Abstract 280 – Wild sun bears (Helarctos malayanus) exhibit aseasonality in parturition

Zachary David, Brian Crudge, Matt Hunt, Kirsty Officer, Vuthy Choun, Barbara
Durrant, Megan Owen, Morokot Long, John Whiteman

Seasonal reproduction can provide species with fitness advantages by allowing the birth of
young to coincide with favorable environmental conditions, particularly in regions with highly
seasonal temperature, precipitation, or other conditions. The family Ursidae is a useful system
to study reproductive timing, as there are only eight extant species which are widely
distributed, and which experience a large range of variation in environmental conditions. Seven
of the bear species reproduce seasonally in both managed care and the wild; however, data for
the eighth species, the sun bear (Helarctos malayanus), are unclear. Sun bears have reproduced
throughout the year in managed care, yet currently there are no clear data of birth timing for
wild sun bears. Here we investigate the seasonality of parturition of wild sun bears by utilizing
body mass measurements from bears placed in the care of the wildlife conservation
organization Free the Bears in Cambodia after interception by authorities for illegal removal
from the wild. We selected body mass records for all rescued bears ≤ 5kg, and modeled growth
rates with linear regressions for cubs with > 3 measurements. Assuming a mass of 300g at birth,
these growth rates were used to estimate the birth date for each cub. Our results suggest that
wild sun bears reproduce aseasonally in Cambodia, with estimated birth dates occurring in all
12 months of the year and all 4 of Cambodia’s distinct seasons.