Biology subjects

Wanless, S.

Publications and source records attributed to Wanless, S..

5 recordsLinked to original sources

bioRxiv2026

AN UPDATED POPULATION ESTIMATE FOR NORTHERN GANNETS ACROSS THEIR NORTH-EAST ATLANTIC BREEDING RANGE FOLLOWING THE 2022 OUTBREAK OF HIGH PATHOGENICITY AVIAN INFLUENZA

Northern gannets (Morus bassanus) have been regarded as a seabird success story, due to population increases throughout the 20th and 21st century contrasting with global seabird declines. However, in 2022 gannets experienced a severe outbreak of High Pathogenicity Avian Influenza (HPAI) across their global distribution, leading to an urgent need to reassess their population status. This study presents breeding gannet census numbers for 2023/24 from all colonies across the North-East Atlantic metapopulation (Great Britain, Ireland, the Channel Islands, Iceland, Norway, the Faroe Islands, France, Germany, Russia). Gannet numbers decreased by 17% across the North-East Atlantic metapopulation between the 2013/14 and 2023/24 census from 414,598 to 345,854 apparently occupied sites (AOS), a global decrease of at least 13%. The bulk of the reduction in AOS was driven by the largest colonies (>10,000 AOS) each losing tens of thousands of AOS. These figures likely underestimate the impact of the HPAI outbreak worldwide, since most colonies will have increased between the last census in 2013/14 and the 2022 HPAI outbreak, and the Canadian breeding population was last counted pre-HPAI outbreak. Scotland still holds the largest proportion of both the North-East Atlantic metapopulation (59%), and the world population (46%), while Great Britain, Ireland and the Channel Islands together hold 83% of the North-East Atlantic metapopulation and 64% of the world population. This study not only presents an updated population census for gannets in the North-East Atlantic but illustrates the large-scale impacts of a disease outbreak on a seabird species across its global range and highlights the importance of more regular census efforts to better quantify the demographic consequences of such events.

ecology↗

bioRxiv2026

Flight crashes have demographic consequences in a long-lived seabird

Risk is a key currency in animal ecology, yet studies of risk have almost exclusively focused on predation. Accidents, defined as a momentary loss of control, represent another potential source of injury and mortality. Such events are seldom documented and are generally assumed to be vanishingly rare in natural systems. Nonetheless, regular crash-based mortality has been documented in a population of northern gannets through monthly surveys conducted over three years in the 1970s. We revisit these data, using hindcasting, environmental records and computational fluid dynamics (CFD) models to investigate the environmental drivers of gannet crashes, and matrix population models to examine their demographic consequences under a range of environmental scenarios. Wind direction emerged as the sole predictor of crash-based mortality, with the probability of crashes increasing in north-westerly winds. CFD models revealed that north-westerlies are associated with a marked increase in turbulent kinetic energy along the breeding cliffs, relative to the other modal wind direction, which likely challenges flight control. A total of 367 crashes accounted for 5.4% of annual adult mortality. Removing this mortality led to a projected increase in population of 23.9% over 50 years, equivalent to an additional 10,583 individuals. Overall, this suggests that turbulence close to the substrate can result in fatal losses of flight control that can impact population-level processes. Our results also highlight the need for greater understanding of how airflows influence the risk of accidents across flying animals, both in current and changing wind regimes.

zoology↗

bioRxiv2025

Changing food conditions and size declines in a North Sea forage fish

Declining body sizes are prevalent in marine fish. While these declines have been suggested to be a response to increasing temperatures, the evidence is mixed and the underlying causes of observed declines often unknown. Here, we explore drivers of spatio-temporal patterns in size in lesser sandeel (Ammodytes marinus), an important prey for seabirds and marine mammals, focusing on ongoing size declines in the North Sea. We combine experimental and field data with ecological theory to develop a biologically realistic dynamic energy budget model that explicitly models feeding, metabolism and energy allocation to produce daily predictions of size during the juvenile growth season from 1979 to 2016. When forced with daily temperature estimates and zooplankton data from the Continuous Plankton Recorder, model predictions reproduce observed spatio-temporal patterns in size well. Our results suggest that the most plausible driver of observed size declines in the western North Sea is declining prey densities. In contrast, the direct effect of temperature on sandeel size is small, but interacts with local prey availability so that the effect varies in both size and direction over space. Our results thus suggest that to understand effects of climate change on fish size we need to account for both direct physiological effects and changes in resource availability. Finally, we use the model to show that early-life phenology and turbidity (via its impact on intake rates in the visually foraging sandeel) may also impact sandeel size, highlighting the importance of broadening our view of potential drivers of size declines.

ecology↗

bioRxiv2023

Strong breeding colony fidelity in northern gannets following High Pathogenicity Avian Influenza Virus (HPAIV) outbreak

High pathogenicity avian influenza virus (HPAIV) caused the worst seabird mass-mortalities on record in Europe across 2021-2022. The northern gannet (Morus bassanus) was one of the most affected species, with tens of thousands of casualties in the northeast Atlantic between April-September 2022. Disease outbreaks can drastically modify the movement ecology of animals and diminish spatial consistency, thereby increasing the potential for disease transmission. To detect potential changes in movement behaviour, we GPS-tracked breeding adults following the initial HPAIV outbreak, at three of the largest gannet breeding colonies where major mortality of adults and chicks occurred (Bass Rock, Scotland, UK; Grassholm, Wales, UK; Rouzic island, Brittany, France). Crucially, GPS-tracked birds remained faithful to their breeding sites and did not prospect other breeding colonies. They performed regular foraging trips at sea, similar to their behaviour before the outbreak. Gannet foraging effort was nonetheless lower than in 2019, thus surviving birds may have benefited from reduced intra- and interspecific food competition. Breeding colony fidelity of adult northern gannets following HPAIV mass-mortalities suggests limited long-term capacity to virus spread, which may contrast with the behaviour of adults during the disease outbreak, or with that of younger individuals.

ecology↗

bioRxiv2022

Components of micro-evolutionary and phenotypic change in seasonal migration versus residence in a wild population

Dissecting joint micro-evolutionary and plastic responses to environmental perturbations fundamentally requires quantifying interacting components of genetic and environmental variation underlying expression of key traits. This ambition is particularly challenging for phenotypically discrete traits where multiscale decompositions are required to handle non-linear transformations of underlying genetic and environmental variation into phenotypic variation, especially when effects have to be estimated from incomplete field observations. We devised a novel joint multistate capture-recapture and quantitative genetic animal model, and fitted this model to full-annual-cycle resighting data from partially migratory European shags (Gulosus aristotelis) to estimate key components of genetic, environmental and phenotypic variance in the ecologically critical discrete trait of seasonal migration versus residence. We demonstrate non-trivial additive genetic variance in latent liability for migration, resulting in estimated micro-evolutionary responses following two episodes of strong survival selection. Yet, underlying additive genetic effects interacted with substantial permanent individual and temporary environmental effects to generate complex non-additive effects, causing large intrinsic gene-by-environment interaction variance in phenotypic expression. Our findings reveal how temporal dynamics of seasonal migration result from combinations of instantaneous micro-evolution and within-individual phenotypic inertia, and highlight how plastic phenotypic variation could expose cryptic genetic variation underlying discrete traits to complex forms of selection.

evolutionary biology↗