Influence of intrinsic and extrinsic attributes on neonate survival in an invasive large mammal

Abstract

Understanding factors influencing survival of neonates for wild species is important for successful management, particularly for determining drivers of population dynamics. Wild pigs (Sus scrofa) are invasive and populations are rapidly increasing in part due to high reproductive capacity. Survival of adults is generally high, however, survival of piglets, and particularly neonates, is largely unknown. We located neonates at the natal nest and quantified survival in relation to individual and maternal biological attributes, and environmental variables. During 2017–2020, we captured 50 neonates from 13 litters and documented 28 mortalities (56%) over six weeks. Survival was positively influenced by pelage coloration, likely as a form of camouflage from predators. Male neonates had higher survival. They were born larger than females, which could be beneficial for thermoregulation and competition for milk. Neonates born to larger sows had lower survival. Sow size was positively correlated with litter size, and this finding may reflect the increased nutritional demands of sustaining large litters, or difficulties in defending more neonates against predators. Neonates born in warmer months had higher survival than those born in cooler months. Neonates are inefficient thermoregulators, thus being born in warmer months could be beneficial for maintaining homeostasis as well as access to more food resources. These are the largest and most complete data for neonate wild pig survival and will inform population models for the development of management strategies to reduce negative impacts of this destructive invasive species on native ecosystems.

Factors influencing pregnancy, litter size, and reproductive parameters of invasive wild pigs

“…Farrowing may require the female to stay close to the nest to care for the neonates and will likely decrease time spent foraging (Chinn et al 2021), which may be limited by nutritional condition during pregnancy.…”

“…Despite annual reproduction, our data revealed females were less likely to be pregnant during July and August, possibly because food availability may be declining and conditions may be less favorable for pregnancy by the end of summer. In addition, with a 4‐month gestation period, farrowing in the winter could be less optimal for neonate survival (Chinn et al 2021).…”

“…We collected tissue (ear biopsy) from all sampled pigs for genetic analysis and whole blood from a subset of pigs for use in hormonal assays. We collected whole blood from euthanized wild pigs via cardiocentesis or from the jugular vein for live-captured pigs (from other research studies; Chinn et al 2021). We centrifuged blood for 10-15 minutes at 2,500 revolutions per minute (rpm) and stored serum at −80°C until analysis.…”

“…Specifically, within hours of ovulation, a CL develops and there is a noticeable distended region where the ovum erupted. For live-captured females, we determined pregnancy by ultrasound and tracked females via transmitters until farrowing and neonate sampling (Chinn et al 2021). We included data from live-captured individuals in reproductive hormone, phenology, age class, and litter size analyses.…”

Model selection isn't causal inference

“…Morton et al 2021 What is the impact of wildlife trade on terrestrial biodiversity? Chinn et al 2021 What is the influence of intrinsic and extrinsic attributes on neonate survival in wild pigs? Montano-Centellas et al 2021 What are the ecological drivers of avian community assembly along a tropical elevation gr Rode et al 2021 What are the combined effects of sea ice, seal body condition and atmospheric circulation Sinnott-Armstrong et al 2021.…”