Data from: Using molecular and crowd-sourcing methods to assess breeding ground diet of a migratory brood parasite of conservation concern

Breeding ground food availability is critical to the survival and
productivity of adult birds. The common cuckoo Cuculus canorus is a
brood-parasitic Afro-Palearctic migrant bird exhibiting long-term
(breeding) population declines in many European countries. Variation in
population trend between regions and habitats suggests breeding ground
drivers such as adult food supply. However, cuckoo diet has not been
studied in detail since before the most significant population declines in
Europe began in the mid-1980s. 20th century studies of cuckoo diet largely
comprised field observations likely to carry bias towards larger prey
taxa. Here we demonstrate the potential value of 1) using high-throughput
DNA sequencing of invertebrate prey in faeces to determine cuckoo diet
with minimal bias towards large prey taxa, and 2) using crowd-sourced
digital photographs from across Britain to identify lepidopteran cuckoo
prey taxa during recent years post-decline (2005-2016). DNA analysis found
a high frequency of Lepidoptera, including moths of family Lasiocampidae,
prominent within the past literature, but also grasshoppers (Orthoptera)
and flies (Diptera) that may be overlooked by field observation
methodologies. The range of larval lepidopteran prey identified from
photographs largely agreed with those previously documented, with
potential signs of reduced diversity, and identities of key adult prey
taxa were supported by molecular results. Notably, many identified cuckoo
prey taxa have shown severe declines due to agricultural intensification,
suggesting this has driven spatial patterns of cuckoo loss.
Landscape-scale, lowland rewilding interventions provide opportunities to
understand the scale of reversal of previous agricultural intensification
that may be necessary to restore prey populations sufficiently to permit
recolonization by cuckoos.