陕西凤县驯养林麝的种群动态、性比和年龄结构

林麝是濒危资源动物,林麝驯养是保育濒危林麝资源及可持续利用麝香的有效方式。基于对2001至2012年间的陕西凤县林麝驯养的监测和调查,分析了其种群动态、性比和年龄结构。结果表明,陕西凤县的林麝驯养在近10余年获得了快速发展,全县共有150余个麝场,麝场数呈指数式增长,增长率达27.33%,但其平均驯养规模无明显增长,平均存栏种群仅为16.38头。凤县的驯养麝种群总体增长近似指数式增长,增长率达27.22%,目前存栏种群已达3712头。区分性别和年龄,各亚群的增长均呈指数式增长,幼年麝的增长率(30.30%)高于成年麝(27.16%),雄麝的增长率(28.30%)高于雌麝(27.78%)。在2001至2012年间,幼麝种群的雌雄性比((102.64±3.15)%,n=12)和成年麝种群的雌雄性比((100.85±2.585)%,n=10)均显著偏雌(P0.01),但幼麝、成年麝种群间的性比差异不显著(P0.05)。在2005年及2010—2012年间,幼麝(0.5岁龄)占种群的比例为31.91%,亚成体麝(1.5岁龄)占种群的比例为21.11%,成麝(2.5—12.5岁龄)比例为42.72%,老年麝(13.5岁龄及以上)仅占种群的4.26%。合并年龄分析,育龄前个体(幼麝和亚成体麝)的平均比例为53.02%,表明凤县驯养林麝属快速增长种群,其增长潜力较大。在林麝驯养实践中,管理部门可制定准入制度或适当重组现有麝场,促进较大的驯养种群构建,并建立通畅的麝香交易渠道,控制林麝种源的过热交易,以利于林麝驯养种群的性比平衡及可持续的繁育、增长。     

陕西省林麝驯养分布、种群动态及疾病发生

作为濒危麝类动物(Moschus spp.)迁地保育及麝香生产的重要方式,我国的麝类驯养开始于1958年,林麝(M.berezovskii)是最主要的驯养麝种,陕西是我国林麝驯养的重点省份。对陕西2001—2012年的麝类驯养进行监测和分析,结果表明:陕西省林麝驯养在空间上分布极不均匀,其麝场多分布在野生林麝的核心分布区,即秦巴山区的安康、汉中和宝鸡地区,存栏林麝种群达4725头,其种群增长近似指数式增长,种群增长率高达25.06%。此外,全省的麝场数近10年增加较快,年均增长率高达27.92%,但麝场驯养规模却呈下降趋势,2005、2010年全省的麝场平均存栏种群分别为20.53和19.45头。驯养林麝的易发疾病有10类53种,消化道疾病、寄生虫病及呼吸系统疾病为易发疾病。陕西林麝驯养中存在偏雄性死亡,在疾病致死病例中的雄麝(54.28%)显著高于雌麝(45.72%)(P0.05)。此外,因病死亡比例在各年龄组的分布不均匀,成体比例(35.99%)显著高于亚成体(31.86%)(P0.01)和幼体(32.15%)(P0.05),而后二者间差异不显著(P0.05)。为实现陕西林麝的迁地保育和麝香的可持续供给,需大力提高驯养林麝种群的增长率,并加强其疾病防控。     

哺乳期幼麝的摄食时间分配研究

采用所有事件取样法对哺乳期林麝Moschus berezorskii幼体的摄食时间分配进行研究.结果 表明,幼麝吮乳时间随周龄的增加而减少,取食固体饲料(青饲料和混合饲料)的摄食时间随周龄的增加而增加.1月龄中,吮乳时间占总摄食时间的90.8%,青饲料占9.2%.2月龄和3月龄中,幼麝取食固体饲料时间分别占总摄食时间的84.7%和94.9%,吮乳时间分别占15.3%和5.1%.哺乳期雌性幼麝取食母乳、山芋藤和桑叶的时间明显高于雄性幼麝(P＜0.05),而取食精饲料、苦荬菜时间与雄性幼麝无明显差异(P＞0.05);单胎幼麝吮乳、取食山芋藤时间明显高于双胎幼麝(P＜0.05);而取食精饲料、苦荬菜时间明显低于双胎幼麝(P＜0.05),两者取食桑叶时间差异性不显著(P＞0.05).幼麝的摄食时间分配表明,母乳是1月龄幼麝的主要食物成分;2月龄以后,幼麝大量取食固体饲料,母乳在食物组成中退居次要作用.幼麝间吮乳时间的差异反映了不同个体间营养状况的差异.     

