DOI: 10.5061/dryad.7sqv9s52b
title: Thermal conditions alter the mating behavior of males in a polygynous system

description: Males in polygynous systems may be facing a tradeoff between the traits
 that enhance reproductive success and the need to cope with environmental
 change. To secure mates, males invest into large bodies, lavish ornaments,
 and costly activities, but these investments may be incompatible with
 future environments. As climatic change intensifies, thermal stressors
 could be disrupting the energy-intensive pathways that historically have
 yielded mating opportunity. We evaluated how traits associated with social
 dominance interacted with environmental conditions to shape mating
 behavior and opportunity in moose (Alces alces), a heat-sensitive species
 in which southern populations live at the edge of their thermal tolerance.
 We anticipated that males with favorable characteristics (e.g., age,
 weaponry) would allocate more to reproduction, resulting in increased
 mating opportunity. We expected that warm temperatures would limit
 reproductive effort, especially as age and weapon size increased. We
 quantified mating tactics, effort, and opportunity for male moose ranging
 in age from 1.5 to 11.5 years. We used hidden Markov models to detect
 mating tactics, accelerometer data to quantify movement effort, and
 proximity to females as a proxy for mating opportunity. We modeled these
 mating dynamics as a function of age, weapon size, and ambient
 temperature. Warm temperatures exaggerated age-related differences in time
 and effort allocated to reproductive movement. Heat disproportionately
 limited reproductive effort in old males, the ages that also had the
 greatest mating opportunity. Even though warm temperatures altered mating
 behavior, they did not reduce mating opportunity. Across temperatures,
 mating opportunity was highest in prime-age and old males, yet time and
 effort devoted to reproductive movement decreased with age. Climate
 change, which is increasing autumn temperatures, may increase variation in
 reproductive effort across ages and depress the movement of old males, who
 are typically the primary breeders. The discrepancy between behavior and
 opportunity suggests that movement is not a reliable pathway to
 reproduction and emphasizes the advantages of energy-saving strategies,
 especially as environments become more taxing for heat-sensitive species.
 We reveal the limitations of movement effort in polygynous mating
 strategies and the susceptibility of this critical life history stage to
 environmental change.
description: <strong>Animal Capture and
 Handling</strong> We chemically immobilized male
 and female adult moose (≥1 year) via helicopter (Levine et al. 2022). For
 the duration of the study, we sought to maintain 15 collared animals of
 each sex (approximately 30% of the population). We determined age via
 cementum annuli (Matson’s Laboratory, Milltown, MT) using the right,
 incisiform canine (Swift et al., 2002). We fitted all moose with GPS
 collars (VERTEX PLUS; Vectronic Aerospace GmBH). All GPS collars had
 hourly fix rates and three orthogonal accelerometers collecting 5-min
 averaged activity data. In autumns of 2020 to 2022, we classified antler
 size of GPS-collared male moose through field observation and
 photography. <strong>Movement
 Metrics</strong> To quantify mating tactics
 (mate-searching and female-defense), we identified likely behaviors with a
 three-state hidden Markov model (momentuHMM package) parameterized with
 the step length and turn angle of movement. Our model classified hourly
 GPS locations as either encamped, tortuous, or exploratory states. To
 further specify and validate mating behaviors, we visually inspected which
 of the three states aligned with known interactions between GPS-collared
 male and female moose (i.e., female-defense). The encamped and tortuous
 states were both associated with bouts of female interaction. We therefore
 manually validated a bedded state (&lt;20m step length; Verzuh et al.,
 2021) as the distance of typical GPS error for a stationary collar,
 grouped the encamped and tortuous states into a single female-defense
 state, and designated the remaining exploratory movement as mate-searching
 behavior. To quantify mating opportunity (proximity to females), we summed
 the number of hourly fixes in which a male was ≤50 meters from a collared
 female each day of the focal period (wildlifeDI package).
 <strong>Antler Classification</strong>
 Scoring systems for moose are different than other cervids
 because the palmate structure creates more diverse antler morphologies
 than the tine-based scoring of cervine antlers (Wright & Nesbitt,
 2003). We used existing methods of classification derived for larger
 subspecies, Boone and Crockett standards, and harvest records for Shiras
 moose to inform our scoring system. The scoring system (1–5) was based on
 antler form, palm structure, standard size approximations (spread, height,
 and width), and qualitative estimates of size relative to the head and
 ears. We estimated measurements when possible, using the length of the ear
 (20cm) and distance between the pedicles (17.5cm).
 <strong>Environmental Data</strong>
 We used ambient temperatures from the center of the study area
 (43°52'N, 109°19'W; Kirwin Snotel 560) to calculate daily
 maximum temperature.
description: # Thermal conditions alter the mating behavior of males in a polygynous
 system
 [https://doi.org/10.5061/dryad.7sqv9s52b](https://doi.org/10.5061/dryad.7sqv9s52b) ## Description of the data and file structure Movement metrics and individual data for moose in northwestern Wyoming during the mating season (2020-2022). ### Files and variables #### File: FE-2024-00544\_Ages.txt **Description:** Animal ages in years. ##### Variables * AID: Unique ID for each animal. * "CaptYr: Year of tooth extraction. * Age: Age in years of tooth when extracted. #### File: FE-2024-00544\_AntlerScore.txt **Description:** Animal antler scores. ##### Variables * AID: Unique ID for each animal. * FallYear: Year of antler growth. * Score: Score of antler (1-5). #### File: FE-2024-00544\_Activity.txt **Description:** Activity data. ##### Variables * AID: Unique ID for each animal. * DateMST: Date and time of collection. * axD: Accelerometer value, X-axis. * ayD: Accelerometer value, Y-axis. * azD: Accelerometer value, Z-axis. #### File: FE-2024-00544\_Proximity.txt **Description:** Proximity to females. ##### Variables * AID: Unique ID for each animal. * Year: Year. * DayNum: Day number of year. * Count: Hours of day in contact with tagged female. #### File: FE-2024-00544\_BehStates.txt **Description:** Hourly behavioral states. ##### Variables * AID: Unique ID for each animal. * DateMST: Date and time of collection. * states: Behavioral state. #### File: FE-2024-00544\_HourlyAirTemp.txt **Description:** Temperature at KirwinSNOTEL. ##### Variables * Date: Date and time of collection. * Air Temperature Observed (degF): Ambient temperature. **Please contact Rebecca Levine ([rlevine1@uwyo.edu](mailto:rlevine1@uwyo.edu)) for questions related to the data.**