Ruth Dunn shares insights on her latest study where, alongside her colleagues, she investigated the number of marine birds, outside of their breeding seasons, that may be undetectable when underwater during at-sea surveys.
Investing in renewable energy developments, as opposed to burning fossil fuels, has been hailed as a route through which humans might be able to counteract anthropogenic-induced climate change.
Within western Europe, it is now commonplace to look out over the countryside, or out to sea, and be greeted with the sight of huge white turbines. These otherworldly structures are seen by many as beacons of hope that can help us to harness the earth’s natural resources, rather than diminish those that are limited.
Interactions between renewable energy developments and nature
As governments increasingly invest in renewable energy technologies, it is important to ensure that developments are implemented in a way that is as considerate of the natural world as possible.
Research into the interactions between renewable energy developments and the wildlife that they ultimately seek to safeguard has therefore sparked a multitude of questions:
- How long after the construction of a windfarm does it take for displaced raptors to return?
- How do bird flight heights impact their vulnerability to turbine strikes?
- What ecological communities are supported by the artificial reefs that form around the foundations of wind turbines?
- How might the noises produced during the construction and operation of renewable energy developments impact wildlife?
A key step towards answering these questions involves understanding just how many individual animals might be affected by renewable energy developments. Calculating this, as with many ecological questions, is often all the more challenging when the focus is the marine realm. Even counts from boats and planes have their limitations when your species of interest (be it a cetacean or a marine bird) dives below the water’s surface and out of sight.
Estimating marine bird numbers
Within our study, we sought to estimate how many birds might be underwater and out of sight during these at-sea surveys, so that values from surveys can be adjusted and more probable estimates obtained.
Although values that correct for marine birds being underwater and out of sight are sometimes currently used, they are often derived from data collected at particular times and in specific locations. The amount of time that marine birds spend underwater, however, can differ depending on where they are, and may also vary throughout the course of the annual cycle. For example, during the summer, marine birds need to feed their chicks as well as themselves. Contrastingly, during the winter, they might have to spend more time foraging underwater to counterbalance the energetic costs of thermoregulation.
Collecting new data
Within our study, we harnessed dive data collected from miniaturised depth recorder loggers that were placed around the legs of Atlantic puffins, common guillemots, red-throated divers and razorbills at breeding sites within western Europe. We deployed these small bio-logging devices during the birds’ breeding seasons and then returned the following year to retrieve them and download their data.
As well as providing lots of new ecological information about the diving behaviour of these birds outside their breeding seasons, the data also allowed us to estimate the number of birds that might be missed during surveys.
There was a lot of variation in the time that the birds spent underwater, this varying by species, month, and location.
This variation is not currently captured when estimating the number of marine birds within key areas that are signposted for both current and future renewable energy developments.
For example, it is not currently common practice to correct for red-throated divers being underwater and current estimates of their non-breeding abundances are therefore likely to be underestimates that in some cases miss almost a third of the population.
What should we do?
Within our paper we provide updated values that will enable counts of Atlantic puffins, common guillemots, red-throated divers and razorbills within western Europe to be corrected for so that we can better consider just how many birds might be impacted by offshore renewable energy developments.
We hope that our study paves the way for the use of other bio-logging datasets from other species and in other locations to help us to more accurately count different populations of marine birds.
Ultimately, as part of our quest to divest from fossil fuels and instead harness the earth’s natural resources, we should also try to formulate the most accurate understanding possible of the animals and ecosystems that renewable energy developments are likely to affect.
Read the full article ‘Temporal and spatial variability in availability bias has consequences for marine bird abundance estimates during the non-breeding season’ in Ecological Solutions and Evidence.
