Milestone reached for WWT Curlew headstarting project

An exciting milestone has been reached this year for the Wildfowl and Wetlands Trust (WWT) Curlew headstarting project, with the confirmation that a bird released in 2019 has bred successfully in the Severn and Avon Vales for the first time.

The bird was one of fifty released at the WWT Slimbridge reserve in July and August 2019 after eggs were rescued from nests on military airbases in the east of England, where they would have been destroyed, under licence, to protect air safety. They were transported to WWT Slimbridge, where they were raised by the Trust’s avicultural experts before being released into the wild, a technique known as headstarting.

Headstarting can be utilised as part of wider conservation efforts to provide a short-term boost to a wild population by ensuring a high proportion of young fledge. Even in healthy populations, only a small proportion of chicks will survive to fledge. Protecting them during this vulnerable stage and releasing them into the wild once they can take flight boosts the number of fledglings produced by a population. It is hoped that these young birds will then return to breed once they have matured, which for Curlew is from their second year onwards.

In 2019, each headstarted Curlew was fitted with a yellow ring on the right tibia and a white alphanumeric ring on the left tibia, with an engraved number between 21 and 70, always reading up (see Figure 1).

Figure 1. Photograph of headstarted Curlew 68 on the Severn estuary showing the colour mark scheme used in 2019 – a yellow ring on the right tibia and a white alphanumeric ring on the left tibia. Photo © John Sanders

The WWT Severn Curlew Project received news in June that a pair of Curlew were showing potential breeding behaviour at a site in the south of the Severn and Avon Vales study area (SAV) and on further investigation were confirmed to be rearing a single chick (see Figure 2). The good news got even better when one of the adults was seen to be carrying yellow and white rings, indicative of a headstarted bird from the 2019 cohort. A concerted effort to read the ring confirmed that the bird was male 23, a headstarted individual, setting up the prospect of a successful breeding attempt by a headstarted bird in the SAV study area for the first time, in the first viable year since their release.

Figure 2. Photograph of male 23 keeping a close eye on his chick in a recently cut hay meadow. Photo © WWT

Over the following weeks the birds were monitored regularly (with permission from the landowners) and the chick was fitted with a coloured leg flag and rings which form part of a new colour marking scheme. The chick has a yellow ring on its right tibia (the scheme marker), a yellow two digit alphanumeric flag on its left tibia engraved ‘00’ (enabling it to be individually identified), above a smaller yellow ring which identifies it as a wild ringed chick (see Figure 3). The adult female had departed for the coast by 8 July (breeding females normally depart early, leaving the male to watch over the chick until fledging) and the chick was seen flying on 12 July with male 23 still in attendance on the breeding site. However, the following day a report came in from local birder Peter Hazelwood that he had seen male 23 back at Oldbury power station on the Severn estuary, where it had been seen regularly during the 2020/21 winter. A check of the breeding site later that day failed to locate the fledgling which we are confident has fledged successfully and we now wait in anticipation for a sighting of the juvenile on a wintering site somewhere in south west England or further afield.

The headstarted Curlew in this story, male 23, has been resighted thirty-seven times since being released on 12 July 2019. After spending its first month post release on the WWT Slimbridge reserve, the bird moved ten miles downriver where it was seen at regular intervals at high tide roosts by local ring reader John Sanders and local birder Peter Hazelwood (who often observed the bird on his patch at Oldbury power station) between September 2019 and early April 2021. The bird was seen on the estuary on 4 April but then not seen again until it was located at the SAV breeding site in June, before taking up residence back on the estuary on 13 July.

Figure 3. Photograph of the Curlew chick showing the colour flag and ring combination that identifies it as a wild ringed chick. The flag bears the inscription ‘00’ (zero zero) enabling it to be individually identified. Photo © Mervyn Greening

Author: David Evans (WWT Severn Curlew Officer)

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