圈养大熊猫种群性比失衡现象产生机制的探究

大熊猫(Ailuropoda melanoleuca)的迁地保护工作已开展了近70年,基本实现了圈养种群的自我维持。根据2019年大熊猫谱系,现存圈养大熊猫种群(n=612)的总性比为1.22∶1 (♀336/♂276),与1∶1的性比有显著性差异(P=0.015),目前尚未开展性比失衡现象产生机制的探究工作。本研究以全国最大的圈养大熊猫种群为研究对象,梳理了该种群36年的出生性比、11年的分年龄雌雄个体数量和分年龄死亡雌雄个体数量,计算了出生性比和预期寿命等数据,旨在探究性比失衡的内在原因。结果显示,圈养大熊猫种群的出生性比为1.01∶1,与1∶1的性比无显著性差异(P=0.926);雄性大熊猫在幼年阶段死亡的比例高于雌性(♀38.24%/♂48.72%);圈养大熊猫的出生预期寿命中位数为21.4岁,其中雌性为23.5岁,雄性为19.8岁,雌性预期寿命比雄性长3.7岁。研究表明,圈养大熊猫种群性比失衡的内在原因是雄性大熊猫幼年阶段的死亡比例高于雌性,且雌性大熊猫预期寿命更长。本研究聚焦圈养大熊猫种群的性比失衡问题,首次计算了圈养大熊猫的预期寿命,可为圈养大熊猫种群的饲养管理和野外大熊...     

圈养林麝幼仔的时间分配和行为发育

林麝幼仔的躺卧时间随周龄而减少(R = 01870, P <0101) , 运动时间则相反(R = 01906,P < 0105)。7 周龄后幼麝采食青料的时间明显延长。蹭尾行为和上树行为是林麝的特有行为, 4周龄始出现, 蹭尾行为发生在母仔之间, 可能在母幼通讯中起重要作用, 而幼麝的上树行为是一种戏耍行为。     

圈养雄性林麝(Moschus berezovskii)维持社会等级的冲突行为模式

为了解圈养雄性林麝维持社会等级的冲突行为模式,于2016年6月1日至7月28日在四川马尔康林麝繁育中心,采用行为取样法对14只圈养雄麝进行了防御、追击、取代、进攻及威胁等社会冲突行为取样,分析了圈养雄性林麝社会等级与其发出(接受)的冲突行为类型和表达强度之间的关系。结果表明:林麝雄性圈养群发育了稳定的社会等级结构,作为冲突行为发起者,雄麝均有防御行为和侵犯行为(追击、取代、进攻和威胁)的表达,其防御行为的表达频次(7.71±2.18,n=14)显著高于追击(1.29±0.50,n=14)(P0.05)、取代(1.36±0.57,n=14)(P0.05)、进攻(0.21±0.15,n=14)(P0.05)和威胁(1.29±0.77,n=14)(P0.05) 4种侵犯行为的表达频次;防御行为表达频次与其社会等级呈显著负相关(P0.05);不同序位雄性发出的侵犯行为类型不同,高序位雄麝的高强度侵犯行为(追击和进攻)和低强度侵犯行为(取代和威胁)均有表达,低序位雄麝缺失高强度侵犯行为,仅表达取代行为;作为冲突行为的接受者,雄麝接受的取代行为频次(1.43±0.53,n=14)显著高于进攻(0.29±0.12,n=14)(P0.05)和威胁(0.36±0.16,n=14)(P0.05);中等序位雄麝接受侵犯行为的频次(5.50±1.50,n=2)有高于低序位雄麝(4.60±2.088,n=5)和高序位雄麝(1.14±0.55,n=7)的趋势(P0.05)。由此得出,圈养林麝社群主要通过展现较低强度的侵犯行为维持其社会等级结构,冲突行为的发起者多是序位较高的雄麝,其高强度侵犯行为的表达频次也相对较多。     

