Reproductive success, calf survival, and spatial relationships of elk in Pennsylvania
Restricted (Penn State Only)
- Author:
- Corondi, Avery
- Graduate Program:
- Wildlife and Fisheries Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- May 24, 2023
- Committee Members:
- Bradley Cardinale, Program Head/Chair
W. David Walter, Thesis Advisor/Co-Advisor
Justin D Brown, Committee Member
Duane R Diefenbach, Committee Member
Jeremiah E Banfield, Special Signatory - Keywords:
- Cervus canadensis
elk
free-ranging
survival
immobilization
maternal attentiveness - Abstract:
- Effective species management of a population requires timely assessment and quantification of recruitment, a basic demographic parameter which includes female reproductive success, neonate survival, and cause-specific mortality. This is especially true in small, hunted populations, like the re-introduced population of elk (Cervus canadensis) in northcentral Pennsylvania. While knowledge of a single parameter provides insight, a combined understanding of these parameters would facilitate a more comprehensive approach to management. Pregnancy rates are not only indicative of female health but are also indicators of external factors that result in population changes. However, pregnancy rates do not necessarily equate to the number of calves that enter the population. Assessment of intrauterine mortality provides necessary information for a process that starts at conception and ends at calf recruitment. Intrauterine mortality is difficult to assess, especially in free-ranging populations, and is often not considered in species management. Additionally, birthing complications can lead to neonatal death immediately before, during, or shortly after birth. These cases are often overlooked unless birth sites can be located. Viable neonates that enter the population are vulnerable to many sources of mortality prior to recruitment age, especially in predator-rich environments. Neonates are cited as the most variable life stage and the most influential in population trajectories. As such, accurate estimates of neonate survival, how they may change over time, and cause-specific mortality are of particular importance. From 2013 to 2017, blood samples were collected from harvested elk in Pennsylvania, which occurs approximately 1 month after the presumed end of their mating season. Pregnancy was determined using a serum-based pregnancy specific protein B (PSPB) assay. A five-year mean of pregnancy rates for females revealed a 52% pregnancy rate. This low proportion prompted live-capture of elk in winter to assess pregnancy rates at later dates, potentially allowing females more time to conceive. A two-year mean of live-capture blood collections resulted in an 87% pregnancy rate, suggesting that females may be conceiving asynchronously and later than other elk populations in North America. Later-bred females give birth to calves later in the summer, potentially influencing calf survival. To further assess pregnancy rates, document dates of parturition, and investigate calf survival, a study using vaginal implant transmitters (VITs) was initiated in winter 2020. Vaginal implant transmitters are deployed in pregnant females paired with a GPS collar, which monitors the VIT’s status. The VIT is expelled with the calf at parturition and a notification is sent to researchers, allowing for rapid location and collaring of the calf. To deploy VITs, 208 females were chemically immobilized. There are several drug combinations suitable for immobilizing elk, however, data is lacking for comparison between drug combinations in free-ranging elk. Two drug combinations, butorphanol-azaperone-medetomidine (BAM) and nalbuphine-medetomidine-azaperone (NalMed-A) are frequently used. We compared BAM and NalMed-A based on vital rates during sedation, time for induction and reversal, sedation quality, and the need for supplemental drug doses to reach adequate sedation. Elk in the study were administered drugs through CO2-powered remote-delivery systems using either a rifle (hereafter termed free-darting) or with a pistol after the elk was physically captured in a modified Clover trap. We found no effect of drug on vital rates and induction and reversal durations. There were higher frequencies of poor sedation quality and supplemental drug doses when using NalMed-A. We assessed pregnancy of chemically immobilized elk using transrectal ultrasound, which was later confirmed by PSPB. Vaginal implant transmitters were only deployed when pregnancy could be confirmed by ultrasound. From 2020 to 2022, 150 VITs were deployed. Females that were yearlings or determined to likely be senescent based on dentition were removed from pregnancy rate assessment, which was 79% over the three-year study. When yearlings and senescent females (8 out of 208 elk immobilized) were included in pregnancy rate determination, the proportion decreased to 75%. Seven females retained their VITs through calving season and one expelled a dead fetus pre-term. We found evidence of intrauterine mortality by re-examining the females and found new pregnancies even with a VIT present, indicating abortion likely occurred at some point after VIT insertion, the fetus was resorbed, and the female was re-bred the following mating season. Based on this evidence, approximately 5% of females that received VITs experienced intrauterine mortality. Out of 150 VITs, 127 resulted in a viable calf. Five calves were found dead at the birth site and 44 calves died before reaching one year of age. Predation was our leading cause of mortality. Other causes of mortality included peristillbirth, trauma, starvation, malnutrition/tick infestation, harvest, disease, and unknown cause. We built known-fate models using date of birth, sex, and birth mass. Our top model indicated that date of birth best described calf survival. Based on that model, a calf born on the mean birth date of 17 June had an annual survival rate of 0.590 (95% CI = 0.486 – 0.686), with survival decreasing with later birth date. The overall probability a calf survived to 1 year of age was 0.634 (95% CI = 0.535 – 0.723). We fit both the mother and calf with GPS collars, allowing us to investigate their spatial relationship and document novel data as GPS collars have rarely been used on elk calves. The collars recorded locations every hour at the same time for the first 6 weeks after parturition. We measured the distance between the synchronous points and classified distances in defined categories (≤25 m, >25 – 200 m, and ≥200 m). We found that mother-calf pairs spent most of their time 25 – 200 m apart and increased the proportion of time spent <25 m apart as calves aged, regardless of calf fate. Calf recruitment is the product of fecundity, pregnancy success, and survival of calves both pre- and post-weaning. Adequately assessing recruitment requires reliable data for each component, which is often challenging and costly in free-ranging populations. We assessed fecundity via transrectal ultrasound on immobilized elk, where we found BAM produced a more stable sedation than NalMed-A, though both performed effectively respective of the procedures performed. We used VITs to determine dates of parturition, approximate the proportion of females that successfully produced a viable calf, and to determine cause-specific mortality of calves to 1 year of age. Lastly, we used novel GPS collars to investigate maternal attentiveness during the most vulnerable period in calf development. Advances in technology have allowed us to assess the components of recruitment more accurately than previous research to better inform management decisions. Our study lends evidence to the importance of evaluating these components collectively to gain a broader understanding of recruitment. Also, it highlights the need to conduct investigations of basic population parameters regularly to detect potential temporal changes that would otherwise go unnoticed.