Population assessment and foraging ecology of the rare solitary bee Anthophora retusa at Seaford Head Nature reserve

Anthophora retusa is a rare solitary bee which has declined throughout Britain and other European countries since the 1990s. It is thought to be restricted to five sites in Britain. However, information on these remaining populations is limited. Knowledge on population size, habitat and forage requirements and foraging distance, are important for successful conservation of species. The population of A. retusa at the Seaford Head Nature reserve in East Sussex was surveyed. Transects within the reserve were conducted and population estimates using mark recapture were made for 2018 and 2019. Pollen from foraging females was analysed alongside visual sightings to determine forage requirements. The total population was estimated to be 91 in 2018 (males and females) with an estimated male population of 167 in 2019. The most visited flower species by females was Glechoma hederacea (66% of visits) but flower preference changed throughout the flight season, shifting to Fabaceae species and Iris foetidissima with 16 plant groups identified in pollen samples. Bees were geographically restricted to a small area within the reserve (approximately 30 ha). Although the exact location of nesting sites was not determined with certainty it is thought nests are in the loess deposits at the top of the inaccessible sea cliff face. This project suggests the presence of appropriate nesting sites may be limiting A. retusa distribution as they appear to forage on common plant species. More research is needed on the exact nesting requirements of the species. The findings from this paper help contribute to the limited understanding of the ecology of this rare and declining species. By knowing the forage requirements of A. retusa, other areas where it is found can ensure these are present within a short distance of nest sites, hopefully ensuring the survival of individual populations and therefore the species.