鄱阳湖稻田生境中越冬灰鹤行为模式及其影响因素

2018年10月—2019年3月,采用焦点动物法研究了鄱阳湖区稻田生境中灰鹤(Grus grus)越冬期的行为模式及其影响因素。结果表明:越冬期灰鹤的主要行为是觅食(77.45%)、警戒(11.17%)和修整(7.82%);行为模式以取食-警戒-取食或取食-修整-取食为主;幼鹤取食行为的时间分配和持续时间均极显著高于成鹤(P0.01),推测幼鹤取食效率低,单次取食持续时间和总时间较长;成鹤警戒行为(P0.01)极显著高于幼鹤,成、幼鹤警戒行为的持续时间无显著差异,取食间隔的警戒频次和时间分配均显著高于幼鹤(P0.05),说明成鹤是通过增加警戒次数来确保幼鹤的安全;取食行为的持续时间和时间分配在整个越冬期均显著升高,取食间隔期间的行走行为也逐渐上升,这与食物资源的可获得性有关;建议适当降低家鸭放牧等人类活动,减少灰鹤越冬期的取食难度;灰鹤不同家庭群的行走行为和取食间隔的行走行为均有显著性差异,推测与各家庭群占有的食物资源质量相关;行为节律上,灰鹤各时段取食行为占总行为的比例均较高,在10:00—10:59、12:00—12:59和16:00—16:59出现取食小高峰;警戒行为保持在一个稳定水平,修整行为高峰出现在取食行为高峰之后,这是因为灰鹤保持取食行为积累疲劳后进行修整;成鹤的取食行为节律性较幼鹤明显,幼鹤的取食行为曲线随机性强,这与幼鹤取食经验不足有关;幼鹤警戒行为的高峰出现在成鹤警戒的低谷,推测与保持整个家庭群较高的总体警戒水平有关。     

云南纳帕海越冬黑颈鹤日间行为模式与年龄和集群的关系

2006年10月—2007年5月,在云南省西北部纳帕海,采用路线调查结合瞬时扫描行为取样法,对越冬黑颈鹤(Grus nigricollis)种群的时间分配及其与年龄、集群和时间的关系进行了观察。结果说明,黑颈鹤越冬活动主要是以觅食为主,占日间时间的(76.81±9.1)％。越冬期间黑颈鹤日间行为的节律性较为明显,具有适应高寒气候的特点。集群形式对成鹤的行为有着显著影响,集群和家庭中活动的成鹤在觅食、警戒和争斗中存在显著差异(F1,76= 0.27、0.77, U= 279, P= 0.001—0.000)。年龄是影响鹤群行为的因素之一。幼鹤相比成鹤有较多的觅食时间和休息时间,警戒行为比例较低(F1,76= 0.04—2.59, U= 188—299, P= 0.006—0.000),且不受集群形式的影响。随着越冬期间的早、中、晚3个时期的环境变化,黑颈鹤的时间分配有显著变化(F2,36= 4.63—26.54, 22= 5.29—13.68, P= 0.0016—0.000)。不同越冬地的黑颈鹤行为存在差异。气候、食物资源和人为影响可能是造成这些差异的主要因素。     

农业耕作活动对西藏越冬黑颈鹤食性及食物可获得性的影响

于1996年1月对西藏中南部越冬黑颈鹤的食性和谷物性食物的可获得性进行了研究。青梨（Hordeum vulgare),春小麦（Triticum spp.),冬小麦（Triticum spp.)是该地区的3种主要作物。对黑颈鹤粪便的分析表明,越冬黑颈鹤取食大量的农作物,尤其是小麦散落从粒,而冬小麦苗仅上鹤类食物组成的很小一部分。秋收后的翻耕,放牧等农业活动影响地面上作物残物（种子,叶,秆或根）及谷粒残物（裸粒,穗稃）的数量,农地翻耕掩埋了大部分的作物残物。未翻耕青梨地与小麦地上的作物残物覆盖比值相似。谷物残物的密度在未翻耕的小麦地上最大,为了最大限度地增加黑颈鹤的冬季食物来源,减少人为活动对黑颈鹤的干扰,我们建议：在秋收后不要翻耕河流两侧的青梨地和小麦地;在冬小麦种植地区,冬小麦应仅仅种植在主要公路两侧。     

