鄱阳湖越冬鹤鹬的日间行为节律

目前有关鸟类越冬行为节律的研究主要集中在大型水鸟。与大型鸟类相比,小型鸟类在体温调节中消耗的能量更多,因此可能呈现不同的日间行为节律。本研究选择鄱阳湖数量较大的小型水鸟——鹤鹬Tringa erythropus为研究对象,于2014年11月—2015年3月在鄱阳湖的子湖——常湖池对越冬期鹤鹬各种行为的时间分配进行了调查研究。结果表明觅食(61.4%)和休息(32.1%)是鹤鹬越冬期最主要的行为,2种行为的比例呈显著负相关。与一些植食性水鸟相比,肉食性鹤鹬的觅食行为比例偏低。而与一些大型食肉性水鸟相比,鹤鹬的觅食行为比例偏高,这可能与其较小的体型在体温调节中消耗的能量较多有关。鹤鹬的警戒行为比例较低(0.8%),越冬期集大群的习性可能是导致其偏低的主要原因。越冬期不同月份间各行为比较中,1月出现了觅食行为比例的高峰和休息行为比例的低谷,这可能与1月平均气温为全年最低有关。觅食行为比例在全天呈缓慢上升趋势,而休息行为比例呈下降趋势。虽然觅食和休息行为的时间分配在全天有一定变化,但是鹤鹬的日间行为节律性并不强。鹤鹬的觅食行为主要发生在跗跖位(0~5.5 cm),而休息行为主要发生在跗跖上位(5.5~8.6 cm),安全性和食物的可利用性可能是影响鹤鹬生境选择的主要因素。     

昆明翠湖越冬红嘴鸥日间行为节律及行为时间分配

昆明翠湖是昆明越冬红嘴鸥Larus ridibundus的重要栖息地之一。为了解红嘴鸥越冬期的日间行为模式,掌握其活动规律,2017年11月—2018年2月和2018年11月—2019年2月,采用瞬时扫描法在翠湖水域对越冬红嘴鸥日间行为节律及行为时间分配进行了研究,采用Kruskal-Wallis H检验、单因素方差分析对不同时段内越冬红嘴鸥行为时间分配的差异进行了分析,并采用Pearson检验法检验了各行为间的相关性。结果表明,越冬期红嘴鸥行为时间分配比例为:觅食(44.01±1.70)%、休息(18.84±0.93)%、修整(9.44±1.00)%、警戒(2.45±0.57)%、行走(3.01±0.39)%、游泳(13.77±1.01)%和飞行(8.47±0.68)%。其中,行走和飞行行为在日间各时段内的差异有高度统计学意义(P0.01),具有明显的日节律性变化,其他行为之间的差异无统计学意义;觅食(F=9.112,P0.01)、休息(F=12.798,P0.01)行为在不同月份间的差异有高度统计学意义,而警戒行为在不同月份间的差异有统计学意义(F=3.358,P0.05),具有明显的月节律性变化。昆明翠湖越冬红嘴鸥在整个越冬期间以补充、积累能量为主;日间行为存在明显的"上午觅食+中午休息+下午觅食"的行为模式,一天中最主要的行为是觅食。     

崇明东滩人工湿地越冬水禽行为观察

2006年12月上旬-2007年2月下旬,在崇明东滩堤内次生人工湿地(鱼-蟹塘)对7种优势种水禽的昼间(6:30-17:30)行为进行了观察.结果表明:白鹭(Egrettagarzetta)、苍鹭(Ardea cinerea)和斑嘴鸭(Anas poecilorhyncha)以停伫行为为主,分别占全天行为的34.09%、45.45%和54.55%;白骨顶(Fulica atra)、普通鸬鹚(Phalacrocorax carbo)取食行为较活跃,分别占全天行为的32.58%和35.00%;小鹛鹧(Tachybaptus ruficollis)和银鸥(Larus argentatus)游水活动分别占全天行为的44.70%和31.82%.此外,环境温度和光照与水禽活动呈正相关,与风速负相关,湿地内水位由于变化不大而对越冬水禽行为影响不显著.     