驯养林麝泌香生理反应时间与年龄、地域分布的关系

以3处不同地域驯养林麝种群为研究对象,采用分层随机抽样法对四川某麝场61只林麝(离散型年龄分布群)、陕西安康某麝场23只和凤县某麝场5只成体麝(>2岁)泌香期不同生理阶段持续时间、主要气候因子及产香状况等进行观测、记录、统计分析。研究显示陕西、四川驯养种群泌香生理反应均存在2个泌香高峰期,安康驯养种群泌香高峰期集中于5月初和5月底,以5月底频发,四川则出现在6月初和6月下旬,以6月初频发,且5岁前随着年龄的增长,泌香反应集中且明显,此后随年龄增长而趋于平缓,四川驯养种群泌香启动时间较陕西晚1个月左右,两者泌香高频发期接近且两地麝群泌香生理反应主要在40d内完成;四川麝群不同年龄林麝泌香生理反应初期、盛期、后期及总持续时间无显著性差异(P>0.05),合并育成组和成年组仅麝群在泌香后期组间有显著差异;安康、四川两地麝群仅泌香后期持续时间差异显著(P<0.05);麝群中存在11.48%的个体在泌香季节出现2次泌香生理反应现象,但其麝香产量相对较低、且集中于8—9岁以上雄麝,麝群空香率9.8%左右,主要集中于9岁以上雄麝个体;麝群低产麝(产香量≤10g)占18.93%,中产...     

迁地保育林麝体况及影响因素

通过建立基于外貌性状的量化性体况评分标准,于2012年7—10月间对四川马尔康麝场的586头圈养林麝(雌麝299头,雄麝287头)进行了体况评分,并分析了相关变量对林麝体况得分的效应,结果表明:马尔康麝场圈养林麝的体况评分均值为3.49(±0.02,n=586),大部分林麝(59.56%,n=349)的体况评分高于均值。雌麝体况评分均值(3.50±0.02,n=299)略高于雄麝(3.49±0.03,n=287)(P0.05),成体麝体况评分(3.59±0.02,n=291)极显著地高于老龄林麝(3.38±0.09,n=27)和亚成林麝(3.35±0.03,n=184)(P0.01)。林麝的体况得分与其年龄相关不显著(r=0.07,P0.05),但亚成体及成体麝的体况评分与其年龄间的相关极显著(亚成体r=0.19,P0.01;成体r=-0.16,P0.01),而老龄麝体况评分与其年龄略呈负相关(r=-0.23,P0.05)。S模型y=e1.2811-0.0885/a(R2=0.051,df=500,F=26.74,P0.01)可近似拟合林麝体况得分和年龄的关系。此外,马尔康麝场泥地基底的改装圈舍中的林麝体况(3.52±0.03,n=197)显著优于原装青砖圈舍林麝评分(3.47±0.02,n=389)(P0.05)。     

迁地保育林麝的侵犯性、等级序位及相互关系

侵犯性是动物个性的重要维度之一,体现了其主动挑衅和攻击其他个体的倾向。动物的侵犯性与其社会结构及等级序位存在紧密关系。本研究于2018年6月1日至7月31日对四川马尔康林麝繁育场的圈养林麝(Moschus berezovskii)进行了行为取样,计算林麝个体的侵犯性个性(侵犯性指数)和等级序位指数,分析圈养林麝的侵犯性和等级序位格局、影响因素及相互关系。结果表明,圈养林麝的侵犯性在性别间存在显著差异,雄性林麝的侵犯性(0.45±0.09,n=22)显著高于雌性(0.22±0.06,n=30)(P 0.05),年龄和驯养密度对其侵犯性的效应均不显著(P 0.05),说明林麝侵犯性的刚性较强;圈养林麝等级序位的性别间差异不显著(P 0.05),亚成体麝与成体麝的等级序位差异也未达显著水平(P 0.05),原因在于麝场的建群未区分年龄组;圈养林麝个体的侵犯性与其等级序位显著正相关,林麝个体的侵犯性越大,其等级序位越高(r=0.73,P 0.05),推测这与社群的序位等级构建和资源竞争有关。     

