Sea. Although its non-breeding range is known (southern Iran to northern Myanmar), current knowledge on how individual birds migrate and how their routes evolve alongside range expansion processes is very limited. Data from one geolocator deployed on a Paddyfield Warbler at a recently established breeding site in Bulgaria show that this individual retraced the recent range expansion and followed a rather conservative route instead of migrating directly to India. An additional stable hydrogen (δ2H) analysis of feathers from 25 individual breeding birds in Bulgaria that had been grown during their stay in the non-breeding grounds indicated a low degree of migratory connectivity at the non-breeding grounds. Our results provide a first insight into the migration pattern of the Paddyfield Warbler and should stimulate further research on the use of the understudied Indo-European flyway by this species

Consistent variation in individual migration strategies of brown skuas

Seabirds show remarkable variability in migration strategies among individuals and populations. In this study, we analysed 47 migrations of 28 brown skuas Catharacta antarctica lonnbergi breeding on King George Island in the Maritime Antarctic. Brown skuas from this population used a large area during the non-breeding period north of 55°S, including parts of the Patagonian Shelf, Argentine Basin and South Brazil Shelf, areas which are characterised by high levels of marine productivity. However, individual birds utilised only a subset of these areas, adopting 1 of 4 distinct migration strategies to which they were highly faithful between years, and showed high repeatability in departure and arrival dates at the breeding ground. Although they spent the majority of the non-breeding season within a particular region, almost all individuals used the same area in the late winter, exploiting its seasonal peak in productivity. Overall, these results indicate consistent individual variation in migration strategies that may reflect a combination of genetic control and individual experience, but with considerable flexibility to shift distribution in response to prevailing environmental conditions