郑州地区夜鹭越冬生态调查

20 0 0～ 2 0 0 3年在郑州森林公园对夜鹭 (Nycticoraxnycticorax)的越冬种群进行了调查。结果表明 ,每年 9月越冬夜鹭在此集群 ,1 2月达到高峰 ,数量为 ( 1 697± 49)～ ( 1 95 0± 73 )只。越冬种群以成体为主 ,亚成体不超过种群的 7 84%。夜鹭在越冬地滞留的时间超过 5个月 ,至翌年 3月初离开越冬地迁往 7km外的市区繁殖。越冬期间 ,夜鹭白天静卧树枝上休息 ,日落后 8～ 3 2min外出觅食 ,日出前约 1h返回林中。隆冬季节部分夜鹭推迟觅食或并非每天外出觅食。在郑州森林公园安全越冬的个体仅为越冬最大种群的 3 4 46% ,导致夜鹭数量减少和死亡的原因主要为低温引起的食物短缺 ,致使部分个体扩散到其它区域或饥饿致死。本区为已报道的夜鹭越冬最北界 ,夜鹭由此产生一系列生态适应 ,白天活动减少 ,下树避风取暖 ,觅食习性也有所改变。     

鄱阳湖四种水鸟的栖息地利用与水深和食物的关系

为了了解水深和食物资源对水鸟栖息地利用的影响,2012 ~ 2013年越冬期,采用样方法,对鄱阳湖沙湖的白鹤 (Grus leucogeranus)、小天鹅 (Cygnus columbianus)、东方白鹳 (Ciconia boyciana) 和白琵鹭 (Platalea leucorodia) 4种水鸟的数量、觅食地和休息地的水深以及主要食物——沉水植物冬芽的密度和生物量进行了调查。每个样方为150 m? 150 m的栅格,全湖共设置152个样方。结果显示,10月份沉水植物冬芽的平均水深为 (124.2 ± 12.0) cm。4种水鸟觅食地的水深均显著高于其休息地的水深 (白鹤：Z = 11.96, 小天鹅：Z = 4.69, 东方白鹳：Z = 14.44, 白琵鹭：Z = 29.33, 所有P < 0.01);对于2种食冬芽的水鸟,白鹤觅食地的水深、冬芽生物量、取食深度以及休息地水深均显著低于小天鹅 (觅食地水深: Z = 8.56, 冬芽生物量: Z = 2.93, 取食深度: Z = 14.69, 休息地水深: Z = 4.34, 所有P < 0.05),但两者觅食地的冬芽密度差异不显著 (Z = 0.6, P = 0.55);对于2种食鱼性水鸟,东方白鹳觅食地水深、取食深度和休息地水深均显著大于白琵鹭 (觅食地水深: Z = 10.60; 取食深度: Z = 9.35; 休息地水深: Z = 8.47, 所有P < 0.01)。回归分析表明,白鹤、东方白鹳、白琵鹭的觅食个体数量均与水深呈二次项关系,个体数量最大的觅食地水深分别为23.9 cm,33.0 cm和22.6 cm;白鹤、小天鹅的觅食个体数量均与冬芽生物量呈线性关系。3种涉禽均只能分布在一定的水深范围内,且同种食性的水鸟利用不同的水深从而减少在空间生态位的重叠。     

云南纳帕海黑颈鹤越冬行为与生境利用初步观察

2005年10月～2006年3月在纳帕海自然保护区对黑颈鹤越冬期行为和生境利用进行了30天观察.采用扫描取样和目标取样对黑颈鹤的行为和生境利用进行了观察.将行为划分为觅食、喂食与索食、伫立、休息、运动、保养、社群等7种.整个越冬期黑颈鹤的主要行为是觅食,觅食行为在越冬中、末期在所有行为所占比例逐渐增加.黑颈鹤的觅食行为60%以上发生在沼泽,其次是沼泽畔的草地.因此,保护好湿地沼泽对黑颈鹤在纳帕海顺利越冬极为重要.     

