Seasonal variations in feeding range and flock structure of the Rook Corvus frugilegus in eastern Ireland

The feeding range and flock structure of Rooks showed temporal variations caused mainly by the dispersion of food and reproductive behaviour.
Feeding range was restricted in spring, autumn and early winter when food availability was high and Rooks were reproductively active. A large feeding range occurred in late summer and late winter, when food availability was either generally low or locally distributed and when Rooks were reproductively inactive. The occurrence of flocks common to several rookeries mirrored variations in feeding range; mixed rookery flocks were more common in late summer and late winter. Similarly, the size of the rookery (as measured by the number of nests) was related to feeding range only when Rooks were reproductively inactive and at such times larger rookeries had greater feeding ranges.
Flock structure showed similar seasonal variations; small widely spaced flocks predominated in summer, autumn, early winter and spring, whereas large dense flocks occurred in late winter. Diurnal variations in flock structure occurred within any one season. Both seasonal and diurnal variations in flock structure may be determined by the dispersion of the prey and the feeding strategy used to obtain it, reproductive behaviour and the risk of predation.     

Diet and feeding habits of Economidichthys pygmaeus (Perciformes: Gobiidae) in Lake Pamvotis,NW Greece

The purpose of the study was to define the diet composition, feeding preferences, seasonal, size and sex related changes in diet, feeding strategy and diel cycle of Economidichthys pygmaeus. Important features of the overall feeding patterns of the goby include (i) feeding activity, (ii) bottom habits and (iii) consumption of food items to identify the dietary breadth. Stomach contents of 533 specimens, 13.42–48.65 mm total length (TL), collected by hand net (2 mm mesh size) from October 2006 to September 2007 were analyzed. The percentage of 76 empty stomachs (14.26%) did not vary significantly with season. The food composition suggested that the goby is a carnivorous fish. Prey items identified in the stomachs belonged to four major groups: Crustaceans, Insects, Mollusca and Plants. Copepods were the most important (%IRI = 57.51), especially in fish larger than 23 mm TL. Chironomids (%IRI = 43.23) constituted the main prey for fish <23 mm TL. Diet composition showed little seasonal variation. Copepoda dominated the diet in autumn and winter (43.4%; 82.4%) and were replaced by Chironomidae larvae in spring (39.7%) and summer (47.7%). During the reproductive season, large males show a narrow food spectrum as opposed to large females, reflecting the different activity pattern exhibited by males and females during the breeding season, since the former supports parental care. According to the modified Costello graphical method, specialist individuals form the goby population that feeds on two preferential prey types (e.g. Copepods, Chironomids). Nevertheless, they consume some occasional prey (e.g. Cladocera, Insects, Gastropods). The species foraged chiefly at night and early morning, during lower light intensity. The highest feeding activity recorded at night (02.00 hours) and during early morning (08.00 hours) could be related to the cryptic behaviour displayed by the species.     

Diel feeding rhythms and daily food consumption of juvenile Atlantic salmon in the River Alta, northern Norway

Atlantic salmon fry (0+) sampled from the River Alta exhibited only minor differences in stomach content weights and feeding rates throughout diel periods, but feeding rates were generally lowest at night. In contrast, salmon parr (1+ to 3+) had large diel fluctuations in stomach content weight, with the largest weights usually being recorded during the night and early morning. Accordingly, their feeding rates were highest at night. This nocturnal feeding pattern was consistent throughout all sampling occasions, and appeared to reflect a persistent feeding periodicity in the salmon parr. The daily food consumption rates of both fry and parr were highest during midsummer and decreased towards autumn.     

永定河流域大型底栖动物功能摄食类群时空分布及生态评价

2017年春季(4月)、夏季(7月)、秋季(11月)对永定河流域23个样点的大型底栖动物、水环境和水文因子进行了野外调查,分析了永定河流域大型底栖动物功能摄食类群的群落组成与时空分布特征及其对河流生境变化的响应情况。永定河流域3个季节共采集到大型底栖动物78种,隶属3门6纲39科,其中,春季52种、夏季50种、秋季53种,功能摄食类群以收集者占绝对优势,其次为捕食者,刮食者、滤食者、撕食者所占比例极低。3个季节优势种均属于收集者类群,春季优势种为直突摇蚊属、流水长跗摇蚊属、环足摇蚊属,夏季优势种为雕翅摇蚊属,秋季优势种为多足摇蚊属、摇蚊属、直突摇蚊属。冗余分析结果表明: 水温、流速、盐度以及总磷是影响春季大型底栖动物功能摄食类群的主要影响因子;总磷、溶解氧、电导率以及流量是夏季大型底栖动物功能摄食类群的主要影响因子;总磷和溶解氧是影响秋季大型底栖动物功能摄食类群的主要影响因子;总磷在春、夏、秋季均与收集者类群表现出正相关性,表明永定河流域大型底栖动物功能摄食类群受到了水质污染的影响。基于功能摄食类群参数的评价表明:1)物质循环方面,妫水河初级生产力显著高于其他区域,秋季大于其他季节;洋河次级生产力和分解能力显著高于其他区域,春季大于其他季节,但洋河自养/异养作用显著低于其他区域,春季小于其他季节;2)纵向输入能力方面,桑干河显著高于其他区域,秋季大于其他季节;3)沿岸物质的输入方面,妫水河显著高于其他区域,夏季大于其他季节。     