鄱阳湖滨藕塘生境中白鹤取食行为研究

2016年12月—2017年2月和2017年12月—2018年1月,采用焦点动物法对鄱阳湖滨藕塘生境中白鹤(Grus leucogeranus)的取食行为进行观察,共记录921只次成鹤和547只次幼鹤的取食行为。结果表明,白鹤栖息水深为(17.29±8.75)cm(n=1468),取食水深为(18.84±10.32)cm(n=600),单次取食持续时间为(3.10±1.69)s(n=600),取食频次为(12.24±3.89)次/min(n=1012),取食成功频次为(1.78±1.59)次/min(n=1468),取食成功率为(16.26±14.41)%(n=1012)。成鹤取食成功频次(SymbolcA@~2=70.797,df=1,P=0.000)和取食成功率(SymbolcA@~2=5.356,df=1,P=0.020)均显著高于幼鹤,表明成鹤取食能力较幼鹤强,成鹤可以获得更多的能量。成鹤除维持自身能量支出外,还需要花费较多的能量用于辅食和警戒行为。成幼鹤的取食频次和单次取食持续时间无显著差异,这与成幼鹤的体型大小、能量需求和体内氧气储存量类似有关,也与多数研究认为幼鹤觅食经验不足,觅食成功率低,需要靠多次取食来补偿能量的观点不同。成鹤取食水深极显著高于幼鹤(SymbolcA@~2=50.945,df=1,P0.0001),这可能与体型和取食经验有关。不同栖息水深下白鹤的取食成功率(SymbolcA@~2=15.297,df=4,P=0.004)和取食成功频次(SymbolcA@~2=23.155,df=4,P0.0001)均存在极显著差异。不同时段的取食频次、取食成功频次和取食成功率均无显著差异,这可能与藕塘生境中白鹤采取触觉取食有关。此外,白鹤昼间取食行为无明显节律性,因此昼间能量需求相似,取食参数没有显著差异。     

西藏拉萨越冬黑颈鹤家庭群的警戒同步性

以往关于动物警戒行为的研究多以经典随机独立模型为基础,然而,近期一些理论和实证研究则向该模型发出了挑战。根据警戒行为同步性程度的不同,集体警戒可能存在基于模仿的同步警戒和避免重复的协调警戒两种模式。研究了中国雅鲁藏布江自然保护区越冬黑颈鹤家庭群的警戒行为,通过独立样本t检验验证由于年龄和是否携幼所导致的个体警戒水平的差异,通过单因素方差分析比较不同类型家庭群的集体警戒水平,通过配对t检验比较集体警戒的实际观测值和独立假设下的预期值从而确定越冬黑颈鹤家庭群的警戒同步性。结果表明家庭群中的幼年黑颈鹤警戒行为时间显著低于成年黑颈鹤,但幼鹤的存在对成鹤的警戒水平没有显著影响。不同类型黑颈鹤家庭群的集体警戒水平没有差异,但并未如预期表现为同步警戒。警戒行为模式是动物在特定环境中的适应性表现,越冬黑颈鹤生境中不存在落后目标策略的捕食者和高强度的捕食风险,因而可能不足以诱发以降低捕食风险为主要功能的高强度的警戒行为同步性;同时,在资源匮乏的冬季对食物获取的优先性可能也削弱了对同步警戒的需求。     

野生藏酋猴冬季食物组成及营养成分

觅食是获取营养物质和能量的重要途经。对于栖息在四季分明地区的灵长类动物而言,低温以及食物资源相对匮乏的冬季是其生存和生长发育的瓶颈期。本研究以安徽黄山的野生藏酋猴（Macaca thibetana）天湖山群为对象,于2019年11月至2020年1月采用瞬时扫描取样法（Instantaneous scan sampling）采集猴群觅食行为数据,并分析其冬季食物组成及食物中各化学成分含量对取食的影响。结果显示,野生藏酋猴在冬季共取食23科31属34种植物,主要包括壳斗科（Fagaceae,21.62%）、樟科（Lauraceae,17.57%）、蔷薇科（Rosaceae,8.11%）的植物,取食部位以叶片（66.22%）和果实（种子）（24.32%）为主。不同取食部位的水分、总糖、淀粉、脂肪、单宁等成分存在显著差异。其中,叶片的水分含量高于果实（种子）、茎和芽,茎和果实（种子）含有较高的总糖,果实（种子）的淀粉和脂肪含量最高,芽的单宁含量最高。此外,取食植物中的总糖含量高于非取食植物。结果表明,野生藏酋猴适应寒冷冬季与食物匮乏的觅食策略是对植物种类、植物部位及其主要营养成分的综合结果。     