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。     

福建省兴化湾滨海养殖塘冬季水鸟的栖息地利用

20D7年12月至2008年3月对福建省兴化湾东北部江镜华侨农场(25°29′～25°33′N,119°23′～119°26′E)滨海养殖塘水鸟的栖息地利用进行了研究.选取了6个养殖塘作为样地,总面积360 hm2,共记录到水鸟6目8科25种.潮汐变化是影响养殖塘内越冬水鸟栖息的重要因素.高、中、低3种不同潮位下养殖塘水鸟群落特征差异较大.水鸟的种数和数量随潮水的涨高而显著增加,优势种则减少;多样性指数和均匀性指数随潮水的涨高而降低,优势度则增大.养殖塘的水深是影响水鸟栖息的另一个重要因素.4个不同水深区域水鸟群落的种类组成及密度差异显著,鸻鹬类、鸥类、鹭类等鸟类在中等水位区和浅水区栖息,鸭类主要栖息在深水区,而无水区仅有少数鹭类活动.在潮汛期间,滨海养殖塘是水鸟良好的临时栖息地,科学管理可使养殖塘人工湿地与潮间带滩涂共同满足越冬水鸟的栖息需求.     

福建兴化湾黑脸琵鹭觅食生境的鱼类和虾类组成

黑脸琵鹭(Platalea minor)的食物主要由鱼类和虾类组成,对其觅食生境中潜在食物的分析有助于对该濒危物种的保护。福建兴化湾是我国大陆黑脸琵鹭最重要的越冬地之一,对湾内越冬黑脸琵鹭的观察发现,黑脸琵鹭白天在养殖塘休息,黄昏则飞到离养殖塘约8km处的滩涂觅食至黎明返回。在黑脸琵鹭觅食的滩涂共采集到42种鱼类和6种虾类。根据对体长、生活习性和数量状况的分析,认为其中的19种鱼类和6种虾类为黑脸琵鹭的潜在食物,以鲻科鱼类最为重要。建议对黑脸琵鹭的保护应重视其觅食滩涂生境中鱼类和虾类资源的保护。     

云南拉市海灰鹤的越冬行为初步观察

2004年10月～2005年3月初步观察了云南拉市海保护区灰鹤(Grus grus)的越冬行为.灰鹤在拉市海的越冬期为175～180 d.10月初至11月下旬为灰鹤在拉市海的"迁入期",11月底至12月底为"过境停留期",1月初至3月中旬为"稳定越冬期",3月中下旬为"迁出期".越冬期日间活动以取食为主,占据了75.53%左右的时间,其次为警戒14.66%、护理5.05%、休息4.49%,4种行为的时间分配在各时间段之间差异极显著.在越冬个体中,家庭单位中的成鹤和幼鹤都是比集群中的个体利用更少的时间取食和更多时间警戒,说明较大的群体规模可以降低个体面临的捕食风险.     

长江口滩涂围垦后水鸟群落结构的变化——以南汇东滩为例

近年来长江口滩涂湿地高强度的促淤围垦对生物多样性保育造成了严重影响。本研究于2006至2010年在南汇东滩进行了水鸟调查,研究围垦后堤内环境的快速演替过程对水鸟的群落结构的影响。通过分析鸻鹬类、雁鸭类和鹭类三类主要水鸟类群,结果表明鸻鹬类的总数呈严重下降趋势（ANOVA, p=0.009）,而雁鸭类和鹭类总数在上升（ANOVA,p=0.015;p=0.00）;在种类数量方面,鸻鹬类和雁鸭类差异不显著（ANOVA,p=0.597;p=0.523）,鹭类种类数变化极显著（ANOVA ,p=0.00）。同时,通过对水鸟的栖息地选择因子偏好的分析, 发现滩涂减少是鸻鹬类减少的主要因素,而大型鱼塘和芦苇增加是雁鸭类和鹭类增加的重要原因。为此我们提出相应海岸带湿地管理建议。     

Diel Cycles in Chemosensory Behaviors of Free‐Ranging Rattlesnakes Lying in Wait for Prey

