Heat stress reduces growth rate of red deer calf: Climate warming implications

hottest, driest and highest solar radiation days year round (mean temperature = 24.5˚C in July; maximum temperature = 41.0˚C in August; air humidity = 46.2% in July; solar radiation = 28.1 MJ�m-2 in July, Fig 1). This period comprised average annual wind speed values (2.35 m�s-1) and also the lowest wind speed records year round (minimum = 1.92 m�s-1, Fig 1). The highest records in thermal stress took place between June and September, as indicated by THI index (maximum = 123.3 in July), and through June and August as indicated by THIWS index (max- imum = 70.6 in July) (Fig 1). Heat stress on calf growth Our final model clearly indicates that THI index had a negative effect on the rate of calf growth (estimate = -0.009, se = 0.001, p < 0.001, Table 2, Fig 2) and affected males and females in the same fashion (lrc x sex [male] estimate = -0.002, se = 0.001, p = 0.173, Table 2). For females of average body weight (99 kg) and age (6 yr) the model predicted birth weights of 8.3 kg and 9.0 Fig 1. From left to right top to bottom: Monthly mean and standard errors of mean and maximum daily air temperature, relative air humidity, accumulated daily solar radiation, mean wind speed and two indices of heat stress (THI, THIWS) in the study area (period 1999–2018). https://doi.org/10.1371/journal.pone.0233809.g001 PLOS ONE Heat stress and calf growth in red deer PLOS ONE | https://doi.org/10.1371/journal.pone.0233809 June 1, 2020 6 / 26