DOI: 10.5061/dryad.q2bvq83kt
title: Data from: The birth hour of mammals: insights from intra-specific variation in wild blue monkeys

description: While most mammals show birth hour peaks at times of the 24-hour cycle
 when they are less active, there are exceptions to this general pattern.
 Such exceptions have been little explored, but may clarify evolutionary
 reasons for the diel timing of births. We investigated intraspecific
 variation in birth hour in wild blue monkeys (Cercopithecus mitis
 stuhlmanni), a diurnal primate, to identify factors that differentiated
 daytime vs. nighttime births. Behavioral and life history data from 14
 groups over 14 years revealed that 4% of 484 births occurred during the
 day. Probability of daytime birth varied with mother’s age,
 peaking at 15.7 years. Births whose annual timing deviated most from the
 population’s peak birth months were five times more likely to occur during
 daytime than those that deviated less. There was no evidence that mother’s
 rank or infant sex influenced birth hour, and mixed evidence that daytime
 births were more probable in larger groups. Survivorship did not differ
 significantly for infants born during the day vs. night. Prime-aged
 mothers may be able to handle the consequences of an unusual birth hour
 more successfully than mothers with less experience or those weakened by
 age. Daytime birth may be more advantageous in the off-season because
 nights are colder at that time of year. These findings are consistent with
 hypotheses relating birth hour to the risk of losing social protection in
 group-living animals, but are not consistent with those emphasizing risk
 of conspecific harassment. Patterns of within-species variation can help
 in evaluating evolutionary hypotheses for non-random birth hour.
description: Data were collected from January 2006 through March 2020 via
 field observations of wild, individually-recognized blue monkeys living in
 multiple groups in the Kakamega Forest, Kenya. Specific study
 location: 0°19 N, 34°52 E. The study groups were part of a long-term
 project that began in 1979. During the 2006-2020 period, each group was
 monitored on a near daily basis, and the appearance of newborn infants was
 noted on each observation day. Further details about the data collection
 are available in the associated publication.
description: The dataset (Cords_Gometz_2021_Dataset) represents 484 births,
 one per row. For each birth, the data set includes information on the
 following variables, listed from left to right. 
 <strong>kidDOB</strong>: the date of the birth
 (YYYY-MM-DD); <strong>momID</strong>: a
 unique identity code for each mother (note that some mothers have multiple
 births in this data set) 
 <strong>group</strong>: the identity (name) of the group in
 which the birth occurred. A particular mother could give birth in more
 than one group because some groups fissioned during the study period, and
 daughter groups received new names; 
 <strong>daytimebirth</strong>: expresses whether the birth
 occurred during the daytime (daylight hours), coded 0/1
 (no/yes) <strong>dies365</strong>:
 expresses whether the infant died within 365 days of its birth, coded 0/1
 (no/yes) <strong>kidsex</strong>: F for
 female, M for male. Blanks represent missing data (infant not
 sexed). <strong>kidbirthmonth</strong>:
 the month of the birth (1-12 representing January-December)
 <strong>devpeak</strong>: binary variable
 expressing the degree to which the birth month deviated from the
 population peak of births in January-February; coded 0 if birth month was
 0-4 months away from January-December peak (i.e. birth in September
 through June), or 1 if birth month was 5 months away from peak (births in
 July-August). 
 <strong>Nfems_in_hier</strong>: count of the number of adult
 females in the group, and in the group’s dominance hierarchy, during the
 year of the birth 
 <strong>st_Nfemsinhier</strong>: Z-score of previous
 variable <strong>momrank</strong>:
 mother’s dominance rank, expressed on a scale from 0 (lowest) to 1
 (highest). Ranks were assigned for each group and year based on the
 outcome of decided dyadic agonistic encounters among the group’s large
 juvenile and adult females. These are females that turned 5 years old in
 the year of the birth, or who had turned 5 years old previously. Ranks
 were computed via the I&SI method, implemented in Domicalc (Schmid
 and deVries 2013, <em>Animal Behaviour </em>86: 1097-1105).
 Publication provides further details. 
 <strong>st_momrank</strong>: Z-score of the previous
 variable <strong>momageatbirth</strong>:
 mother’s age at the time of the birth (in years) 
 <strong>st_momageatbirth</strong>: Z-score of the previous
 variable Cells that are blank represent
 missing values.