The sensory ecology of foragers is fundamentally influenced by changes in environmental conditions such as ambient light. Changes in ambient light may hinder the effectiveness of particular senses (e.g., impaired vision at night), but many predators rely on multiple sensory systems and may continue to forage despite changes in light availability. Exactly how predator behaviors and sensory systems compensate under changes in light availability in the field is not well understood. We used radio telemetry and portable video surveillance cameras to quantify the sit‐and‐wait chemosensory foraging behavior of free‐ranging red diamond (Crotalus ruber) and northern Pacific (Crotalus oreganus oreganus) rattlesnakes during day and night periods. The two most common behaviors we observed were chemosensory probes, a behavior we describe in detail for the first time, and mouth gapes. During chemosensory probes, rattlesnakes extend their head beyond their coil, explore the surrounding area while tongue‐flicking, and subsequently return to a stationary position inside their coil. Foraging rattlesnakes probed at significantly higher rates during nocturnal vs. diurnal hours. Similarly, mouth gaping occurred during a higher percentage of nocturnal vs. diurnal hours for foraging snakes. Nearly half of all mouth gapes were followed immediately with a chemosensory probe, suggesting that mouth gaping also serves a chemosensory function in this context. Our results suggest that chemical cues play an increasingly important role in mediating rattlesnake foraging behavior at night. Examining how abiotic factors, such as light availability, influence the sensory ecology of free‐ranging predators is essential for accurately characterizing their interactions with prey.     

Flight by night or day? Optimal daily timing of bird migration

Many migratory bird species fly mainly during the night (nocturnal migrants), others during daytime (diurnal migrants) and still others during both night and day. Need to forage during the day, atmospheric structure, predator avoidance and orientation conditions have been proposed as explanations for the widespread occurrence of nocturnal migration. However, the general principles that determine the basic nocturnal-diurnal variation in flight habits are poorly known. In the present study optimal timing of migratory flights, giving the minimum total duration of the migratory journey, is evaluated in a schematic way in relation to ecological conditions for energy gain in foraging and for energy costs in flight. There exists a strong and fundamental advantage of flying by night because foraging time is maximized and energy deposition can take place on days immediately after and prior to the nocturnal flights. The increase in migration speed by nocturnal compared with diurnal migration will be largest for birds with low flight costs and high energy deposition rates. Diurnal migration will be optimal if it is associated with efficient energy gain immediately after a migratory flight because suitable stopover/foraging places have been located during the flight or if energy losses during flight are substantially reduced by thermal soaring and/or by fly-and-forage migration. A strategy of combined diurnal and nocturnal migration may be optimal when birds migrate across regions with relatively poor conditions for energy deposition (not only severe but also soft barriers). Predictions about variable timing of migratory flights depending on changing foraging and environmental conditions along the migration route may be tested for individual birds by analysing satellite tracking results with respect to daily travel routines in different regions. Documenting and understanding the adaptive variability in daily travel schedules among migrating animals constitute a fascinating challenge for future research.     

Contribution of diurnal and nocturnal insects to the pollination of Jatropha curcas (Euphorbiaceae) in southwestern China

Jatropha curcas L. (Euphorbiaceae) is being increasingly planted worldwide, but questions remain regarding its pollination biology. This study examined the contribution of diurnal and nocturnal insects to the pollination of monoecious J. curcas, through its floral biology, pollination ecology, and foraging behavior of potential pollinators. Nectar production of both male and female flowers peaked in the morning, declined in the afternoon, and rapidly bottomed during the night in all of their anthesis days. The diurnal visitors to the flowers of J. curcas are bees and flies, and the nocturnal visitors are moths. Flowers received significantly more visits by diurnal insects than by nocturnal insects. Through bagging flowers during night or day or both or exclusion, we compared fruit and seed production caused by diurnal and nocturnal pollinators. Both nocturnal and diurnal visitors were successful pollinators. However, flowers exposed only to nocturnal visitors produced less fruits than those exposed only to diurnal visitors. Thus, diurnal pollinators contribute more to seed production by J. curcas at the study site.     

Diel activity of resident and immigrant waterbirds at Lake Turkana, Kenya

Of the 42 dominant species of waterbirds at Lake Turkana, Kenya, 14 foraged uniformly throughout the day and night, five foraged mostly during the night, five foraged during both the night and day but with diurnal peaks, 17 were exclusively diurnal and only one was exclusively nocturnal. Species with uniform feeding activity usually captured small prey, using tactile or visual plus tactile cues; most diurnal species captured large prey, using visual cues. However, some species which fed mostly at night, or uniformly, relied exclusively on visual cues. We found support from only one species that moonlight influenced foraging activities. Palaearctic immigrants spent significantly more time foraging than partial migrants and residents; they were also smaller and mainly microphagous. Only gulls and terns were restricted to diurnal feeding, presumably by their need to see and capture prey while flying. The other groups were formed by species which foraged uniformly over 24 h or partially by day or night. These patterns indicate that in most waterbirds feeding activities are not basically tied to any phase of the diel cycle. Since most waterbirds display some degree of nocturnal activity, time budget studies based only on diurnal observations are likely to be misleading.     