四川马尔康圈养林麝的刻板行为

在圈养环境下,迁地保育野生动物易发育刻板行为,刻板行为的发育可直接影响圈养野生动物的繁殖和存活,从而影响迁地保育。2016年5月1日至7月31日间,采用焦点取样及所有事件记录法对四川马尔康林麝繁育场的75头圈养林麝(Moschus berezovskii)进行了刻板行为取样,分析了性别、年龄、圈区环境、圈群结构等因素对其刻板行为的效应。结果表明,四川马尔康麝场的圈养林麝在单位取样时间(10 min)内展现的刻板行为持续时间占比为20.53%±2.43%(n=75);雌麝刻板行为持续时间占比(18.14%±3.26%,n=46)略低于雄麝(20.89%±3.98%,n=25);随圈养年限(本研究中的圈养林麝"年龄"即是"被圈养年数")增加,林麝展现刻板行为的持续时间显著增加(P0.05);圈区环境设施对刻板行为存在显著效应(P0.05),裸地基底圈舍中林麝的刻板行为持续时间占比最高(33.11%±6.16%,n=24);圈群结构对林麝刻板行为持续时间的影响不显著(P0.05),混合圈群的刻板行为持续时间(19.31%±3.18%,n=53)最小;圈群密度对刻板行为持续时间的效应不显著(P0.05)。增加圈养环境的植被覆盖,进行混合圈养,可有效降低圈养林麝的刻板行为强度,并可提升林麝迁地保育的有效性。     

Winter fawn survival in black-tailed deer populations affected by hair loss syndrome

Overwinter fawn mortality associated with hair loss syndrome (HLS) is anecdotally thought to be important in declines of Columbian black-tailed deer (Odocoileus hemionus columbianus) populations in Washington and Oregon (USA). We determined prevalence of HLS in black-tailed deer, September and April fawn:doe ratios, and minimum overwinter survival rates of fawns for selected game management units (GMUs) in western Washington from 1999 to 2001. Prevalence of HLS ranged from 6% to 74% in fawns and 4% to 33% in does. Minimum fawn survival ranged from 0.56 to 0.83 and was unrelated to prevalence of HLS in either does (r=0.005, P=0.991) or fawns (r=-0.215, P=0.608). The prevalence of HLS in either does or fawns was also unrelated to either fall fawn:doe ratios (HLS does: r=-0.132, P=0.779; HLS fawns: r=0.130, P=0.760) or spring fawn:doe ratios (HLS does: r=-0.173, P=0.711; HLS fawns: r=-0.020, P=0.963). However, the prevalence of HLS in does and fawns was strongly related (r=0.942, P=0.002), and GMUs with high prevalence of HLS had lower deer population densities (fawns: r=-0.752, P=0.031; does: r=-0.813, P=0.026). Increased overwinter mortality of fawns because of HLS was not supported by our data. Decreased production of fawns, increased summer mortality of fawns, or both were seen in six of eight study GMU-year combinations. Observed rates of productivity and minimum fawn survival were inadequate to maintain population size in five of eight study GMU-year combinations, assuming an annual doe survival rate of 0.75. The influence of deer condition and population health on adult survival, fawn production, preweaning fawn survival, parasitism, and prevalence of HLS in both fawns and adults need to be clarified to identify what factors are limiting black-tailed deer productivity.     

White-Tailed Deer Population Dynamics Following Louisiana Black Bear Recovery

Changing predator communities have been implicated in reduced survival of white-tailed deer (Odocoileus virginianus) fawns. Few studies, however, have used field-based age-specific estimates for survival and fecundity to assess the relative importance of low fawn survival on population growth and harvest potential. We studied white-tailed deer population dynamics on Tensas River National Wildlife Refuge (TRNWR) in Louisiana, USA, where the predator community included bobcats (Lynx rufus), coyotes (Canis latrans), and a restored population of Louisiana black bear (Ursus americanus luteolus). During 2013–2015, we radio-collared and monitored 70 adult (≥2.5 yrs) and 21 yearling (1.5-yr-old) female deer. Annual survival averaged 0.815 (95% CI = 0.734–0.904) for adults and 0.857 (95% CI = 0.720–1.00) for yearlings. We combined these estimates with concurrently collected fawn survival estimates (0.27; 95% CI = 0.185–0.398) to model population trajectories and elasticities. We used estimates of nonhunting survival (annual survival estimated excluding harvest mortality) to project population growth (λ) relative to 4 levels of harvest (0, 10%, 20%, 30%). Finally, we investigated effects of reduced fawn survival on population growth under current management and with elimination of female harvest. Despite substantial fawn predation, the deer population on TRNWR was increasing (λ = 1.06) and could sustain additional female harvest; however, the population was expected to decline at 20% (λ = 0.98) and 30% (λ = 0.94) female harvest. With no female harvest, the population was projected to increase with observed (λ = 1.15) and reduced fawn survival (λ = 1.02), but the population could not sustain current female harvest (10%) if fawn survival declined (λ = 0.90). For all scenarios, adult female survival was the most elastic parameter. Given the importance of adult female survival, the relative predictability in response of adult survival to harvest management, and the difficulty in altering fawn survival, reducing female harvest is likely the most efficient approach to compensate for low fawn survival. On highly productive sites such as ours, reduction, but not necessarily elimination, of harvest can mitigate effects of low fawn survival on population growth. © 2020 The Wildlife Society.     

