2.2. Data collection

From 2013 to 2016, we captured adult female deer in late February or early March via a net gun fired from a helicopter (Krausman, Hervert, & Ordway, 1985). Captured deer were flown to a central processing station established for each study area where they were fitted with GPS (Global Positioning System) collars (Advanced Telemetry Systems, G2110D, Isanti, MN USA) and uniquely marked with ear tags. Collars were equipped with a mortality sensor and a Very High Frequency (VHF) transmitter. Additionally, collars were programmed to collect one GPS location every 90 min and to drop off approximately 1 year following deployment (McKee et al., 2015). We determined nutritional condition of adult females using standard protocols developed and validated for mule deer (Monteith et al., 2013). Those methods used measurement of subcutaneous fat on the rump using ultrasonography, as well as palpation at rump, ribs, and withers to determine a body condition score (Cook, Stephenson, Myers, Cook, & Shipley, 2007; Monteith et al., 2013; Stephenson, Bleich, Pierce, & Mulcahy, 2002). Pregnancy status also was determined using ultrasonography (Stephenson et al., 1995). Pregnant individuals were then fitted with a vaginal implant transmitter (VIT) that was equipped with both a temperature and a photo sensor (Advanced Telemetry Systems, M3930L; Bishop et al., 2007). Individuals captured nearby were then released from the central processing station or flown back to the original capture location if they were captured over 8 km from the processing station.

Vaginal implant transmitters used during this study were similar to those described by (Bishop et al., 2011). In addition to the temperature sensor traditionally equipped in VITs used in previous studies (Bishop et al., 2007; Carstensen, DelGiudice, & Sampson, 2003; Johnstone‐Yellin, Shipley, & Myers, 2006), VITs in this study also had a programmed photo sensor. This design allowed for VIT expulsion to be detected at night or during the day despite high ambient temperatures in our study site. When a VIT was expelled, a preprogrammed Precise Event Timing (PET) coding was emitted once per minute within the VHF pulses to aid in the identification of expulsion time. The PET coding indicated the time since expulsion in 30‐min increments up to 5 days (Advanced Telemetry Systems, 2017; Bush, 2015), thereby allowing age of the neonate to be calculated precisely.

For clarification, we use the term neonate to describe an offspring in the first week of life and the term young or juvenile for all ages thereafter. Ground crews monitored females outfitted with VITs from 1 May until parturition. Monitoring occasions were <3 days apart for each female (usually every day) to capture neonates as close to parturition as possible or to prevent neonate mortality occurring prior to capture. If PET coding (i.e., the neonate's age) was less than 3 hr, technicians would allow time for critical bonding, and colostrum transfers between neonate and mother before approaching (White, Knowlton, & Glazener, 1972). Technicians would systematically search the area using the location of the VIT or the female's location at initial sighting as the beginning of their search radius (Quintana et al., 2016). Search times were restricted to 30 min to reduce the chance of abandonment of the neonate or stress to the female (Livezey, 1990). When neonates were not located during an initial search, ground crews returned the next day to search for the neonate using the same method (Bush, 2015).

In 2013, two of our collared adult females were pregnant but did not receive a VIT because the birth canal was too narrow to successfully insert a VIT. Additionally, we had one adult each year thereafter that exhibited similar morphology. Females that did not receive a VIT were located and checked for parturition by systematically searching for a neonate every 1–3 days (Bush, 2015). In 2013, we monitored 13 adults that had been active collars from 2012 but did not receive a VIT in 2013, using the same method. Throughout the study we also captured neonates from un‐collared individuals displaying signs of having a neonate nearby or opportunistically finding neonates while tracking or monitoring collared adults (Carstensen et al., 2003).

When a neonate was captured, it was immediately blindfolded, placed in a clean cloth bag and weighed to the nearest 0.1 kg using a spring scale (Pesola Scales, Baar, Switzerland). We measured new hoof growth to the nearest 0.1 mm with a digital caliper and measured chest girth and metatarsus to the nearest 0.1 cm. Sex, state of umbilicus, prominent vegetation type at the birth site, handling time, and a GPS location also were recorded. Finally, each neonate was fitted with an expandable VHF radio‐collar (Advanced Telemetry Systems) with the mortality switch set to 6 hr of no movement, and released.

We used several different methods to reduce abandonment caused by handling. All technicians wore nitrile gloves during handling to reduce scent transfer, and all blindfolds and weigh bags were washed in scent‐free detergent after each use and stored in scent‐free bags during transport. Additionally, technicians were required to wash all clothes in scent‐free detergent and to change clothes between capturing neonates from different mothers. We also stored the expandable collars in scent‐free bags containing native vegetation to reduce the amount of non‐native odors being transferred to the neonate (Livezey, 1990).

Age at capture for each neonate was determined using the PET coding recorded from the VIT. Nevertheless, age at capture had to be estimated for individuals caught from unmarked females or in instances where the VIT or PET coding malfunctioned. When monitoring collared females that did not receive a VIT or had a malfunctioning VIT, time and date were recorded on each occasion we encountered those females. We then used behavior of the neonate, condition of umbilicus, hoof appearance, and body size to estimate maximum possible age of those neonates (Haskell et al., 2007; Haugen & Speake, 1958; Monteith et al., 2014).

Survival of each neonate was monitored daily for the first week of life. Following the first week, each young was checked every 1–3 days until the month of August and weekly thereafter until they reached 120 days of age (4 months). We used 120 days as our measure of survival of young, because at 120 days young were completely weaned from mother and fully dependent on water sources and forage (Heffelfinger, 2006; Sadleir, 1980).

All animal capture and handling procedures were approved by the Institutional Animal Care and Use Committee at the University of Nevada, Reno Protocol # 00058 and were within guidelines established by the American Society of Mammalogists for research on wild mammals (Sikes, 2016). We also complied with capture and handling procedures developed by California Department of Fish and Wildlife.