Extrafloral‐nectaries and interspecific aggressiveness regulate day/night turnover of ant species foraging for nectar on Bionia coriacea

Plants bearing extrafloral nectaries (EFNs) vary the secretion of nectar between day and night, which creates turnover in the composition of interacting ant species. Daily variation in the composition of ant species foraging on vegetation is commonly observed, but its mechanisms are poorly understood. We evaluated the daily variation in nectar availability and interspecific aggressiveness between ants as possible regulatory mechanisms of the turnover in ant–plant interactions. We hypothesized that (i) plants would interact with more ant species during periods of higher secretion of nectar and that (ii) aggressive ant species would compete for nectar, creating a daily turnover of species collecting nectar. We tested this hypothesis by measuring the production of nectar during the day and night and by experimentally removing EFNs of Bionia coriacea (=Camptosema coriaceum) (Nees & Mart.) Benth. (Fabaceae: Faboideae) plants in a Brazilian savanna (Cerrado). We then compared the abundance and composition of ant species between those treatments and during the day. Our results indicate that more ant workers forage on plants during the day, when nectar was sugary, while more ant species forage at night, when aggressiveness between ant species was lower. We also detected a day/night turnover in ant species composition. Ant species foraging for nectar during the day were not the same at night, and this turnover did not occur on plants without EFNs. Both dominant ant species, diurnal Camponotus crassus (Hymenoptera: Formicidae) and nocturnal Camponotus rufipes (Hymenoptera: Formicidae), were the most aggressive species, attacking other ants in their specific periods of forage while also being very aggressive toward each other. However, this aggressiveness did not occur in the absence of nectar, which allowed non‐aggressive nocturnal ant species to forage only during the daytime, disrupting the turnover. We conclude that extrafloral‐nectar presence and interspecific aggressiveness between ants, along with other environmental factors, are important mechanisms creating turnovers in ants foraging on plants.     

THE OCCURRENCE AND ADAPTIVE SIGNIFICANCE OF NOCTURNAL HABITS IN WATERFOWL

This paper reviews the occurrence of nocturnal activity, particularly foraging, in wildfowl (Anseriformes) and shorebirds (Charadrii), and discusses its significance. Many duck species are mainly active at night while others regularly feed during both the day and night. Some ducks and geese are normally day feeders and occasionally forage during darkness. In a few duck species, courtship also has been observed at night. Most shorebirds forage both by day and night, in temperate and in tropical latitudes. Some are mainly crepuscular and nocturnal feeders and also display at dusk and at night. Some species may use their daytime territory at night. A few shorebird species, including some visual peckers and long-billed tactile probers, use the same foraging method to detect and capture food by night as by day. However, some long-billed species that forage visually during daytime modify their feeding techniques and rely completely or partly on tactile means for detecting prey at night. Large eyes seem an advantage to plovers and other sight feeders for night feeding. Numerous touch-sensitive corpuscles in the bill of ducks and many scolopacid species favour tactile feeding. Some ducks, geese and shorebirds may especially use moonlit nights for feeding though, in a few species, moonlight seems to have no effect. The possible role of bioluminescence is also discussed. Nocturnal activity may occur for two reasons. The night may be preferred because foraging is more profitable or safest from predators. Alternatively, birds may be forced to forage at night because they fail to collect all their food requirements during the day. The evidence for both hypotheses is reviewed. Nocturnal activity does appear to allow wildfowl, and perhaps shorebirds, to avoid diurnal predators (including man). Shorebirds, and some ducks also seem to take advantage of prey that are more abundant and/or accessible at night. The main evidence for the supplementary feeding hypothesis comes from studies of seasonal variations in the occurrence of nocturnal feeding, about which rather little is known at present. The increasing availability of modern night-viewing equipment may help to fill this gap. There are two important implications arising from the widespread occurrence of nocturnal activity in wildfowl. Most knowledge on time and energy budgets is based on daytime studies, and so may need to be revised. Wintering dabbling ducks and shorebirds, at least in some regions, may use different habitats by day and by night. If confirmed, there would be a need to preserve some wintering habitats which, although little used by ducks and shorebirds during the day, may be intensively used at night.     

