We are pleased to share these recent Ursus articles with you. Thanks to the support of subscribing institutions and the global library community, the BioOne Subscribe to Open (S2O) threshold has been reached, making all Ursus articles open access for 2026. This milestone represents a significant step forward in making research accessible to everyone. Read the announcement from BioOne.
Rescued Bornean sun bear cub mass increases during rehabilitative hand-rearing
Ellen Susan Wieczorek, Siew Te Wong, Boon Nie Yeoh
Ursus 2026 (37e9), 1-14, (6 July 2026). https://doi.org/10.2192/URSUS-D-24-00020
KEYWORDS: cub, growth, hand-raised, Helarctos malayanus euryspilus, mass, milk, sun bear, weight
The amount and composition of milk used in hand-raising ursids significantly influences development, growth rates, abnormalities, and survival rates of cubs. This study analyzes hand-raised cub feeding (mL/kg) and mass (kg) data for Bornean sun bear (Helarctos malayanus euryspilus) cubs collected at the Bornean Sun Bear Conservation Centre in Sabah, Malaysia, since 2013 to provide comparisons for practical application. Using a linear model to assess growth rates through mass and using a generalized linear mixed model with random effects (GLMMer) to model the mass increases of 10 hand-reared cubs from daily or semiweekly measurements, we determined whether differences between males and females were due to sexual dimorphism. We found that average male mass (ȳ2= 16.1 kg) was 26.7% more than average female mass (ȳ3 = 11.8 kg) with similar results for each quantiled age group. Significant response variables identified were sex, age, milk volume fed, individual bear health status, and the Random Milk Variable, although other masking variables may exist. The milk formula amounts (g/mL) fed to each bear varied by mass (kg) as well as individual, random bear health status, and milk variation due to clinical judgement captured through the Random Milk Variable. This model allowed us to support the hypothesis of sexual dimorphism in sun bears at an early age. Additional research should assess sun bear milk composition to more closely simulate natural milk for cubs in rehabilitation.
Detecting occurrence and timing of grizzly bear parturition based on anomalies in accelerometer data
Lori L. Roberts, Cecily M. Costello, Milan A. Vinks, Daniel D. Bjornlie, Matthew D. Cameron, Justin G. Clapp, Mark A. Haroldson, Grant V. Hilderbrand, Kyle Joly, Wayne F. Kasworm, Jeremy M. Nicholson, Thomas G. Radandt, Mathew S. Sorum, Justin E. Teisberg, Frank T. van Manen
Ursus 2026 (37e10), 1-12, (17 July 2026). https://doi.org/10.2192/URSUS-D-25-00008
KEYWORDS: activity sensor data, anomaly detection, birth timing, denning, grizzly bear, parturition, reproduction, Ursus arctos
Documenting natality of brown (grizzly) bears (Ursus arctos) is an important component of many population monitoring and research programs. Brown bears give birth during hibernation, so observation of litters is generally not feasible until females exit dens, and detection of litters can be compromised by poor observability. Using triaxial accelerometer activity data stored on radiocollars, we developed a technique that predicts births by the presence of brief upsurges in activity likely associated with postnatal maternal behaviors. We developed presence criteria with a training sample of known parturient females (n = 22) to detect anomalies within time-series of daily motion-counts (i.e., activity readings >0 measured at 10-min intervals) during 25 December–7 March. To test performance, we applied criteria to a blinded sample of activity data obtained from female grizzly bears (captured and collared during 2012–2022) in 4 populations in interior North America (n = 295). We assigned predicted status and compared assignments to reproductive status at first visual observation. The true positive rate was 91% (n = 47 females observed with cubs of the year) and the false-positive rate was 17% (n = 65 females observed with older offspring). Births were predicted for 50% of females with unknown reproductive status (n = 48), 21% of females observed without offspring (n = 114), and 10% of subadult females considered too young to reproduce (n = 21). Dates of predicted births varied from 27 December to 28 February. Our anomaly detection technique was successful at estimating parturition events, and despite some error, indicated that a number of litters were born but not observed, presumably due to mortality in or shortly after den emergence. This technique provides an additional tool for supplementing visual observations for natality estimation and population modeling, provided that potential biases stemming from increased detection rates are considered.