Variation in foraging tactics and diet are usually attributed to differences in morphology, experience, and prey availability. Recently, consistent individual differences in behaviour (personality) have been shown to be associated with foraging strategies. Bolder or more exploratory individuals are predicted to have a faster pace-of-life and offset the costs of moving more or in risky areas, with higher energetic gains by encountering profitable foraging opportunities and prey. However, the relationship between personality, foraging, and diet is poorly understood.

We investigated how exploratory behaviour in red knots (Calidris canutus) is associated with foraging tactics and diet by combining laboratory experiments, field observations, and stable isotope analysis. First, we developed a mobile experimental arena to measure exploration speed in controlled settings. We validated the method by repeated testing of individuals over time and contexts. This setup allowed us to measure exploratory personality at the field site, eliminating the need to bring birds into captivity for long periods of time. After releasing birds within days of their capture, we asked whether exploration speed was associated with differences in foraging tactics and diet in the wild.

We found that tactile foraging red knots mainly caught hard-shelled prey that are buried in the sediment, whereas visual foraging knots only captured soft preys located close to or on the surface. We also found that faster explorers showed a higher percentage of visual foraging than slower explorers. By contrast, morphology (bill length and gizzard size) had no significant effect on foraging tactics. Diet analysis based on δ15N and δ13C stable isotope values of plasma and red blood cells confirmed our field observations with slower explorers mainly consumed hard-shelled prey while faster explorers consumed more soft than hard-shelled prey.

Our results show that foraging tactics and diet are associated with a personality trait, independent of morphological differences. We discuss how consistent behaviour might develop early in life through positive feedbacks between foraging tactics, prey type, and foraging efficiency.

Isotope data: Red blood cell and plasma d13C and d15N isotopes collected from the blood samples of red knots.

Exploration speed: Movement tracjectories were collected from the recordings of the top camera during experiments in the mobile arena. We used the distance between estimated positions to calculate speed. Errors in the positioning algorithm were filtered by excluding speeds higher than 200 cm/s. An individual’s exploration speed was calculated as the average speed during each 20 min trial. The dataset includes four repeats of exploration speed.

Proportion of explorative behaviour: Behaviours were collected from the recording of the side camera during experiments in indoor arena and mobile arena. Behavioural budget is calculated of the time that the focal bird spend exploring (walking and probing) the arena. 

Foraging behaviour: Foraging behaviour was collected from the observations in the field. Focal birds were filmed for 20 min or up to the moment they flew away. Behavioural budget is calculated for two types of foraging tactics: ‘tactile foraging’ when a bird is probing continuously with the bill into the substrate, and ‘visual foraging’ when a bird is scanning the area in front of it and pecking at items seen on the substrate surface. 

Prey-foraging behaviour: In cases that we could identify the ingested prey in the field, categorized as hard-shelled prey (e.g., cockles or Baltic tellins) or soft prey (e.g., brown shrimp or polychaete worms) to investigate the relationship between foraging tactics and diet.

GENERAL INFORMATION

1. Titles of the Dataset: Exploration speed (mean speed cm/sec) in mobile arena, exploration behaviour (behavioural budget walking and probing), isotope data (plasma and red blood cell), foraging behaviour collected from the observations in the field
2. Date of the data collection: Catching between 14 August - 19 September 2018, and 1 August - 6 September 2019, Field observations from August to October 2019
3. Geographic location of data collection: Western Dutch Wadden Sea (53°15'N, 5°15'E) 
4. Corresponding author information: Selin Ersoy, NIOZ Royal Netherlands Institute for Sea Research, Department of Coastal Systems, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands, selin.ersoy@gmail.com 
5. Link to publication: Ersoy et al. (2021) Exploration speed in captivity predicts foraging tactics and diet in free-living red knots. Journal of Animal Ecology

DATA & FILE OVERVIEW

DATA & FILE OVERVIEW
1. KnotData.csv: Metadata of individual red knots
         Column 1: CaptureDate: The date when the red knots were captured by means of mist-netting in the Western Duthc Wadden Sea (53°15'N, 5°15'E)
         Column 2: RingNr: Unique metal ring number of red knots. Ring were put on the legs
         Column 3: Crc: Unique combination of color-rings of red knots. Rings were placed on the legs (two in right and two in left legs)
         Column 4: Bill: Bill lenght of the individual in mm.
         Column 5: Mass: Body mass of the individual in gr.
         Column 6: cell_d15N: Isotope value from red blood cell d15N. 
         Column 7: cell_d13C: Isotope value from red blood cell d13C. 
         Column 8: plasma_d15N: Isotope value from blood plasma d15N. 
         Column 9: plasma_d13C: Isotope value from blood plasma d13C. 
         Column 10: Expl_F01_MeanSpeed: Exploratory personality score of individual measured in mobile arena for the first time (mean speed cm/sec)
         Column 11: Expl_F01_Log10MeanSpeed: Log10 transformed of the exploratory personality score of individual measured in mobile arena for the first time (mean speed cm/sec)
         Column 12: Expl_Date: The date that exploratory personality assay was conducted

2. ExplorationSpeedRepeatibility.csv: Data on repeated measurement (max. 4 repeats) on exploration speed (mean speed log10 cm/sec) measured in the mobile arena
         Column 1: RingNr: Unique metal ring number of red knots. Ring were put on the legs 
         Column 2: MeanSpeed: Exploratory personality score of individual measured in mobile arena (mean speed cm/sec)
         Column 3: Expl_Date: The date that exploratory personality assay was conducted
         Column 4: Condition: Whether the individual bird was wildly captured or it was in captivity
         Column 5: Repeat_Nu: Repeat number of the personality assay trials

3. ExplorationValidation.cvs: Data on personality measurements on both mobile (FU) and indoor (WU) arenas. Exploration is scored both mean speed and behavioural budget as proportion of walking and probing
         Column 1: RingNr: Unique metal ring number of red knots. Ring were put on the legs 
         Column 2: Expl_Date: The date that exploratory personality assay was conducted
         Column 3: Setup: Whether the personality was measured in mobile (FU) or indoor (WU) arenas.
         Column 4: Condition: Whether the individual bird was wildly captured or it was in captivity
         Column 5: PropExplBehaviour: Exploratory personality scored as behavioural budget as proportion of walking and probing
         Column 6: Mean_Expl_Speed: Exploratory personality scored as movement speed

4. ForagingFieldData.csv: Data on proportion of foraging tactics (tactile and visual) observed in the field. 
         Column 1: RingNr: Unique metal ring number of red knots. Ring were put on the legs 
         Column 2: Expl_F01_MeanSpeed: Exploratory personality score of individual measured in mobile arena for the first time (mean speed cm/sec)
         Column 3: gizzard_size: Gizzard size of the individual red knots measured through ultrasound (following Dekinga et al., 2001)
         Column 4: bill_length: Bill lenght of the individual in mm.
         Column 5: p_visual: Proportion of visual foraging observed in the field
         Column 6: p_tactile: Proportion of tactile foraging observed in the field

5. PreyForagingBehv.csv: Data on which foraging tactic (tactile and visual) result in catching what type of prey (soft and hard-shelled) observed in the field.
         Column 1: Obs_id: Field observation id. Combination of colour ring combination (crc) and the date of observation.
         Column 2: totalingested_prey: Number of total ingested prey observed from that observation
         Column 3: prey_type: Identified type of prey (shellfish, worm, shrimp, cockle)
         Column 4: Foraging: What types of foraging behaviour was observed during that ingestion (tactile vs visual)
         Column 5: Prey: Whether that prey type is hard-shelled or soft prey