Data from: Early to rise, early to breed: a role for daily rhythms in seasonal reproduction

Vertebrates use environmental cues to time reproduction to optimal breeding conditions. Numerous laboratory studies have revealed that light experienced during a critical window of the circadian (daily) rhythm can influence reproductive physiology. However, whether these relationships observed in captivity hold true under natural conditions and how they relate to observed variation in timing of reproductive output remains largely unexplored. Here we test the hypothesis that individual variation in daily timing recorded in nature (i.e. chronotype) is linked with variation in timing of breeding. To address this hypothesis and its generality across species, we recorded incubation behavior data to identify individual patterns in daily onset of activity for 2 temperate-breeding songbird species, the dark-eyed junco (Junco hyemalis aikeni) and the great tit (Parus major). We found that females who first departed from their nest earlier in the morning (earlier chronotype) also initiated nests earlier in the year. Date of data collection and ambient temperature had no effect, but stage of incubation influenced daily onset of activity in great tits. Our findings suggest a role for daily rhythms as one mechanism underlying the observed variation in seasonal timing of breeding.Data File KeyContains descriptors of column headers for both .csv files.DataFileKeyBehavEcol.txtGreat Tit Data File for RGreat Tit (Parus major) data file used for statistical analysis in R Statistical Software.GreatTitRData.csvJunco Data File for RDark-eyed Junco (Junco hyemalis) data file used for statistical analysis in R Statistical Software.JuncoRData.csvR Code for Behavioral Ecology MSR code used with provided .csv files for both species. Includes all models used in the MS.BehavEcolRCode.RFunding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: IRFP-0852986, IOS-125752