Behavioral observations (home environment condition)

Under the home environment condition (in the barn and in the range), one experimenter observed the behavior of 58 randomly selected individuals, among the 117 identified chickens, over three different periods: from day 14 to day 19 (period 1, before range access), from day 37 to day 46 (period 2, first weeks of range access), and from day 63 to day 72 (period 3, last weeks of range access).

To prevent any impact of the observer's presence and the noises linked to the stopwatch, the observer spent 3 h at least per day in the barn with the chicks for their 7 first days of life.

Due to time constraints, observation days were continuous over period 1, while for periods 2 and 3, the observations were executed 3 days per week, spaced of 1 or 2 days. Each observation day started between 8:00 and 9:30 in the morning and ended by 17:00.

Behavioral data were collected using the continuous sampling method, and each focal animal was observed for 30 s, four times a day. As days shortened over time, observations within the same day were spaced from 3 h (period 1) to 1 h and a half (periods 2 and 3).

The behaviors were divided into states and events. States were all behaviors lasting more than 1 s, and events those lasting less than 1 s. The events were recorded in 'all occurrences', meaning that every event behavior was counted within the 30 s of each focal animal. The observer recorded the duration of the state behaviors using a stopwatch and the number of occurrences of the event behaviors. The full ethogram is described in Table ​Table11.

Ethogram of recorded behaviors.

ATOL_0000837 (lying)

ATOL_0000816 (immobility)

ATOL_0000844 (investigative behavior trait)

ATOL_0000845 (physical investigation)

ATOL_0002158 (ingestion)

ATOL_0000363 (feeding behavior trait)

ATOL_0000361 (drinking behavior trait)

Include two behaviors:

 Feeding: Feeds at the feed containers in the barn

 Drinking: Drinks at the water containers in the barn

ATOL_0000902 (agonistic behavior)

ATOL_0000813 (aggressive behavior)

ATOL_0000653 (comfort behavior trait)

ATOL_0000822 (auto-body care trait)

ATOL_0000823 (preening)

ATOL_0000360 (body scratching)

Include five behaviors:

 Shaking: Ruffles the feathers and shakes the body

 Stretching: Stretches wing or leg

 Tail wagging: Wiggles its tail horizontally or vertically

 Wing flapping: Flaps its extended wings in a vertical plane

 Preening: Grooms its plumage with the beak in a sitting, lying, or standing position

ATOL_0000846 (conspecific investigation)

ATOL_0000817 (approach response trait)

ATOL_0000826 (allo-body care trait)

^aThese behaviors were rare (less than 5% of the observed individuals expressed the behavior) and were discarded from statistical analyses.

^bTraits in reference to the ontology ATOL: https://www.atol-ontology.com/en/atol-2/.

Individuals had their behavior recorded over 16 days (6 days in period 1 and 5 days for period 2 and period 3), resulting in 32 min of observation per chicken.