Assessing the potential impact of additional mortality from anthropogenic causes on animal populations requires detailed demographic information. However, these data are frequently lacking, making simple algorithms, which require little data, appealing. Because of their simplicity, these algorithms often rely on implicit assumptions, some of which may be quite restrictive. Potential Biological Removal (PBR) is a simple harvest model that estimates the number of additional mortalities that a population can theoretically sustain without causing population extinction. However, PBR relies on a number of implicit assumptions, particularly around density dependence and population trajectory that limit its applicability in many situations. Among several uses, it has been widely employed in Europe in Environmental Impact Assessments (EIA), to examine the acceptability of potential effects of offshore wind farms on marine bird populations. As a case study, we use PBR to estimate the number of additional mortalities that a population with characteristics typical of a seabird population can theoretically sustain. We incorporated this level of additional mortality within Leslie matrix models to test assumptions within the PBR algorithm about density dependence and current population trajectory. Our analyses suggest that the PBR algorithm identifies levels of mortality which cause population declines for most population trajectories and forms of population regulation. Consequently, we recommend that practitioners do not use PBR in an EIA context for offshore wind energy developments. Rather than using simple algorithms that rely on potentially invalid implicit assumptions, we recommend use of Leslie matrix models for assessing the impact of additional mortality on a population, enabling the user to explicitly define assumptions and test their importance.

Protected sites for birds are typically designated based on the site’s importance for the species that use it. For example, sites may be selected as Special Protection Areas (under the European Union Directive on the Conservation of Wild Birds) if they support more than 1% of a given national or international population of a species or an assemblage of over 20,000 waterbirds or seabirds. However, through the impacts of changing climates, habitat loss and invasive species, the way species use sites may change. As populations increase, abundance at existing sites may go up or new sites may be colonized. Similarly, as populations decrease, abundance at occupied sites may go down, or some sites may be abandoned. Determining how bird populations are spread across protected sites, and how changes in populations may affect this, is essential to making sure that they remain protected in the future. These findings come from a new study by Verónica Méndez and colleagues from the University of East Anglia working with BTO. Using Wetland Bird Survey (WeBS) data the study looked at changes in the population sizes and distributions of 19 waterbird species across Britain during a period of 26 years and their effect on local abundance and site occupancy. Some of these species saw steady increases in population size (up to 1,600%, Avocet), whereas other saw mild declines (-26%, Purple Sandpiper and Shelduck). The results showed that changes in total population size were predominantly reflected in changes in local abundance, rather than through the addition or loss of sites. This is possibly because waterbirds tend to be long-lived birds, with high site fidelity and new suitable sites may not always be available. Thus colonisation of new sites may typically occur when their existing sites approach their maximum capacity. As changes in populations are largely manifested by changes in local abundance – and as sites are often designated for many species – the numbers of sites qualifying for site designation are unlikely to be affected. Understanding the dynamic between population change and change in local abundance will be key to ensuring the efficiency of protected area management and ensuring that populations are adequately protected. Data from the Wetland Bird Survey and its predecessor schemes, which are celebrating 70 years of continuous monitoring of waterbirds this year, have been integral to both the designation of protected sites and monitoring of their condition. Continuation of this monitoring through future generations will ensure that the impacts to waterbird populations of future environmental changes may be understood.

In a changing world, the development of green energy is more important than ever. One of the most well-developed and cheaply available options is wind power, but there is evidence that wind farms can also have a negative impact on biodiversity. This 2017 study, funded by the Cambridge Conservation Initiative and led by BTO, is the first to look at the global impact of wind farms on bird and bat populations. Although the most obvious threat from wind turbines is that of collisions, as birds fly into the turbine, the threats from wind farms are not solely collision-based. They also have the potential to displace species from their nesting or feeding areas, restrict movements, or destroy key habitats used by different species. The study reviewed 234 papers which look at both bat and bird collision rates with wind farms. These were then examined in relation to several of the factors that may play a role in collisions, including the physiological and behavioural traits of individual species, and the height and energy output of turbines. The results show that birds using ‘artificial habitats’ (e.g. farmland or urban areas) run a higher risk of colliding with wind turbines than birds living elsewhere, although this could be due to the fact that many wind farms are located within such habitats. Perhaps unsurprisingly, migratory birds faced a greater risk than sedentary ones; similarly, species of bat which dispersed further, on average, had a higher risk of collision than those that didn’t. Out of the 362 bird species examined, 55 were considered as being ‘threatened’ by wind farms. Thirty-one of these were birds of prey, species that are generally slow to reproduce and which are more sensitive to the impact of losing breeding adults to wind turbines. Collision rates in general were predicted to be higher for bats than for birds, emphasising their vulnerability to wind farms. Individually, larger turbines were associated with a higher collision rate than small turbines, but wind farms comprising a large number of smaller turbines resulted in the highest rates of collision. In practical terms this suggests that using a few large turbines may lower collision rates for birds, although it is worth noting that turbines with a capacity of more than 1.25 MW were linked to high collision rates for bats. Given the growing demands for green energy, it is essential that we consider the impacts of wind farms on populations of both bats and birds, especially migrants and wide-ranging species. Taking into account knowledge of the birds and bats using an area when considering the placement of wind farms and individual turbines (e.g. by avoiding migratory flyways) could greatly reduce the risk of collisions. The work also underlines a need for more research to be carried out in emerging economies and in relation to offshore wind farms, both of which are areas where valuable information is currently lacking. This will surely help to find the delicate balance between a greener future and healthy biodiversity.

Wader populations are declining worldwide, with causes often being linked to the loss and degradation of habitats, increased predation, and a changing climate. Here in the UK, we have seen dramatic declines in Curlew populations over recent decades, resulting in the species being proposed as the UK’s most important bird conservation priority. If we are to halt and reverse these declines then we first need to understand which threats this iconic species is facing.

