Saving Nests Is the Easy Part of Curlew Recovery
Updated: Sep 10
Quick summary
Twenty-eight recovery projects reported large gains in Curlew nest success after fencing and predator control.
Chick survival stayed very low after intervention in almost every project reviewed.
BTO modelling suggests 1.06 chicks hatched per breeding pair for stability — a different measure from 0.6 fledged.
A modelled loss of favourable management cut population growth from 18.3% to 8.0% a year.
Twenty-eight Curlew recovery projects across the UK and western Europe were asked what their work had achieved. Most could show more nests hatching. Almost none could show more chicks surviving.
That split features throughout BTO Research Report 797, published as part of the Curlew Solutions Trial and funded through Natural England's Species Recovery Programme.
Projects reported uplifts in nest success once nests were fenced or foxes and crows were controlled, often with very large effect sizes. Chick survival barely changed. As many projects recorded more chick predation after intervention as recorded less.
The stability figure, and why it looks unfamiliar
BTO modelling suggests that around 1.06 chicks hatched per breeding pair per year may be sufficient to hold the UK population steady, compared with a current estimate of around 1.00.
Anyone who has followed Curlew conservation will have met a much lower number: roughly 0.6 fledged chicks per pair. Both figures are in the report, and they do not contradict each other. They count different things.
Fledged chicks per pair counts chicks that survive to flying age. The thresholds usually quoted are 0.63 (Taylor et al. 2020) and 0.68 (Viana et al. 2023) fledged chicks per pair, or 0.43 fledged chicks per nest (Cook et al. 2021).
Hatched chicks per breeding pair counts chicks that leave the egg. Survival from hatching onwards is then handled separately in the model, inside the rate for young birds reaching one year old.
BTO switched metric deliberately. Curlew chicks leave the nest within hours, range up to a kilometre and hide in tall vegetation, so counting fledglings takes licences, tags and staff time, and the resulting rates are not comparable between projects.
Counting hatched chicks is something most projects can already do reliably. The report states plainly that its 1.06 figure is not directly comparable with the older fledging thresholds.
The same modelling gives the alternative route to stability. If hatching rates stayed flat, survival from hatching to one year old would instead need to rise from roughly 30% to 34%. The authors judge that scale of increase achievable, given the nest success gains some projects have already delivered.
What projects are actually doing
Nest fencing and lethal control of mammalian predators were each used by more than three-quarters of projects. Most fenced individual nests at 20 x 20m or 25 x 25m.
Equipment ran to between £500 and £1,000 per nest, with one project putting staff time at around £2,500 a year, and only a few projects had any of that met through agri-environment schemes.
Several relied on local farmers or shoots to carry out fox and crow control rather than doing it in-house, which is worth remembering when the cost of these schemes is totted up.
Two practical findings stand out. First, doing more did not mean achieving more: some of the largest uplifts in nest success came from projects running only one or two intervention types.
Second, one project recorded two nests abandoned immediately after fencing went in, which staff put down to an eight-person installation team, bad weather arriving, and an unusually dense electric fence.
The numbers behind the model
The population model uses 510 nest records submitted to the BTO Nest Record Scheme between 1980 and 2018, plus skipping and re-nesting rates taken from 20 GPS-tagged birds in North Wales.
The authors say so plainly, and add that models built on national averages cannot be assumed to hold at local scale. Most respondents were working in grassland rather than heather moor.
The growth rates below are outputs of that model, not measurements from the field. The report describes them as thought experiments: each one asks what would happen to population growth if a package of interventions shifted nest success and chick survival by a given amount. They are useful for comparing the direction and scale of change between scenarios, not as forecasts for any particular moor.
Three starting conditions were tested:
Low productivity ground, worked hard, still declined. High-intensity intervention moved it from 7.3% loss a year to 2.3% loss a year.
Medium productivity ground turned around. A 1.3% annual decline became growth of 4.2%, or 13.2% at higher intensity.
High productivity ground produced 18.3% growth a year. The nest success and chick survival rates behind that scenario were taken from Baines et al.'s 2023 study of farmland bordering land used for grouse shooting and under intensive predator control.
Model that management being withdrawn, through less predator control or through tree planting, and growth falls from 18.3% to 8.0%. The report is clear that this scenario is largely hypothetical: Curlews are known to decline in abundance when favourable management stops, but nobody has measured the direct effect on nest success or chick survival in waders.
Effort needed follows the same pattern. Stabilising the UK population would take interventions at around 17% of nest attempts, or around 5% where those interventions are intensive.
In Wales, where the Breeding Bird Survey records a 40% fall in ten years, it would take 52% of all nests, or 22% at high intensity.
Where this leaves the uplands
The best-performing land in the model is farmland next to shooting estates, where someone else is already paying for the predator control.
Calladine and colleagues found that 36% of Britain's breeding Curlews nest on ground that overlaps grouse moors. The report's most striking scenario is what the model does when that management is taken away: half the projected growth disappears with it. The threats it lists are tree-planting targets in Protected Landscapes, the switch to Environmental Land Management, and farmers moving from hay to silage.
The model also estimates that around 22% of Curlew chicks die within two days of hatching, while chicks range up to 1 km, usually less than 500m, before fledging. Field-scale measures may therefore reach birds that nest-level fencing cannot, though the report is clear this is untested.
What the report will not tell Defra is who pays. Its conclusion is that recovery is possible only with sufficient funding, and the ground already producing Curlew chicks is being kept in that condition by people whom no scheme currently pays.
Why this matters
The cheapest Curlew conservation in the country is the management already happening on and around managed moorland, and the modelling shows how much is lost if it stops.