云南省纳帕海自然保护区越冬黑颈鹤的集群特征

2004年10月-2005年5月,在云南纳帕海自然保护区采用定点扫描法对越冬黑颈鹤(Grus nigricollis)的集群类犁和集群大小进行了观察.结果表明黑颈鹤夜间集群夜栖,形成较大的夜栖群,平均群体大小为67.9只(16-157,n=17):按照有无灰鹤加入,又将其分为同种集群和混种集群两种类型,其中同种集群的黑颈鹤数量占整个越冬种群的65.3%.在白昼,黑颈鹤以家庭鹤、集群鹤及特殊群体3种类型活动,家庭鹤和集群鹤的平均大小分别为2.7只(2-4,n=145)和16.1只(3-65,n=1017).黑颈鹤的集群大小并不稳定,在日内和月份间均有明显变化(P=0.000＜0.05).存越冬期,最大集群形成于12月,其次为11月和1月;在日内,早上8时集群最大,随后减小并保持相对稳定,18时黑颈鹤开始向夜栖地靠拢,使得集群再次开始增大.随后观察中还发现,黑颈鹤的家庭解体过程开始于3月底,当幼鹤被成鹤驱逐离群后,逐渐加入集群鹤活动,从而使得家庭鹤和集群鹤的大小和组成发生改变.黑颈鹤的集群大小和组成受自身状况、种内关系、天气、食物等多种因素的共同影响,随时间和季节变动而发生变化,是对自身、种群和环境条件变化的综合反映.     

黑颈鹤种群动态模型

本研究据已收集到的数据,用非参数统计方法确定了黑颈鹤种群的性比为1:1,避免了大量取样。根据黑颈鹤的特点,我们将其种群分成4个年龄组,并求出了各年龄组的存活率和繁殖率,据此建立了描述黑颈鹤种群动态的数学模型。用模型计算得出在乌蒙山区越冬的黑颈鹤种群的自然增长率为1.85‰;理想的种群结构为幼鹤、亚成鹤、成鹤、老鹤分别占总数的15.5％、21.5％、60.2％、2.8％,最后预测了乌蒙山黑颈鹤种群在1988～2000年越冬期的数量。1989年1月经实地调查该种群总数为310只,而预测值为303只,误差约2％。     

鄱阳湖围垦区藕塘越冬白鹤的时间分配与行为节律

2016年12月—2017年3月,采用瞬时扫描法研究了鄱阳湖围垦区藕塘生境中白鹤Grus leucogeranus越冬期的行为,共扫描2560次,23219只次,包括18031只次成鹤和5188只次幼鹤。结果表明,觅食(41.78%)、警戒(25.02%)、修整(15.00%)和休息(10.84%)是白鹤越冬期的主要行为。与自然生境相比,藕塘生境中白鹤主要采取多休息和修整的策略来节省能量支出。成鹤的觅食行为(35.29%)显著低于幼鹤(62.42%)(F_(1,12)=45.977,P0.01),警戒行为(28.66%)则显著高于幼鹤(10.26%)(F_(1,12)=38.975,P0.01)。家庭群成鹤觅食行为(43.96%)极显著高于非家庭群成鹤(27.04%)(F_(1,12)=60.169,P0.01)。家庭群成鹤需要喂食幼鹤,它们花费更多的时间觅食弥补能量的消耗。行为节律上,白鹤各时段觅食行为占总行为的比例均较高,11:00—11:59出现明显高峰,占总行为的48.64%。警戒行为无明显的低谷和高峰。成鹤在各时段的觅食行为比例均明显低于幼鹤,成鹤和幼鹤的觅食曲线变化趋势相似,即觅食比例的升高和降低比较同步。成鹤在各时段的警戒行为和修整行为比例均明显高于幼鹤,成幼鹤的休息行为比例在各时段差别不大,均在14:00—14:59有个明显的高峰。家庭群成鹤的觅食行为比例几乎在各时段均明显高于非家庭群,家庭群成鹤的修整行为和休息行为在大部分时段均低于非家庭群成鹤。因此家庭群成鹤采取多取食,少休息和修整的策略提高自身的适合度,同时保证对后代的抚育。     

