Hair Growth in Brown Bears and Its Application to Ecological Studies on Wild Bears

Jimbo, Mina; Matsumoto, Naoya; Sakamoto, Hideyuki; Yanagawa, Yuchio; Torii, Yoshiko; Yamanaka, Masami; Ishinazaka, Tsuyoshi; Shirane, Yuri; Sashika, Mariko; Tsubota, Toshio; Shimozuru, Michito

doi:10.3106/ms2020-0021

Cited by 10 publications

(15 citation statements)

References 28 publications

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“…We classified the growth stages of the hair based on the shapes of hair bulbs according to Jimbo et al (2020). The shape of the hair bulbs was classified into three types by gross observation: black hook (hereinafter BH type), which indicated that hairs were growing in the current year of capture; white hook (hereinafter WH type), which indicated that hairs almost stopped growing during the current year of capture; and white sphere (hereinafter WS type), which indicated that hairs had grown during the previous year of capture (Jimbo et al, 2020).…”

Section: Methodsmentioning

confidence: 99%

“…The age data that were used for our analysis were modified based on the age when the hair grew. If a hair was determined to be from the previous year based on the shape of the hair bulb (Jimbo et al, 2020), the age was determined to be the estimated age at the time of capture minus 1 year. The bears of each sex were classified into three age classes: juvenile, sexually mature adult, and physically mature adult.…”

Section: Bear Hair Collection and Data Curationmentioning

confidence: 99%

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Diet selection and asocial learning: Natal habitat influence on lifelong foraging strategies in solitary large mammals

et al. 2022

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Exploring the process of diet selection will contribute to improvement in our understanding of animal foraging strategies. The overwhelming majority of ecological research on animal learning and foraging concentrates on how social learning influences the feeding styles of animals living in groups. In solitary animals that live long after independence from their mothers, foraging experience after independence is expected to have a significant influence on diet selection, but few studies have addressed this point. We used brown bears (Ursus arctos), which spend 1–2 years with their mothers before foraging alone, as a model species and investigated how their diet changed later in life. We estimated the diets of bears at the individual level by using stable isotope analysis of guard hairs and examined the factors that drove dietary variation. We also quantified the extent to which the diets of bears shifted by comparing the diets of bears at the time of capture with the average diet in their natal habitat. Our results indicated that females retained the average diet of their natal habitat, whereas the diets of males significantly changed more than 6 years after becoming independent from their mothers, when they reached physical maturity. Males were dependent on energy‐rich marine animals at older ages regardless of their natal habitats, which we attribute to several factors, including habitat exploration, acquisition of foraging experience, and social dominance. Our results provide the first evidence, suggesting that foraging experience after independence influences diet selection later in life in solitary large mammals.

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Section: Methodsmentioning

confidence: 99%

Section: Bear Hair Collection and Data Curationmentioning

confidence: 99%

Diet selection and asocial learning: Natal habitat influence on lifelong foraging strategies in solitary large mammals

et al. 2022

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“…We included in the analysis only hairs collected in June (pre www.nature.com/scientificreports/ moult) and September (post moult), and excluded those sampled in July and August (i.e., during the moult) due to high uncertainty of their assignment. Starting from the root up to the tip of the hair, we cut guard-hairs with a surgical scalpel into 15-mm sections, which we assumed to correspond approximately to the hair growth of 1 month 40,61,62 . Specifically, for fully-grown hairs sampled in June we assigned the basal 15-mm section to the last month of growth before dormancy (November) in the previous year, the successive 15-mm section the month before (October), and so on.…”

Section: Methodsmentioning

confidence: 99%

“…Instead, the basal 15-mm section of hairs sampled in September was assigned to the last month of growth before the actual sampling date, the successive 15-mm section to the month before and so on. However, to account for the inherent uncertainty in the monthly growth rate of hair sections 40,[60][61][62] , we conducted the analysis at a seasonal resolution by pooling 15-mm hair sections across dietary seasons. These were defined based on the phenology of seasonal key foods for Apennine bears 13 : Spring, including sections whose growth was assigned to the months of March, April and May; Early summer, including sections assigned to June and July; Late Summer, including section assigned to August and September; Autumn, including hair sections assigned to October and November.…”

Section: Methodsmentioning

confidence: 99%

“…Therefore, a temporal sequence in diet composition can be retrospectively read across hair sections, progressing from the tip to the root of the hair 57 . Bears have a single annual moult, occurring in a lapse of time that spans from spring to summer 40 , 60 – 62 , and hair growth, at an approximate rate of 15 mm/month, lasts for the entire period of activity each year, from the moult until dormancy 40 , 60 – 62 . Therefore, comparing isotopic values of sequential sections of the hair provide a means to investigate variation in the diet that may take place during the hair growth period 26 , 57 , 59 , 60 , 63 .…”

Section: Introductionmentioning

confidence: 99%

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Gaining insight into the assimilated diet of small bear populations by stable isotope analysis

