There are concerns that waders nesting in open landscapes are threatened by habitat fragmentation, and may be increasingly so in the future by a drive to plant more trees. Plantations obviously remove nesting space used by species such as Lapwing and Ringed Plover but they could also create hiding places for predators that can then target nests in the vicinity. In a 2022 paper in Animal Conservation, Triin Kaasiku and colleagues report on the outcomes of 753 Estonian wader nests in open areas close to forest edges along Estonia’s coastal fringe. Which are the key predators and where do they hunt?
Open landscapes have been lost at an unprecedented rate over the past century. Warmer temperatures and reduced management of semi-natural landscapes provide ideal circumstances for the establishment of shrub growth and the expansion of forests. At the same time, afforestation campaigns are encouraging tree planting, to generate revenue and perhaps contribute to climate change mitigations. The combined effects of these drivers are exacerbated by the way that these processes increase the fragmentation of these already-threatened open habitats, which have traditionally provided homes for waders such as Dunlin and Curlew.
Waders in Estonia
The semi-natural wet pastures of the Baltic coast have persisted for centuries, formed by the combined effects of floods, winter ice and postglacial land uplift, and through grazing by domestic livestock and wild geese. Together, these processes have created and preserved important wader breeding habitat. Sixty years ago, Estonia’s coastal grasslands used to be full of Lapwing, Dunlin and Redshank, as well as Black-tailed Godwit, Curlew, Common Snipe and Ruff. Since then, farmland abandonment and afforestation, both as a result of commercial forestry and natural succession, have reduced the area of coastal grasslands by about 70%.
The Boreal Baltic coastal grassland habitat is listed as a priority habitat type in Annex I of the EU Habitats Directive. Despite efforts to restore this habitat, by reducing reed and tree cover over the last two decades, most wader populations in these areas have not recovered. This is discussed in a blog about the effectiveness of agri-environment schemes in the same study area (Remote monitoring of wader habitats). Direct habitat loss is part of the problem for Estonia’s breeding waders but increased predation rates may also be a factor. Triin Kaasiku and colleagues have studied this diverse breeding wader community, to learn more about how nest predation varies across this wet grassland-forest system.
Follow that nest
Wader breeding densities at the study sites varied from 7 to 160 wader pairs per km2; the upper end is considered to be a high density, at the European level. Nests were found and then revisited approximately weekly. The Animal Conservation paper describes fully how evidence was used to determine whether nests were successful and to consider the probable causes of failures. Wader nest survival was measured during three breeding seasons (2018-2020).
Lapwing, Ringed Plover, Redshank and Dunlin were the four main species studied by Triin Kaasiku and her colleagues (see table). They accounted for 655 out of the 753 nests, with six other species providing smaller samples. To understand more about predation events, the team deployed camera traps alongside 85 of the nests, all of which were within 1 km of trees and forests.
About 80% of nesting attempts were unsuccessful (526 out of 655) and the outcomes of 14 other nests could not be established. Of the known failures, 89% were lost to predation, while other causes of nest failures included abandonment (6.7%), flooding (2.3%), trampling (0.2%), and others where the causes were unclear (2.3%). The seemingly high nest abandonment rate may also include some nests that were subject to temporary flooding. The results are based on 679 nests that either hatched or where there was evidence of predation.
There were no discernible differences in survival rates for different species. This is in line with findings in an Icelandic study that compared outcomes of open-nesting species (Golden Plover, Oystercatcher and Whimbrel) with those of species that hide their nests (Redshank, Black-tailed Godwit and Snipe). See Where to nest?
DSR is higher further from the forest and where the amount of cover is lower. These two metrics are obviously related but the effects are teased apart in the paper.
From the modelled data, a nest that is only 20 m from forest edge has a 7% chance of being successful (95% CI = 5-11%), while the equivalent figure for one that is 1 km away is about 26% (18-34%).
Similarly, 3% (1-8%) of nests hatch when local forest cover (within 1 km of the nest) is about 50%, compared to 19% (15-23%) in completely open areas.
Predators and predation
Nest cameras were deployed to track what happened to 85 nesting attempts. Although 64 nests were predated, the camera trap only managed to record the nest predator in 41 cases. Of these events, 31 nests were lost to Red Fox, 5 to Golden Jackal, 3 to Raven and 2 to Badger.
Fox predation occurred on average at 217 m (95% CI=161-273 m) from the forest edge but the other mammals tended to predate nests that were further from cover. Predation events by Raven may also be more frequent closer to forest edge, but these events were rare. Based on the recordings of the camera traps, Red Fox detection rate was higher closer to the forest edge but no similar relationship was found with the proportion of forest cover.
In this Estonian study, wader nest survival did not vary with distance from smaller patches of trees or bushes (<30 m wide). Perhaps these patches may be too small for Red Foxes to hide or forage in.
The bigger picture
There is strong evidence, from studies in the UK and elsewhere, that species that breed in open habitats avoid woodland (see the WaderTales blog Mastering Lapwing conservation) and may experience greater population declines in more fragmented landscapes (as discussed in Curlews can’t wait for a treatment plan).
In the Estonian wet grassland-forestry patchworks studied by Triin Kaasiku and colleagues, Red Fox was the most commonly encountered predator operating close to forest edge. It was in these areas that eggs were most likely to be taken. This is in line with some other studies – but by no means all. The authors discuss in detail why different guilds of predators may have different effects in different circumstances and how patterns might be distorted if waders actively avoid nesting near forests or if there are complex predator-prey networks. See Further Reading below.
Hatching success is not high in any of the areas studied in Estonia – even at the lowest forest cover, only 19% of the nests hatch. This result shows that habitat fragmentation may have more severe effects on the open landscape species than previously realised. It may also indicate that more attention should be directed at the high number of generalist predators.
In Estonia, as elsewhere, landowners are being encouraged to use land to grow food, to deliver biodiversity gain and to lock up carbon. Others can argue whether planting trees is necessarily a good thing for carbon capture, especially if deep peat is drained and cultivated in the process, but forestry is becoming more fashionable. This paper reminds us that piece-meal planning decisions that, for instance, provide grants to one landowner to preserve habitat for declining species of wader and grants for a neighbour to plant trees, are unlikely to maximise biodiversity benefits.
The full paper is available here:
Predation-mediated edge effects reduce survival of wader nests at a wet grassland-forest edge. Triin Kaasiku, Riinu Rannap and Peep Männil. Animal Conservation. doi.org/10.1111/acv.12774
Foxes play leading roles in several WaderTales blogs but this selection may be of particular interest:
Tool-kit for wader conservation looks at different ways of reducing predation, particularly by foxes, within lowland wet grassland. The focus is upon issues in the UK.
Can habitat management rescue Lapwing populations? assesses whether the available tools have the power to deliver sustainable wader populations.
Trees predators and breeding waders is a cautionary tale. Reestablishing nesting habitat for species such as Dunlin and Curlew is not just a matter of removing the trees. It may take up to ten years for predator numbers to drop to levels that are associated with an open landscape.
Dunlin: tales from the Baltic is not focused on predation but fragmentation and predation are parts of the story. Veli-Matti Pakanen’s Finnish research is complementary to the studies in Estonia.
WaderTales blogs are written by Graham Appleton (@GrahamFAppleton) to celebrate waders and wader research. Many of the articles are based on published papers, with the aim of making shorebird science available to a broader audience.