云南大山包黑颈鹤日间越冬时间分配和活动节律

2006年10月—2007年4月采用瞬时扫描取样法对云南省昭通市大山包黑颈鹤国家级自然保护区内越冬的黑颈鹤(Grus nigricollis)种群进行了越冬时间分配和日间活动节律的研究。取食是黑颈鹤越冬期间最主要的行为,占(53.05±4.93)%,其次为警戒(18.75±2.65)%、搜寻(10.38±1.34)%和休整(10.32±4.93)%,其余行为依次为:行走(4.90±1.59)%、飞行(1.70±0.38)%、其他(0.55±0.41)%、争斗(0.36±0.25)%。黑颈鹤的出飞时间与日出时间、飞回时间与日落时间分别具有显著的正相关和负相关关系。越冬期间黑颈鹤日间各时间段(1h)(09:00—18:00)和各月份间(2006.11—2007.03)行为差异极显著(P<0.05),并呈现出上午和下午取食双峰、中午休息高峰的规律性变化。气温高时黑颈鹤增加休整时间减少取食时间;气温低时则减少休整时间增加取食时间。偏相关分析说明:环境温度独立地对越冬时间分配产生影响,湿度通过温度对黑颈鹤越冬时间分配产生相反的影响。     

Foraging strategy in a subterranean rodent,Spalax ehrenbergi: a test case for optimal foraging theory

Summary The foraging behavior of the subterranean mole rat Spalax ehrenbergi (Rodentia, Spalacidae) was tested according to the framework of optimal foraging theory. We compared the frequencies of food species hoarded in storage chambers of mole rats with the frequencies of these species occurring in the vicinity of the mole rats' nest mounds during the winter and spring seasons. In addition, we examined the food composition of several summer nest mounds. Laboratory observations were conducted in order to test the foraging behavior of mole rats under simulated subterranean conditions. The mole rat is a generalist and collects a variety of food species. Out of 33 plant species that were hoarded by mole rats in the 21 studied nest mounds, 61% (n=20) were geophytes, 21% (n=7) perennial herbs, 15% (n=5) annual herbs and 3% (n=1) dwarf shrubs. The frequency of each collected species in the 16 winter and spring nest mounds is in general accordance with its frequency in the mole rat's territory. This implies that the mole rat randomly samples the food reserve of its territory without special preference or directed search for a particular species. The collection or avoidance of any food item is not dependent on the presence or absence of any other food item. We suggest that the foragin generalism of the mole rat is a product of the constraints of a subterranean niche — the necessity to hoard food as much as possible in a limited time period and the high energetic investment of tunneling to the food items.     

Spatial clumping of food and social dominance affect interference competition among ruddy turnstones

In studying the success of foraging animals, studies of interferencecompetition have put emphasis on effects of competitor density,whereas studies of resource defense have focused on the effectsof the spatial distribution of food within patches. Very fewstudies have looked at both factors simultaneously, that is,determined whether the effects of competitor density on foragingsuccess depend on the spatial distribution of food. We studiedthe behavior and the foraging success of ruddy turnstones (Arenariainterpres) using an experiment in which we varied both the presenceof a competitor and the food distribution. Because turnstonesmay differ strongly in their relative dominance status, we alsoexperimentally varied the foragers' relative dominance status.We found that the presence of a competitor only reduced theforaging success of subordinate birds foraging at the clumpedfood distribution. At this condition, dominant and subordinatebirds differed markedly in their foraging success. Contraryto our expectations, we did not observe more agonistic behaviorat the clumped food distribution. This indicates that the amountof agonistic behavior observed may be a bad indicator of interferenceeffects. These findings have specific implications for modelsof interference competition. Most notably they show that theeffects of competitor density on agonistic behavior and foragingsuccess may well depend on the spatial distribution of foodand the foragers' relative dominance status. Additionally, ourresults suggest that social dominance will not be fully understoodwithout considering long-term processes such as the formationand maintenance of social dominance hierarchies.     

