The Curlew breeding season is in full swing at RSPB Insh Marshes. We catch up with our Curlew LIFE intern Martine Stead to see how it’s going so far…
“Now it is all about searching for chicks,” urges Thijs Claes, Curlew LIFE project officer, over a chilli he’s cooked for the Curlew LIFE volunteers and staff at RSPB Insh Marshes on Friday 12 May.
Searching for chicks! It was hard enough finding adults sitting on nests – we’re even more dubious about our ability to spot balls of fluff lower than an adult Curlew’s knee. However, we do begin to pick up some clues. We notice that curlew parents sometimes behave differently to non-parents. Instead of preening or napping or engaging in prolonged bouts of feeding, they’re permanently watchful. They pace steadily, 20 or so metres from the other parent, and look repeatedly left to right – like teachers escorting a primary school group across a busy road, counting heads and chiding stragglers to keep together.
The first time I see chicks, after an hour of watching, I’m thrilled to finally spot two small fluffy heads bumbling between the vegetation. They walk like toddlers in wellies, with exaggerated and determined steps. Sometimes you see the vegetation move before the chick appears. Sometimes you watch for ages, occasionally seeing just the one chick, then all of a sudden 3 or 4 appear and you realise they were there all along, just hidden in a wee ditch or behind the grass. At this time of year, the vegetation grows quicker than the chicks – good for them, less helpful for us.
Before the chicks started appearing, it was all about monitoring the eggs and attempting to trap the adults for ringing and tagging. Alex Starace, Senior Research Assistant, needed to get to each nest to measure the length, width and weight of the eggs. These figures in combination help to predict the hatching date. (Eggs become less dense over time as carbon dioxide and water vapor are diffused through the shell). When a nest is within a week of hatching, this is the best time to try to trap the adult, because it will be particularly reluctant to leave the eggs for very long. Adults are caught with the aid of a nest trap, a soft net ‘cage’ with one entrance.
Tricks & traps
Together with Thijs, or conservation officer Sarah West, Alex approaches each nest and then places the cage over the nest. The two of them then retreat out of sight and wait until the adult returns, hoping that it will walk in through the entrance of the cage and resume sitting on the eggs. Some do, some don’t. If the bird doesn’t want to enter, the cage is removed and the nest left in peace. If the bird does enter it, the researchers walk out there as quickly as possible to gently remove the bird and carry out ringing and tagging.
One quirky aspect of this process is the role played by dummy eggs. You obviously don’t want the real eggs to get damaged, so they are put safely in an insulated box during the trapping, and fake eggs left in their place. These eggs have to look convincing enough, at least for a few minutes, to assure the parent that the nest hasn’t been harmed. I spent an enjoyable few days making new fakes out of some left-over clay in the RSPB workshop and my birthday set of acrylic paints.
Back to the chicks. This year the team use radio-tagging of chicks for the first time. It will allow us to determine fledgling success rates and gain a better understanding of how chicks use the different habitats on the reserve, ultimately helping us to boost the local Curlew population. The tagging involves trapping the chicks while they are still on the nest – within a day or two of hatching – and attaching a small radio tracker with antenna to the down on the chick’s back.
We can then use a radio receiver to detect each chick’s unique frequency, which should aid with location and identification. It doesn’t turn out to be quite so straightforward, as we often have nests in the same area of the marshes, meaning that we could be picking up signals from one set of chicks but seeing a different set of chicks. The receiver isn’t able to pinpoint location that accurately from a distance. Also, some of the tags fall off or are removed from the chicks, but carry on emitting signals afterwards. Nevertheless, other tags remain in place, and the data is still potentially useful. For example, the tags can potentially provide clues as to which predator took a chick, based on tag location, damage marks on the tags or DNA testing.
Sometimes there are wonderful moments: on one occasion I accompanied Alex on his walk out to a nest to check progress. We were greeted by two extremely new arrivals: one chick was a few hours old, and one chick was still damp from emerging from the shell even more recently. The other two eggs were ‘holed’ – showing signs of the inhabitants beginning to chip away at the shell with their egg-tooth.
The chicks were placed in a yoghurt pot to be weighed on the little scales. They have ridiculously large feet and tiny wing stumps, which they flex curiously. On the birthday of Adrian, assistant warden at RSPB Insh Marshes and half-time on the Curlew LIFE project, we spotted a whole new brood of chicks in an area where we hadn’t previously seen a nest. A special birthday present.
Sometimes, chick searching is less uplifting. I was sent out on the marshes on one occasion to check on a nest approaching its hatching date, and was excited at the prospect of seeing some egg-holing, or even a newly hatched chick. But only a single fragment of egg shell remained on the nest. Later scanning of the camera images revealed that the culprit was a nocturnal badger who appeared to have chomped its way through all the eggs over the course of an hour.
Predators on camera
Other predators picked up by our cameras include a stoat, fox and carrion crows. The cameras also indicate trampling by ponies and deer, and disturbance by sheep. Despite these hazards, we know by the end of May that two thirds of our known nests have hatched – a good rate. For the Curlew population to remain stable, around 0.5 chicks per breeding pair (or roughly one in eight) needs to survive each year. In order to better understand the predation pressures and other factors associated with nest failure and survival in different areas of the reserve, we need to thoroughly monitor all the nests and chicks until the surviving chicks fledge in July and August.
Video: © RSPB Thijs Claes
Each extra day of survival moves the chicks closer towards ‘teenager’ stage, when the body profile transforms from chunky to upright, and the little bill starts to extend and then curve downwards. I feel emotionally invested in three or four broods in particular – among them the nest that I found, the eggs that I helped to measure).
“Two chicks sighted at Gordonhall with adult,” someone reports on the group chat, stating the time and grid reference. That’s one of ‘mine’, I think, and give a little inward cheer.
Martine Stead, 5 June 2023