Eggs and Chicks - by Patrick Laurie
Working for Waders’ Patrick Laurie looks at the challenges of springtime, and why many wading birds find it so hard to breed and produce new young successfully in the modern Scottish countryside.
We know that waders are doing badly because they’re unable to rear enough chicks each year. That much is understood from a number of scientific studies, and it points to the fact that predation and disturbance during the breeding season are key drivers of decline. Most waders sit on their eggs for almost a month before they hatch, and then there’s a period of between four and six weeks when chicks are out-and-about, but unable to fly or look after themselves. It’s a challenging period for the birds, and we’re still working hard to understand how a number of different factors have come together to create a “perfect storm”
Given a chance, waders are incredibly resilient and careful parents. They know exactly what’s right for their eggs and chicks, and the level of care they provide to their young is exceptional. But nesting and chick-rearing throw up a number of problems which change as the process advances.
In many ways, a breeding attempt is at its most vulnerable during the incubation period. The eggs are laid on the ground, and their main defence is an extraordinary level of camouflage. Wader eggs are famously hard to find, but that can work against the birds if the nests are made in fields where farmers are working. It’s difficult to see a wader’s nest from a tractor, and while many farmers love waders and do an enormous amount to conserve the birds, lots of eggs are probably damaged or lost during agricultural operations. Given that eggs can’t move themselves out of harm’s way, they’re also vulnerable to flooding during periods of wet weather. This can be devastating, and it can be a leading cause of nest failure in some parts of Scotland.
Adult waders are noisy and protective parents, and they will defend eggs with vigour and enthusiasm if predators appear. However, eggs are frequently found and eaten by a worryingly long list of birds and mammals, including badgers, foxes, hedgehogs, rats, stoats, crows, ravens, rooks, jackdaws and weasels. Many of these species would kill an adult wader if the opportunity presented itself, so the parent birds are only really able to complain or mimic a violent defence. A full-on attack would be too dangerous for them.
The longer a nest has been incubated, the more committed the adult birds become to protecting it. In terms of disturbance by human beings or dog-walkers, a wader that is disturbed from its nest within a day or two of laying eggs could easily fly away and not come back. As the eggs get closer to hatching, the adult bird is far more likely to return – but repeated disturbance can be very stressful and it may draw predators into the area.
It might sound like the incubation stage is full of potential problems, but just as many issues arise once the eggs have hatched. Aside from flooding, eggs are pretty weather-proof during the incubation period. However, as soon as the chicks hatch, they’re vulnerable to extended periods of cold, wet weather. Tint chicks are easily chilled to death, and bad rain in the first few weeks after hatching can be disastrous.
Eggs are vulnerable because they can’t move, but in some ways that is a good thing. As soon as chicks hatch, they move around all over the place. Adult birds can find it hard to keep tabs on their young, and there’s always a risk that they might fall into ditches or holes and drown or starve to death. Eggs are vulnerable, but at least they stay where you put them. For wader conservationists, it’s easy to protect a nest of eggs from farming operations like ploughing or grass cutting - but once they’ve hatched, it can be very difficult to find chicks in order to protect them. As the tractors or machines approach, they’re often hard-wired to clap down and hide, making it even harder to help them.
The list of predators is also likely to change when chicks hatch out of their eggs. Badgers, hedgehogs and rats are likely to stumble upon eggs and eat them all in one sitting, but it would probably be unusual for them to hunt chicks and eat them one-by-one. At the same time, birds of prey like buzzards and red kites show no interest in eating eggs, but they are happy to kill chicks, even when they’re almost fully-fledged. Foxes are a fairly constant threat throughout the entire breeding process – they’re as keen on eggs as chicks and adult birds.
That’s another important point about the breeding season – it’s not just the chicks which fail during the important spring months. Adult birds are often killed too, particularly by foxes and raptors and in collisions with fences and overhead wires. It’s a stressful time, and even if they don’t succeed in hatching chicks, there’s a risk that they’ll be killed themselves.
The situation is grave, and many of these issues are made worse by changes in land use, particularly the loss of habitat to forestry and intensification of grassland management. Speaking about the issue of predation and poor productivity in breeding waders, ecologist David Jarrett said “Predation is a natural process and waders have evolved alongside our common predator species. However, various human influences over habitats and landscapes have tipped the balance heavily in the favour of predators, to the extent that few chicks would fledge each year without interventions like predator fencing or lethal control.”
The picture is extremely complicated and it will depend upon a wide range of variables which change from place to place. There’s also an enormous variety of complexities which vary between wader species - at anything more than a very general level, it’s hard to compare the experience of a redshank with that of a curlew. We need to gather more information on productivity, but we also need to support practical land management which places an emphasis on predator management alongside habitat creation measures.