Survival of White-Tailed Deer Fawns in Southern Illinois

Abstract: Survival of white-tailed deer (Odocoileus virginianus) fawns has been quantified throughout much of North America. However, few studies have assessed the influence of intrinsic factors (e.g., fawn age and birth mass) and habitat on fawn survival. During 2002-2004, we captured and radiocollared 166 fawns in southern Illinois, USA, to estimate survival rates, determine causes of mortality, and identify factors influencing fawn survival. We used a known fates model in program MARK to estimate survival rates and compare explanatory models based on Akaike's Information Criterion corrected for small sample sizes (AIC_c). We developed 2 candidate sets of a priori models to quantify factors influencing fawn survival: model set 1 included intrinsic factors and model set 2 focused on habitat variables. We recorded 64 mortalities and the overall survival rate was 0.59 (95% CI = 0.51-0.68). Predation was the leading source of mortality (64%) and coyotes (Canis latrans) were the most prominent predator. For model set 1, model {S_{age X year}} had the lowest AIC_c value suggesting that the age at mortality varied among capture years. For model set 2, model {S_{landscape+forest}} had the lowest AIC_c value and indicated that areas inhabited by surviving fawns were characterized by a few large (i.e., > 5 ha) irregular forest patches adjacent to several small nonforest patches, and survival areas also contained more edge habitat than mortality areas. Due to the magnitude of coyote predation, survival areas could have represented landscapes where coyotes were less effective at locating and capturing fawns when compared to mortality areas. This study was the first account of macrohabitat characteristics directly influencing fawn survival. Wildlife managers can use this information to determine how habitat management activities may affect deer populations.     

Predator densities and white-tailed deer fawn survival

Predation is the dominant source of mortality for white-tailed deer (Odocoileus virginianus) <6 months old throughout North America. Yet, few white-tailed deer fawn survival studies have occurred in areas with 4 predator species or have considered concurrent densities of deer and predator species. We monitored survival and cause-specific mortality from birth to 6 months for 100 neonatal fawns during 2013–2015 in the Upper Peninsula of Michigan, USA, while simultaneously estimating population densities of deer, American black bear (Ursus americanus), coyote (Canis latrans), bobcat (Lynx rufus), and gray wolf (Canis lupus). We estimated fawn predation risk in response to sex, birth mass, and date of birth. Six-month fawn survival pooled among years was 36%, and fawn mortality risk was not related to birth mass, date of birth, or sex. Estimated mean annual deer and predator densities were 334 fawns/100 km², 25.9 black bear/100 km², 23.8 coyotes/100 km², 3.8 bobcat/100 km², and 2.8 wolves/100 km². Despite lower estimated per-individual kill rates, coyotes and black bears were the leading sources of fawn mortality because they had greater densities relative to bobcats and wolves. Our results indicate that the presence of more predator species in a system is not entirely additive in its effect on fawn survival. © The Wildlife Society, 2019     