The UK has lost seven species of breeding birds in the last 200 years. Conservation efforts to prevent this from happening to other species, both in the UK and around the world, are guided by species’ priorities lists, which are often informed by data on range, population size and the degree of decline or increase in numbers. These are the sorts of data that BTO collects through its core surveys. For most taxonomic groups the priority list is provided by the International Union for Conservation of Nature (IUCN) – the IUCN Red List comprises roughly 12,000 species worldwide and their conservation status. However, for birds in the UK, most policy makers refer to the Birds of Conservation Concern (BoCC) list, updated every six years (most recently in 2015). A new study funded by the RSPB and Natural England in cooperation with BTO, WWT, JNCC, and Game & Wildlife Trust has carried out the first IUCN assessment for birds in Great Britain. The study applied the IUCN criteria to existing bird population data obtained from datasets like the BTO/JNCC/RSPB Breeding Bird Survey (BBS). The criteria take into account various factors, most notably any reduction in the size (both in abundance and range) of populations, loss of habitats key to the species, small or vulnerable population sizes, and extinction risk. Alongside this, the criteria look to see if there is a “rescue” effect – such as immigration from neighbouring populations that might boost the population’s numbers, reducing the risk of extinction. The species are then categorised into one of the threat levels below. The results of the new study show that a concerning 43% of regularly occurring species in Great Britain are classed as Threatened, with another 10% classified as Near Threatened. Twenty-three breeding or non-breeding populations of birds were classed as Critically Endangered, including Fieldfare and Golden Oriole (both possibly extinct as breeders), Whimbrel, Turtle Dove, Arctic Skua and Kittiwake, as well as non-breeding populations of Bewick’s Swan, White-fronted Goose and Smew., Over the past 200 years, seven species have gone extinct as breeders in Britain, including Serin, Temminck’s Stint and Wryneck in the past 25 years. The total percentage of threatened birds in Great Britain (43%) is high compared to that seen elsewhere in Europe (13%). Reasons for this are not entirely clear, although it may be that Britain’s island status has something to do with this, as there are fewer neighbouring “rescue” populations. Although the results from the IUCN assessment and BoCC assessment largely overlap, the IUCN assessment raises the level of concern for species such as Red-Breasted Merganser, Great Crested Grebe, Moorhen, Red-Billed Chough (all classed as Vulnerable), and Greenfinch (Endangered). These species might thus warrant closer monitoring in the near future. In contrast, the BoCC assessment identifies a number of species of concern whose declines have been more gradual but over long time periods (e.g. Skylark and House Sparrow). The authors emphasise that this assessment is not a replacement of the BoCC report, but rather that the two reports complement each other. With this new wealth of knowledge, there will hopefully be even more support for those species that need it most.

1. Individual-based models (IBMs) are a powerful tool in predicting the consequences of environmental change on animal populations and supporting evidence-based decision making for conservation planning. 2. There are increasing proposals for wind farms in UK waters and seabirds are a vulnerable group, which may be at risk from these developments. 3. We developed a spatially explicit IBM to investigate the potential impacts of the installation of wind farms in the English Channel and North Sea on body mass, productivity and mortality of a breeding population of Northern gannets for which we have tracking data. 4. A baseline model with no wind farms accurately represented the status of a sample of tracked gannets at the end of the 90-day chick-rearing period, and the behaviourtime budget was similar to that of tracked gannets. 5. Model simulations in the presence of wind farms indicated that installations should have little impact on the gannet population, when either avoidance behaviour or collision risk scenarios were simulated. Furthermore, wind farms would need to be ten times larger or in more highly used areas in order to have population-level impacts on Alderney’s gannets. 6. Synthesis and applications. Our spatially explicit individual-based models (IBM) highlight that it is vital to know the colony-specific foraging grounds of seabirds that may be impacted, when identifying potential wind farm sites, in order to account for cumulative impacts from multiple sites. Avoiding areas highly used for foraging and commuting, and avoiding large-scale developments should be effective in limiting gannet mortality as a result of collision, competition and energy expenditure. Our IBM provides a robust approach which can be adapted for other seabird populations or to predict the impacts from other types of spatial change in the marine environment. 1. Individual-based models (IBMs) are a powerful tool in predicting the consequences of environmental change on animal populations and supporting evidence-based decision making for conservation planning. 2. There are increasing proposals for wind farms in UK waters and seabirds are a vulnerable group, which may be at risk from these developments. 3. We developed a spatially explicit IBM to investigate the potential impacts of the installation of wind farms in the English Channel and North Sea on body mass, productivity and mortality of a breeding population of Northern gannets for which we have tracking data. 4. A baseline model with no wind farms accurately represented the status of a sample of tracked gannets at the end of the 90-day chick-rearing period, and the behaviourtime budget was similar to that of tracked gannets. 5. Model simulations in the presence of wind farms indicated that installations should have little impact on the gannet population, when either avoidance behaviour or collision risk scenarios were simulated. Furthermore, wind farms would need to be ten times larger or in more highly used areas in order to have population-level impacts on Alderney’s gannets. 6. Synthesis and applications. Our spatially explicit individual-based models (IBM) highlight that it is vital to know the colony-specific foraging grounds of seabirds that may be impacted, when identifying potential wind farm sites, in order to account for cumulative impacts from multiple sites. Avoiding areas highly used for foraging and commuting, and avoiding large-scale developments should be effective in limiting gannet mortality as a result of collision, competition and energy expenditure. Our IBM provides a robust approach which can be adapted for other seabird populations or to predict the impacts from other types of spatial change in the marine environment.