The Consequences of Predation Risk on the Male Territorial Behavior in a Solitary Bee

Territorial males may adopt a mating tactic that yields greater reproductive success but that at the same time increases the risk of predation. Plasticity in reproductive behavior can reflect a balance between sexual selection and natural selection. In this study, we sought to verify the effect of predation risk on territorial behavior of males of the solitary bee Ptilothrix fructifera (Apidae). Males of the species employ alternative mating tactics and can be territorial in defense of larval food sources. By manipulating predator models in the field, we tested whether (1) males avoid perch flowers containing predator models; (2) males alternate between mating tactics when their territory is associated with a predation risk; and (3) female foraging on flowers in a territory is altered in the presence of a predator model. We measured the responses of males and females in flowers containing and not containing a model of a spider or a stuffed bird. The results show that territorial males of P. fructifera alter their territorial behavior when faced with a high risk of predation. They do not abandon their territory or change to a non‐territorial mating tactic, but instead change the use of their territory, avoiding flowers containing predator models or perching on other flowers when the previous flower presented a potential predation risk. Female P. fructifera decreases the frequency of their visits to flowers and the length of time spent there in the presence of a spider model. In short, in the face of predation risk, females and males alter their behaviors at the cost of less efficient foraging and searching for partners, respectively.     

Social behavior of juvenile chum salmon, Oncorhynchus keta, under risk of predation: the influence of food distribution

Synopsis Social interactions can influence both foraging reward and vulnerability to predators. We examined social interactions in groups of juvenile chum salmon, Oncorhynchus keta, receiving food that was either spatially dispersed, with many food items appearing synchronously, or spatially clumped, with individual food items appearing asynchronously. These experiments were conducted both in the presence and absence of predators. when food was dispersed and predators were absent, juvenile chum formed schools and all individuals had access to food, despite frequent agonistic interactions. When predators were present, schooling and feeding continued, but agonistic interactions ceased. In contrast, when food was clumped, dominant fish utilized aggression to monopolize food regardless of whether predators were present or absent, resulting in decreased group cohesion. These results illustrate that food distribution and social interaction may play a role in determining how fish balance predation risk against foraging reward.     

Why are shrews so small? The costs and benefits of small size in northern temperateSorex species in the context of foraging habits and prey supply

This paper reviews the ecological advantages and disadvantages of very small body size inSorex Linnaeus, 1758 shrews living at high latitudes with cold winters. It examines the feeding and foraging habits of small and large shrews in the context of prey supply, location of winter prey sources, territory requirements, habitat exploitation and inter-specific competition. Data on feeding habits and prey availability show that the major costs of small size are a reduction in food niche breadth and prey biomass resulting from restrictions on the type and size of prey eaten, and large territory requirements. Major benefits of small size are the ability to subsist on small, numerous and accessible arthropods with high encounter rates, enabling coexistence with larger congeners and exploitation of low-productivity habitats less suitable for larger earthworm-eating species. Small size, coupled with low per capita food intake, is shown to be of special adaptive value in cold winters when food supply is restricted mostly to small arthropods, and earthworms are few.     

Determinants of territory size in the pomacentrid reef fish,Parma victoriae

Summary Factors governing the size of territories defended by the pomacentrid reef fish, Parma victoriae, were investigated, prompted by contradictory predictions in the literature concerning the effects of food supply and competitors. Observations were carried out over the non-breeding period (March–October) on a medium density population in which territories were partially contiguous. The territory size of adult fish varied between 3 and 26 m², and was inversely correlated with local densities of conspecifics. The same range in territory size was found for both males and females, which did not differ in the time they spent on territory defence and foraging activities. No correlation existed between territory size and the abundance of algal food, body size, age or time spent on territory defence. Also, there was little variation in territory size over time, despite seasonal changes in the abundance of food algae.Experimental reduction of food supplies on isolated territories of males and females had no effect on territory size. In a higher density habitat an experiment was carried out in which population density and food abundance were simultaneously manipulated. This showed that territory size was primarily determined by intraspecific interactions, as territories exhibited considerable increases in size upon removal of neighbours. No changes in the size of defended areas resulted from either artificial increases or decreases of food levels. There were also no changes in the time spent on defence of territories, foraging time or feeding rates associated with food manipulations or territory expansion, which suggested that food was not a limited resource. This conflicted with current theories proposed to explain territory defence and expansion. It is hypothesized that intraspecific interactions constrain territory size well below the optimum in terms of the abundance of preferred food algal species.     