Foraging strategies of Eriophora transmarina and Nephila plumipes (Araneae: Araneoidea): Nocturnal and diurnal orb-weaving spiders

Abstract The foraging behaviour, web characteristics and prey availability of two sympatric orb-weaving spiders, Nephila plumipes and Eriophora transmarina (Araneae: Araneoidea), are compared. The spiders are similarly sized but have different temporal foraging patterns. Nephila plumipes spins a relatively permanent web and captures most of its prey during the day. Eriophora transmarina only forages at night, spinning a new web every night and usually dismantling it at dawn. These different foraging activities are most likely to be responsible for the observed differences in the types and rates of prey capture: E. transmarina captured mostly Lepidoptera that were more abundant at night than during the day, while N. plumipes captured mostly Hymenoptera that were more abundant during the day than at night. While nocturnal E. transmarina have less time available for foraging than the diurnal N. plumipes, the former has a substantially higher nocturnal prey capture rate. We argue that the difference between the species in their prey capture rates are likely to be due to differences in the architecture of their webs.     

Patterns of GPS tracks suggest nocturnal foraging by incubating Peruvian pelicans (Pelecanus thagus)

Most seabirds are diurnal foragers, but some species may also feed at night. In Peruvian pelicans (Pelecanus thagus), the evidence for nocturnal foraging is sparse and anecdotal. We used GPS-dataloggers on five incubating Peruvian pelicans from Isla Lobos de Tierra, Perú, to examine their nocturnality, foraging movements and activities patterns at sea. All instrumented pelicans undertook nocturnal trips during a 5–7 day tracking period. Eighty-seven percent of these trips (n = 13) were strictly nocturnal, whereas the remaining occurred during the day and night. Most birds departed from the island after sunset and returned a few hours after sunrise. Birds traveled south of the island for single-day trips at a maximum range of 82.8 km. Overall, 22% of the tracking period was spent at sea, whereas the remaining time was spent on the island. In the intermediate section of the trip (between inbound and outbound commutes), birds spent 77% of the trip time in floating bouts interspersed by short flying bouts, the former being on average three times longer than the latter. Taken together, the high sinuosity of the bird''s tracks during floating bouts, the exclusively nocturnal trips of most individuals, and the fact that all birds returned to the island within a few hours after sunrise suggest that pelicans were actively feeding at night. The nocturnal foraging strategy of Peruvian pelicans may reduce food competition with the sympatric and strictly diurnal Guanay cormorants (Phalacrocorax bougainvillii), Peruvian boobies (Sula variegata) and Blue-footed boobies (S. nebouxii), which were present on the island in large numbers. Likewise, plankton bioluminescence might be used by pelicans as indirect cues to locate anchovies during their upward migration at night. The foraging success of pelicans at night may be enhanced by seizing prey close to the sea surface using a sit-and-wait strategy.     

Tropical pollinators in the canopy and understory: Field data and theory for stratum “preferences”

Claims have been made for a canopy preference by large bees pollinating tropical flowers—without data or tests that support or refute this opinion. The working hypothesis for bee foraging behavior in three dimensions is that forager experience can produce stratum fidelity, just as rewarding foraging produces floral fidelity. Wideranging search behavior should allow bees to track spatiotemporal distribution of resources. A systematic study of 20 bee species and 10 genera: Apis, Trigona, Eulaema, Centris, Euglossa, Scaptotrigona, Partamona, Megalopta, Rhinetula,and Oxytrigonawas made in two forests in Panama. Two traps were operated simultaneously at canopy height and in the understory to test whether there were consistent stratum associations. Studies were continuous for 1 and 8 years. The only high-canopy foragers were two nocturnal bees, all the rest flew at both heights with similar probability or consistently came to lower traps. Large euglossines showed a tendency to forage high, which was directly related to their capacity for heat loss during flight, compared to smaller euglossines. They are also more conspicuous in warning coloration, another expected correlate of foraging more often in the open. Although large variance in stratum association predominates, some medium-sized diurnal forest bees avoid the exposed upper canopy, while some nocturnal bees tend to forage there.