Survival of white-tailed deer fawns on Marine Corps Base Quantico

Some jurisdictions in the eastern United States have reduced harvest of white-tailed deer (Odocoileus virginianus) because of perceived declines in recruitment and population size over the last decade. Although the restoration of American black bears (Ursus americanus) and the colonization of coyotes (Canis latrans) have increased fawn predation in some areas, limited information exists on how temporally dynamic resources and weather influence fawn survival. Therefore, we evaluated fawn survival probability, cause specific mortality, and if factors such as oak (Quercus spp.) mast abundance, winter severity, precipitation, and landscape composition influenced mortality risk on Marine Corps Base Quantico in northern Virginia, USA, from 2008 to 2019. We tracked 248 fawns outfitted with very high frequency radio-collars and predation was the leading cause of mortality (n = 42; 45%). We estimated survival to 133 days and survival pooling all years (2008–2019) was 0.50 (95% CI = 0.42–0.60). Increased annual red oak (Quercus spp.) mast abundance from the previous fall reduced mortality hazard for fawns. The longevity of our study revealed a link between fawn survival and a specific maternal resource (red oak mast) only available during gestation. Our results highlight the importance of oak mast in eastern deciduous forests and, more broadly, overwinter maternal condition on white-tailed deer recruitment.     

Increased brown bear predation on sika deer fawns following a deer population irruption in eastern Hokkaido, Japan

By the 1970s, brown bears (Ursus arctos) in Hokkaido, northern Japan, were opportunistic omnivores that mainly depended on plant materials. Because the sika deer (Cervus nippon) population irrupted in eastern Hokkaido in the 1990s, we expected that brown bears might prey on sika deer fawns. First, we developed a simple and cost-effective method of monitoring possible bear predation on deer fawns by analyzing the widths of deer hairs remained in bear scats. Based on hair thickness standards, we distinguished the brown bear consumption of deer fawns from adults by analyzing bear scats (n?=?108) collected during the deer birthing season (late May?Clate July) in 1999?C2008. To evaluate the importance of fawns to bears, we compared the occurrence of fawn and adult deer hairs in bear scats among three periods (I, 1999?C2000; II, 2003?C2005; III, 2006?C2008) in eastern Hokkaido. The occurrence of fawn hairs in bear scats increased from 12.5 to 27.3?% in volume and from 6.3 to 33.6?% in frequency from period I to period III, whereas adult hairs in scats decreased from 42.8 to 26.1?% in volume and from 34.4 to 22.7?% in frequency during the same time. These data suggest that bears increasingly preyed on deer fawns after the deer population irruption and decreasingly used adult carcasses because of the enforcement of deer carcass treatment by the Hokkaido government.     

Early survival in roe deer: causes and consequences of cohort variation in two contrasted populations

Time- and sex-specific summer survival of roe deer fawns was estimated using capture-mark-recapture methods in two enclosed populations living in contrasting conditions. The population of Trois Fontaines (eastern France) was roughly constant in size throughout the study period, while in Chizé (western France), the population experienced frequent summer droughts and numbers decreased continuously during the study. Early survival of fawns was low and highly variable over the years at both Chizé and Trois Fontaines, and demonstrated marked variations between cohorts that need to be taken into account when modelling roe deer population dynamics. In Trois Fontaines, fawn survival was positively correlated with early body growth and total rainfall in May and June. In Chizé, fawn survival decreased with increasing density and tended to increase with increasing rainfall in May and June and adult female body mass. These factors explained more than 75% of the variability in early survival observed in both populations. Variation between cohorts had different consequences for the two populations. At Trois Fontaines, cohort variation was limited to a numerical effect on early survival. However at Chizé, cohort variation was long-lasting and affected the phenotypic quality of survivors at later ages, and thereby future survival and breeding abilities (both numerical and quality effects). Male and female fawns had similar survival over their first summer in both populations. This result contrasts with the lower survival of young males often observed in ungulates. Two ultimate causes can be proposed to account for the low and variable survival of roe deer fawns over the first summer: the high energy expenditures incurred by does during each breeding attempt and/or the low absolute body size of newborn roe deer fawns. Received: 28 April 1997 / Accepted: 14 July 1997     

Forage quality's influence on mule deer fawns

In many mule deer (Odocoileus hemionus) populations, recruitment of fawns drives population dynamics. The quality of food available to females and their fawns in summer and autumn may play an important role in fawn recruitment. We examined direct links between digestible energy (DE) content of food and the DE intake of females on the nutrient concentration of milk and between the nursing behavior, DE intake, growth, and survival in captive mule deer fawns. We offered females and their fawns diets that simulated the natural decline in DE content of forage from mid-summer to late autumn in many western landscapes. Fawns fed a higher DE diet weighed 14% more at the onset of winter, had fewer unsuccessful nursing attempts, consumed milk with more protein and energy, and had higher survival than fawns fed a low DE diet. Differences between fawn performances among treatments were greatest when diet quality began decreasing earlier in the summer. Because our results indicate that summer and autumn nutrition is likely to influence fawn recruitment, wildlife biologists should include metrics for summer precipitation and late autumn fawn mass in population models, and land managers should focus on methods for improving the nutritional carrying capacity of summer and early autumn habitats. © 2011 The Wildlife Society.     

