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Temporal trend at the population level in (A) mean laying date (Julian days) of tree swallows, (B) spring temperature (°C) and (C) density of breeders (% of occupied nest boxes) over the 40 farms monitored between 2004 and 2013. Black circles depict mean values (±SE) over all farms for each year, and black lines are model predictions (dotted lines: 95% CI).
