Activity patterns of black bears in relation to sex, season, and daily movement rates

—Activity patterns of animals can vary depending on both endogenous and environmental factors. Although black bears exhibit substantial variation in activity across the year, relatively little is known about how daily activity patterns and associated movement rates differ among sex and age classes across seasons. We used fine-scale movement data from black bears fitted with GPS collars to evaluate movement and activity patterns across sex and age classes for daily and seasonal time periods in relation to mating and foraging behavior. Black bears were most active during crepuscular time periods, moderately active during the day, and least active at night, which is consistent with previous research on black bear activity patterns in areas where bears were not greatly influenced by human activities. However, during spring and early summer, adult males moved significantly more during the crepuscular time period than they did during late summer and fall. Female and subadult males exhibited very similar activity patterns between seasons; and during late summer and fall, all bear classes exhibited similar activity patterns across daily time periods. Differences in activity patterns of males between seasons were potentially related to extensive movements undertaken during the mating season. Although adult males exhibited lower movement rates in late summer and fall compared to spring and early summer, females and subadult males did not appear to reduce movement rates during the late-summer berry season. Our research reveals that, although bear classes exhibit similar temporal patterns of daily activity and inactivity, the magnitude of movement rates revealed differences in activity patterns among bear classes, which allowed us to better understand factors influencing activity in animal populations. RESUMEN.—Los patrones de actividad de los animales pueden variar dependiendo, tanto los factores endógenos, como los ambientales. A pesar de que los osos negros exhiben gran variación en su actividad durante el año, se sabe relativamente poco acerca de cómo los patrones de actividad cotidiana y las tasas de movimientos asociados difieren entre los sexos y clases de edad a lo largo de las estaciones. Usamos datos de escala fina del movimiento de los osos negros, a través de collares con sistema de posicionamiento global (SPG), para evaluar los patrones de movimiento y actividad por sexo y por clases de edad, durante periodos de tiempo diarios y estacionales con relación al comportamiento de apareamiento y de forrajeo. Los osos negros fueron más activos durante los periodos de tiempo crepuscular; moderadamente activos durante el día y menos activos durante la noche, lo cual es consistente con las investigaciones previas en las que se evaluaban los patrones de actividad del oso negro en lugares donde no eran fuertemente influenciados por las actividades humanas. Sin embargo, durante la primavera y el comienzo del verano, los machos adultos se movieron significantemente más durante los periodos crepusculares, comparado con el final del verano y el otoño. Las hembras y los machos subadultos mostraron patrones de actividad muy similares entre las estaciones; y para finales del verano y el otoño, todas las clases de osos exhibieron patrones de actividad similares durante los periodos de tiempo diarios. Las diferencias en los patrones de actividad de los machos entre estaciones se relacionaron potencialmente a los extensos movimientos emprendidos durante la época de apareamiento. A pesar de que los machos adultos exhibieron tasas bajas de movimiento a finales del verano y en el otoño, en comparación con la primavera y principios del verano, las hembras y los machos subadultos no aparentaron disminuir las tasas de movimiento durante la época de bayas al final del verano. Nuestra investigación muestra que, a pesar de que las clases de osos exhiben patrones temporales similares de actividad e inactividad diaria, la magnitud de las tasas de movimiento reveló diferencias en los patrones de actividad entre las clases de osos, lo cual nos permitió entender mejor los factores que influyen en la actividad de las poblaciones de animales. Movements and activity patterns of American black bears (Ursus americanus) can vary depending on season, forage availability, gender, age, social interactions, and time of day (Garshelis and Pelton 1981, Young and Ruff 1982, Ro gers 1987, Schwartz and Franzmann 1991, Po well et al. 1997, Samson and Huot 1998, Schwartz et al. 2010). In addition, human presence and behavior can strongly influence activity patterns of black bears. In areas where black bears avoid human food resources or do not experience substantial human disturbance, bears are most active during diurnal and crepuscular time periods and exhibit a bimodal pattern of activity (Amstrup and Beecham 1976, Lindzey and Meslow 1977, Ayres et al. 1986, Larivière et al. 1994, Beckman and Berger 2003). In contrast, in places where bears either exploit human food resources or are sufficiently disturbed by human activities, bears demonstrate greater activity during nocturnal time periods (Ayres et al. 1986, Beckman and Berger 2003, Matthews et al. 2006). Thus, black bears appear to demonstrate plasticity in their activity patterns and adapt their movements in response to their environment, including anthropogenic sources of disturbance. Previous studies quantifying activity of black bears interpreted signal patterns from very high frequency (VHF) collars with activity switches that emit a different signal when the collar is moving. Activity switches on GPS collars have also been used to evaluate activity of black bears in a similar fashion. These data effectively discriminate between resting and active bears (Lindzey and Meslow 1977, Garshelis and Pelton 1980, Ayres et al. 1986, Larivière et al. 1994, Matthews et al. 2006, Schwartz et al. 2010); however, the magnitude of activity or rate of movement cannot be evaluated using these methods. Therefore, although 2 indi viduals might demonstrate identical binary activity patterns (i.e., active or inactive), they could exhibit marked differences in behaviors and movements during active periods. For ex ample, an animal would be classified as active if it moved 0 m and was grooming itself or if it was traveling at a rapid pace across the landscape. Thus, our understanding of activity patterns of animals would be advanced by measuring activity on a continuous scale of movement to understand the magnitude of activity across daily and seasonal time periods. GPS collars can record locations at frequent time intervals throughout daily time periods, enabling researchers to evaluate finer-scale patterns of animal movements and the magnitude of activity. Our objective was to evaluate fine-scale movements for black bears across sex and age classes during daily and seasonal time periods to understand how humans, the bear mating season, and seasonally available food resources influence activity patterns. If bears were habitu ated to human foods, we expected animals to be most active at night; and if bears were not habituated to human foods, we predicted that animals would exhibit a bimodal daily activity pattern, with animals being most active during crepuscular time periods. We expected that the activity patterns of bears in this study would be consistent with patterns of habitat selection where bears avoided areas of human development, as demonstrated in previous studies. If activity patterns were driven by the mating season, we expected adult males to increase movement rates when they engaged in mateseeking behavior during spring and early summer, and we predicted that other age-sex classes would not demonstrate different move ment patterns between seasons. If activity patterns were driven by the presence of seasonally available berries in late summer and fall, then we expected that movement rates for all bear classes would decline during the berry season compared to the nonberry season, because bears would concentrate foraging behavior within berry patches and ex hibit more continuous activity throughout the day. If both the mating and berry seasons in fluenced bear movements, then we expected both of the patterns described above to be evident.