FIGURE 2.

Female tree swallows supplemented with calcium showed increased telomere shortening as indicated by female telomere shortening adjusted for regression to the mean for calcium (blue; n = 22) versus control nests (yellow; n = 26). Older female tree swallows also showed increased telomere shortening as indicated by female telomere shortening adjusted to regression to the mean for 1‐year‐old (n =29) and older than 1‐year‐old birds (n =19). Adjustments for regression to the mean scales the mean of the data to zero.