Careddu

Ciucci

Mondovì

et al. 2021

Sci Rep

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Apennine brown bears (Ursus arctos marsicanus) survive in an isolated and critically endangered population, and their food habits have been studied using traditional scat analysis. To complement current dietary knowledge, we applied Stable Isotope Analysis (SIA) to non-invasively collected bear hairs that had been individually recognized through multilocus genotyping. We analysed carbon (δ13C) and nitrogen (δ15N) stable isotopes of hair sections and bear key foods in a Bayesian mixing models framework to reconstruct the assimilated diet on a seasonal basis and to assess gender and management status effects. In total, we analysed 34 different seasonal bear key foods and 35 hair samples belonging to 27 different bears (16 females and 11 males) collected during a population survey in 2014. Most bears showed wide δ15N and δ13C ranges and individual differences in seasonal isotopic patterns. Vegetable matter (herbs, fleshy fruits and hard mast) represented the major component of the assimilated diet across the dietary seasons, whereas vegetable crops were rarely and C4 plants (i.e., corn) never consumed. We confirmed an overall low consumption of large mammals by Apennine bears consistently between sexes, with highest values in spring followed by early summer but null in the other seasons. We also confirmed that consumption of fleshy fruits peaked in late summer, when wild predominated over cultivated fleshy fruits, even though the latter tended to be consumed in higher proportion in autumn. Male bears had higher δ 15N values than females in spring and autumn. Our findings also hint at additional differences in the assimilated diet between sexes, with females likely consuming more herbs during spring, ants during early summer, and hard mast during fall compared to males. In addition, although effect sizes were small and credibility intervals overlapped considerably, management bears on average were 0.9‰ lower in δ 13C and 2.9‰ higher in δ 15N compared to non-management bears, with differences in isotopic values between the two bear categories peaking in autumn. While non-management bears consumed more herbs, wild fleshy fruits, and hard mast, management bears tended to consume higher proportions of cultivated fruits, ants, and large mammals, possibly including livestock. Although multi-year sampling and larger sample sizes are needed to support our findings, our application confirms that SIA can effectively integrate previous knowledge and be efficiently conducted using samples non-invasively collected during population surveys.

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Testing foraging optimization models in brown bears: Time for a paradigm shift in nutritional ecology?

Mikkelsen,

Hobson,

Sergiel

et al. 2023

Ecology

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How organisms obtain energy to survive and reproduce is fundamental to ecology, yet researchers use theoretical concepts represented by simplified models to estimate diet and predict community interactions. Such simplistic models can sometimes limit our understanding of ecological principles. We used a polyphagous species with a wide distribution, the brown bear (Ursus arctos), to illustrate how disparate theoretical frameworks in ecology can affect conclusions regarding ecological communities. We used stable isotope measurements (δ13C, δ15N) from hairs of individually monitored bears in Sweden and Bayesian mixing models to estimate dietary proportions of ants, moose, and three berry species to compare with other brown bear populations. We also developed three hypotheses based on predominant foraging literature, and then compared predicted diets to field estimates. Our three models assumed (1) bears forage to optimize caloric efficiency (optimum foraging model), predicting bears predominately eat berries (~70% of diet) and opportunistically feed on moose (Alces alces) and ants (Formica spp. and Camponotus spp; ~15% each); (2) bears maximize meat intake (maximizing fitness model), predicting a diet of 35%–50% moose, followed by ants (~30%), and berries (~15%); (3) bears forage to optimize macronutrient balance (macronutrient model), predicting a diet of ~22% (dry weight) or 17% metabolizable energy from proteins, with the rest made up of carbohydrates and lipids (~49% and 29% dry matter or 53% and 30% metabolizable energy, respectively). Bears primarily consumed bilberries (Vaccinium myrtillus; 50%–55%), followed by lingonberries (V. vitis‐idaea; 22%–30%), crowberries (Empetrum nigrum; 8%–15%), ants (5%–8%), and moose (3%–4%). Dry matter dietary protein was lower than predicted by the maximizing fitness model and the macronutrient balancing model, but protein made up a larger proportion of the metabolizable energy than predicted. While diets most closely resembled predictions from optimal foraging theory, none of the foraging hypotheses fully described the relationship between foraging and ecological niches in brown bears. Acknowledging and broadening models based on foraging theories is more likely to foster novel discoveries and insights into the role of polyphagous species in ecosystems and we encourage this approach.

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Hair Growth in Brown Bears and Its Application to Ecological Studies on Wild Bears

Cited by 10 publications

References 28 publications

Diet selection and asocial learning: Natal habitat influence on lifelong foraging strategies in solitary large mammals

Diet selection and asocial learning: Natal habitat influence on lifelong foraging strategies in solitary large mammals

Gaining insight into the assimilated diet of small bear populations by stable isotope analysis

Testing foraging optimization models in brown bears: Time for a paradigm shift in nutritional ecology?

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