Culling Versus Density Effects in Management of a Deer Population

Abstract: Wildlife managers often manipulate hunting regulations to control deer populations. However, few empirical studies have examined the level of hunting effort (hunter-days) required to limit population growth and demographic effects through harvesting of females. Moreover, the relative importance of density effects on population growth has not been quantified. We reconstructed a sika deer [Cervus nippon] population over a period of 12 years (1990–2001) using age- and sex-specific harvest data. Using cohort analysis, we analyzed population dynamics, focusing on 1) the relationship between hunting effort and hunting-induced mortality rate, 2) relative contributions of hunting mortality and recruitment of yearlings to annual changes in population growth rate, and 3) annual variation in recruitment rate. Population size increased until 1998 and declined thereafter. The population growth rate changed more in response to annual changes in recruitment rate than hunting mortality rate. Temporal variation in recruitment rate was not controlled by birth rate alone; direct density dependence, intensities of hunting mortality for fawns, and for females (≥2 yr of age), which accounted for the fawn survival rate, were required as factors to explain temporal variation. Density effects on the recruitment rate were not strong enough to regulate the population within the study period; high hunting mortality, with intensive female harvesting, was necessary to prevent population growth. Hunting effort was a good predictor of the hunting mortality rate, and female harvest had a negative effect on the recruitment rate through fawn survival. We suggest that >3,500 hunter-days and prioritization of female harvesting are required to prevent increases in this deer population.     

Factors Influencing Survival Rates of Pronghorn Fawns in Idaho

Pronghorn (Antilocapra americana) occur throughout western North America. In Idaho, USA, following intensive hunting to reduce crop depredations in the late 1980s, pronghorn populations have not rebounded to desired levels. Because neonatal survival in ungulates is one factor limiting population growth, we evaluated cause-specific mortality and the influence of intrinsic and extrinsic factors on survival rates of 217 radio-collared pronghorn fawns across 3 study areas in Idaho during 2015–2016. For intrinsic variables, we determined the sex and body mass index (BMI) for each fawn. For extrinsic variables, we determined the abundance of predators and alternate prey, estimated the normalized difference vegetation index (NDVI) for 1 month pre- and post-parturition, and measured fecal nitrogen and diaminopimelic acid (DAPA). We considered NDVI as a measure of plant productivity, and fecal nitrogen and DAPA as possible proxies of diet quality. We predicted NDVI, fecal nitrogen, and DAPA would be positively related to the nutritional status of females and positively related to fawn survival. We used Program MARK with known fate models to estimate semi-monthly survival rates of pronghorn fawns for the first 4 months post-parturition. During both years, the leading cause of fawn mortality was coyote (Canis latrans) predation (58%), followed by unknown causes of mortality (18%), unknown predation (12%), predation by bobcats (Lynx rufus; 6%), predation by golden eagles (Aquila chrysaetos; 3%), and other (3%). Mean fawn survival for the 4 months post-parturition across years and study sites was 0.42 ± 0.04 (SE; range = 28–62%). The top survival model included BMI, lagomorph abundance, and DAPA and had a model weight of 83.3%. All 3 variables were positively related to pronghorn fawn survival. Because females with increased nutrition generally have heavier fawns, BMI was likely correlated to diet quality, which was supported by the positive relationship between DAPA and fawn survival. We hypothesize that high lagomorph abundance created an alternate prey base to buffer coyotes from preying on pronghorn neonates. We found no influence of measures of NDVI (pre- and post-parturition), fecal nitrogen, or predator abundance on fawn survival. Management actions providing high-quality forage for pronghorn are likely to contribute to production of heavier fawns having the highest chance of survival. © 2020 The Wildlife Society.