Seasonal bait uptake by individual grey squirrels measured by PIT-tags and Rhodamine B

Oral contraceptives are being developed to manage the impacts of the grey squirrel. To be effective, contraceptives will need to be deployed at a landscape scale and will require a delivery system that is practical and economically viable. Understanding grey squirrel feeding behaviour is important so that delivery methods can be designed to ensure enough target individuals receive an effective contraceptive dose at a time of year that will ensure they will remain infertile throughout peak times of breeding. The main aims of this study were to assess how sex, season, squirrel density and bait point density influenced; 1) the probability of a squirrel visiting a feeder and 2) the amount of bait consumed from feeders. Field trials were conducted on six woodland populations of squirrels in three seasons, with four days of bait deployment via purpose-designed squirrel-specific bait hoppers with integrated PIT-tag readers., Trials were conducted in five independent woods that were located at least 3.5 km apart and within 25 km of York, England (53.96oN, -1.09oE; Figure 1). Populations of grey squirrels were sampled from woods HW and SC in winter 2017/2018, woods SC and PW in summer 2022 and woods GE and BW in spring 2023. Autumn was not trialed due to reduced squirrel breeding activity and high natural food availability, which could potentially deter squirrels from using feeders. To provide two suitable replicates for each season, woods were selected that were of a similar size (between 7 and 8 ha) and structure (mature broadleaf or mature broadleaf conifer mixed tree species), that had high levels of grey squirrel activity reported by landowners and established squirrel populations, with minimal squirrel control conducted within the previous 12 months. At the end of each trial, the squirrel population was trapped and removed from each wood as part of other related studies. Therefore, wood could not be re-..., , # Seasonal bait uptake by individual grey squirrels measured by PIT-tags and Rhodamine B

[https://doi.org/10.5061/dryad.m905qfvb0](https://doi.org/10.5061/dryad.m905qfvb0)

### **Description of the data and file structure**

The purpose of this study was to measure factors affecting individual bait uptake by grey squirrels (*Sciurus carolinensis*), to inform the future delivery of an oral contraceptive. The Excel file contains PIT-tag data from grey squirrels trapped in six independent UK woodlands between 2017 and 2023. 202 grey squirrels were anaesthised, PIT-tagged and released in 2 woods in winter 2017/2018, 2 woods in summer 2022 and 2 woods in spring 2023. Bait hoppers with integrated PIT-tag readers were deployed evenly across each wood on wooden stands and baited for up to 2 weeks (density 2/ha or 3/ha) and feeding visits and amount of bait per visit were recorded for 4 to 8 days. For 4 to 8 days the bait was hazelnut paste containing 0.18% Rhodamine B bait marker. When consum...