Density and reproductive characteristics of female brown bears in the Cantabrian Mountains, NW Spain

Abstract

Here we present annual nearest-neighbour distances (as a proxy of density) between females with cubs-of-the-year (hereafter FCOY) and reproductive characteristics of brown bears Ursus arctos in the Cantabrian Mountains (NW Spain), from 1989 to 2017. FCOY nearest-neighbour distances and reproduction parameters of 19 focal females followed over several consecutive years (from 2004 to 2017) were obtained from bears inhabiting the western sector of the Cantabrian Mountains, where most of the bear population resides. In contrast, general reproductive characteristics were studied in the whole Cantabrian Mountains (western and eastern sectors together) on a sample of 362 litter sizes and 695 cubs. Mean nearest-neighbour distance between FCOY was 2559 ± 1222 m (range = 1305-4757 m). Mean litter size was significantly larger in the west (1.8 ± 0.2 cubs) than in the east (1.3 ± 0.6 cubs). Mean litter size for the whole of the Cantabrian Mountains was 1.6 ± 0.3 cubs. Litter sizes of one, two and three cubs represented 33.4, 56.1 and 10.5% of observed family groups, respectively. Interannual variations in litter size were not significant for both the western and the eastern areas. Mean cub mortality was 0.2 ± 0.5 cubs and did not vary among years. Cub mortality per litter size was 3.9% for one cub, 69.2% for two cubs and 26.9% for three cubs. Mean reproductive rate of the 19 focal females was 1.5 ± 0.6 cubs (n = 58 litters). Litter size of focal FCOY did not differ from the litter size obtained from systematic observations in the whole Cantabrian Mountains. During this period, cub mortality occurred in 24.1% of the 58 litters. Females usually bred every second year (average litter interval = 2.2 years). The estimated reproductive rate for the bear population was 0.7 young born/year/reproductive adult female.

Not exodus, but population increase and gene flow restoration in Cantabrian brown bear (Ursus arctos) subpopulations. Comment on Gregório et al. 2020

“…Considering that the average litter interval for female brown bears in the Cantabrian Mountains is 2.2 years [ 50 ], the latest available figures of FCOY (6 in 2017 and 7 in 2018, Fig 1 ) indicate that there are at least 14 reproductive females in the eastern subpopulation, a much higher figure than the ~4 reproductive females that Gregório et al [ 4 ] (p. 15) claim for this subpopulation. The number of ~4 reproductive females is also inconsistent with the 25 unique genotypes of males captured by Gregório et al [ 4 ] in the eastern population, even accepting that this number must not be considered as a census.…”

Can landscape characteristics help explain the different trends of Cantabrian brown bear subpopulations?

“…If the habitat use displayed by the two brown bear subpopulations of the Cantabrian Mountains only offers limited help in explaining the differences in number and fecundity exhibited by the evolution of the two subpopulations, other factors might be acting on them. Given that (a) previous population models have partially failed in forecasting the dynamics and trends of brown bears in the Cantabrian Mountains and (b) patterns of increase and fecundity continue to be different between the west and the east (Gonzalez et al 2016;Penteriani et al 2018), we suggest that future analyses should be focused more on how the human environment can achieve coexistence with bears than on the natural landscape (Zarzo-Arias et al 2018). If habitat alone cannot help explain the different properties of the two Cantabrian bear subpopulations, then suspicions may arise around direct human influences on the different trends exhibited by the two sectors of this endangered bear population.…”

“…The number of females with cubs-of-the-year (FCOY), a proxy of the population trend, has also shown a more rapid increase in the western subpopulation than in the eastern one (6 vs. 34 FCOY in 2016 and an average of 4.3 vs. 25 FCOY during the ten year period 2007-2016; unpublished data from Gobierno del Principado de Asturias, Junta de Castilla y León, Gobierno de Cantabria and Xunta de Galicia; Palomero et al 2007). Mean litter size is 1.8 ± 0.2 cubs (n = 596 cubs) in the west and 1.3 ± 0.6 cubs (n = 99 cubs) in the east, with the former being significantly larger than the latter (Mann-Whitney test Z = -4.66, P = 0.0001, n = 29, 27) (Penteriani et al 2018). Thus, despite the consistent positive trend in population size of the western subpopulation of Cantabrian brown bears, the eastern subpopulation has had a substantially smaller population increase (Martínez Cano et al 2016).…”

Seasonality, local resources and environmental factors influence patterns of brown bear damages: implications for management

“…In order to test the potential influence of the size of each bear population on the amount of damage, we also took into consideration an annual estimation of the number of bears for each nucleus. For the Cantabrian population, we used the yearly number of females with cubs of the year for each Cantabrian subpopulation as a proxy of population size, since they are easier to locate and distinguish right after they exit the den after hibernation, as they stay in the same area for several weeks (Ordiz et al ., 2007; Penteriani et al ., 2018). For the Pyrenean population, the total number of bears was available, because it is estimated by the different administrations based on direct observations, camera traps and genetic analyses of bear hair and scats.…”