Breeding Twite survive only in fragmented remnants of their former distribution in England, with the species suffering an ongoing decline and considered of high conservation concern in the UK.
Climate change and agricultural intensification have been blamed for the decline but the exact driving factors have not been identified. Across the UK, Twite declined by 21% between 1999 and 2013, while the South Pennine population has fallen by 72% over the same period and it is thought that just 30 breeding pairs may have survived there in 2021.
Along with north-west Derbyshire, where a similar crash appears to be taking place, the South Pennines form the core breeding range in England.
Each Twite trapped was fitted with three colour-rings to enable individuals to be identified without having to catch them again (Jack Bucknall).
A study led by Ismini Gkourtshouli-Antonsiadou of Imperial College London has investigated Twite survival rates in north-west Derbyshire through an intensive ringing study. The team was keen to learn whether there were any differences in survival between young birds and adults in order to inform conservation efforts.
Breeding Twite in an area of sheep-grazed pasture and limestone quarries near Doves Hole were monitored between 2016 and 2020. A total of 258 Twite were trapped, the majority aged as young or adult by moult characteristics, then fitted with a coded combination of three colour-rings at a feeding station. This was followed up by logging sightings of ringed birds at the station on alternate days between March and October in order to measure survival.
Data modelling allowed apparent survival rates of 0.14-0.31 for first-year Twite and 0.28-0.51 for adults to be estimated, showing that young birds suffered higher mortality with less than a third surviving their first year, even at the optimistic end of the calculations.
The survival demonstrated for adult Twite is similar to Common Linnet and European Goldfinch, though survival of juveniles is poorer compared to these species, perhaps due to winter food availability, suggesting this may be a driver of the decline in Twite. However, the researchers could not draw a firm conclusion due to the considerable variation in survival of both age classes over the study period.
The team also pointed out that they did not monitor breeding productivity as part of the study, so could not eliminate the possibility that poor productivity has led to the decline of the Derbyshire population. Most of the nesting birds in the study area are subject to disturbance in a working quarry, as well as potential pressure from predation and food availability.
Increasing food availability during the non-breeding period was recommended as a trial intervention to complement existing conservation measures such as improving habitat conditions and increasing seed sources in the summer.
Gkourtsouli-Antoniadou, I, et al. 2023. Age-specific survival in an English Twite Linaria flavirostris population. Bird Study. DOI: https://doi.org/10.1080/00063657.2023.2166459