Experimental fruit removal does not affect territory structure of wintering Hermit Thrushes

ABSTRACT.   Food is generally considered to be the primary resource structuring winter territories in migrant songbirds, but there is little experimental evidence to support this. In southeastern Louisiana, ripe fruits, consumed opportunistically in the absence of preferred arthropod resources, are a primary food resource for wintering Hermit Thrushes ( Catharus guttatus ). To test the possible role of food in controlling space use during the winter, we reduced fruit availability in the territories of wintering Hermit Thrushes and compared responses of these thrushes to those in control territories where fruit availability was not altered. We found that thrushes did not adjust either territory size or location in response to midwinter reduction of fruit availability. One possible explanation for this lack of response is that sufficient food, including arthropods, was available in thrush territories even after removal of fruit. Another possibility is that the removal of fruit did reduce food levels below the level needed to meet energetic needs, but social constraints on territory structure, dictated by fall settlement spacing and maintained by agonistic interactions, prevented birds from adjusting territories to match food supply later in the season.     

Temporal pattern of foraging and microhabitat use by Galápagos marine iguanas,Amblyrhynchus cristatus

We observed a colony of marine iguanas (Amblyrhynchus cristatus) on Isla Fernandina, Galápagos, Ecuador, while measuring local micrometeorological and tidal conditions. We found size-related differences in foraging mode, with smaller iguanas feeding intertidally during daytime low tides and larger iguanas feeding subtidally. Despite having greater opportunity, subtidal foragers did not time their foraging bouts or exploit their environment in ways that optimized their period at high body temperature. Instead, the foraging schedule of these iguanas served to maximize their rate of rewarming following emergence from the cool sea. Intertidal feeders, by contrast, showed much greater behavioral flexibility in attempting to exploit their thermal environment. We suggest that size-ordered differences in marine iguana thermoregulatory behavior reflect underlying ontogenetic changes in costs and benefits of thermoregulation due to differences in predator pressure, quantity of food and electrolytes taken at each feeding, mode of foraging, and agonistic tendencies.     

Long-term hoarding in the Paridae: a dynamic model

Using stochastic dynamic programming we modeled the hoardingand foraging behavior of tits and chickadees, Pandas, that areresident in the boreal forest at high latitudes. Here autumnshave a rich supply of seeds and temperatures are relativelymild, while winters are cold with short days and a low foodsupply. We assumed that parids have a memory of limited durationand that forgotten seeds accumulate in a bank that adds to thegeneral food supply in the hoarder's territory. Our model predictsthat birds should start "high-intensity" hoarding in early autumn,but not before that. Because of mass-dependent costs the birdswill keep their fat levels low during the autumn. When winterarrives they will carry more body fat, both for the long winternights and to hedge against the large effects of weather variationsin winter. After increasing the fat level at the start of winter,fat should gradually increase even more, to compensate for thediminishing food supply. Most hoarding occurs in autumn as away of building up the supply of long-term stores. Remembered,or short-term caches, may hedge against stochastic events inthe environment. Even though conditions are not beneficial forhoarding in winter, the birds still stored in winter to maintainlarger short and long-term hoards if environmental variationincreased. Almost all time in winter that not was spent foragingwas spent perching, mainly to avoid predation     

Population density affects foraging behavior of male Black-throated Blue Warblers during the breeding season

ABSTRACT.   Foraging behavior often reflects food availability, a resource that may increasingly limit breeding birds as intraspecific crowding increases. Measuring foraging behavior, therefore, provides a way to investigate effects of population density on food limitation, an important link in understanding how crowding functions to regulate populations. We quantified three components of foraging behavior (prey attack rate, foraging speed, and relative use of morphologically constrained attack maneuvers) for male Black-throated Blue Warblers ( Dendroica caerulescens ) breeding under experimentally manipulated density conditions. Building on the previous work showing the density of conspecific neighbors affects territory size, reproductive success, and the time budgets of males ( Sillett et al. 2004 , Ecology 85: 2467–2477), we further show that density affects male foraging strategies. Although not differing in attack rate or foraging speed, male Black-throated Blue Warblers on territories with reduced neighbor densities used energetically expensive aerial attack maneuvers significantly less frequently than males in control (high-density) territories during both the incubation period and when provisioning nestlings and fledglings. We conclude that males altered their foraging behavior to compensate for density-related reductions in time available for foraging and that population density may constrain the time available for foraging.