Brain aromatase, 5 alpha-reductase,and 5 beta-reductase change seasonally in wild male song sparrows: relationship to aggressive and sexual behavior

In many species, territoriality is expressed only during the breeding season, when plasma testosterone (T) is elevated. In contrast, in song sparrows (Melospiza melodia morphna), males are highly territorial during the breeding (spring) and nonbreeding (autumn) seasons, but not during molt (late summer). In autumn, plasma sex steroids are basal, and castration has no effect on aggression. However, inhibition of aromatase reduces nonbreeding aggression, suggesting that neural steroid metabolism may regulate aggressive behavior. In wild male song sparrows, we examined the neural distribution of aromatase mRNA and seasonal changes in the activities of aromatase, 5 alpha-, and 5 beta-reductase, enzymes that convert T to 17 beta-estradiol, 5 alpha-dihydrotestosterone (5 alpha-DHT, a potent androgen), or 5 beta-DHT (an inactive metabolite), respectively. Enzyme activities were measured in the diencephalon, ventromedial telencephalon (vmTEL, which includes avian amygdala), caudomedial neostriatum (NCM), and the hippocampus of birds captured during spring, molt, or autumn. Aromatase and 5 beta-reductase changed seasonally in a region-specific manner. Aromatase in the diencephalon was higher in spring than in molt and autumn, similar to seasonal changes in male sexual behavior. Aromatase activity in the vmTEL was high in both spring and autumn but significantly reduced at molt, similar to seasonal changes in aggression. 5 beta-Reductase was not elevated during molt, suggesting that low aggression during molt is not a result of increased inactivation of androgens. These data highlight the relevance of neural steroid metabolism to the expression of natural behaviors by free-living animals.     

Female dominance and feeding priority in a prosimian primate: experimental manipulation of feeding competition

Female dominance and feeding priority are considered unique behavioral strategies in many Malagasy lemuriformes, particularly Lemur catta. Two hypotheses have been introduced to explain these behavior patterns: 1) females are agonistically dominant over males to mitigate female-male food competition so that females can compensate for high energy demands and inefficient reproductive physiology, and 2) males defer to females when feeding as a reproductive strategy. We tested these hypotheses by conducting controlled feeding experiments on free-ranging ring-tailed lemurs (Lemur catta) on St. Catherine's Island, GA. Food was dispersed in three ways to simulate varying patch sizes. All feeding and agonistic interactions were recorded during each trial (n = 24). The degree of relatedness between individuals was determined using DNA fingerprinting. There was a clear relationship between food dispersion and both expression of female dominance and feeding priority. Elements of both hypotheses were supported because male and female L. catta used different strategies depending on rank and the dispersion of food. Interpretation of the impact of male rank was complicated because the younger, low-ranking males had female relatives in the group. Females fed more than males, and rates of aggression decreased as food dispersion increased. High-ranking, older unrelated males deferred to females and received little aggression. The top-ranking male deferred the most and sired most if not all of the offspring. Low-ranking, younger related males fought with females for access to food sources, received more aggression, and did not sire offspring.     

Reproductive seasonality of the nyala Tragelaphus angasi; The interaction of light, vegetation phenology, feeding style and reproductive physiology

In Ndumu Game Reserve, South Africa, it was found that nyala males exhibited no seasonal sexual cycle. Although conceptions occurred throughout the year, there was a bimodal pattern of conceptions with the peaks in autumn and spring.
After referring to other African bovids which also have bimodal patterns of reproductive activity, it was concluded that the cues for the two peaks are as yet unknown but must be provided by light or photoperiod. The factors which ultimately decide the amplitude of the peaks are vegetation phenology and feeding style of the animal. In nyala, peaks are masked by the occurrence of post-partum oestrous cycles and a gestation period of approximately 7 months.     

Choice of feeding sites by moose during summer, the influence of forest structure and plant phenology

We observed forage and habitat selection in radio-collared moose at feeding sites in southeast Norway. Use of older forest increased from spring to autumn. Birch Betula spp. and bilberry Vaccinium myrtillus accounted for c. 75% of the diet. Occurrence of important forage plants, height of browse, and difference in phenology between plant species all appeared to play a role in moose selection of feeding sites. Shading influences moose forage by delaying plant phenology and possibly through its effect on leaf content of water and secondary compounds. On single birch trees, feeding was concentrated to the top branches at midsummer; during spring and autumn more leaves from side branches were eaten. Greater discrimination as vegetation matured was also evident from the wider variety of forage species used at midsummer. Selection of feeding sites was not related to density of important browse species. We propose that variations in light/shade conditions may play a role in moose choice of feeding sites and that moose on summer range will benefit from a heterogeneous mixture of plantations and older forest stands.     

Migratory restlessness in the Yellow-faced Honeyeater Lichenostomus chrysops(Meliphagidae), an Australian diurnal migrant

The Yellow-faced Honeyeater Lichenostomus chrysops is a diurnal migrant which covers short to moderate distances in eastern Australia. Recordings of locomotor activity of nine wild-caught Yellow-faced Honeyeaters kept under a simulated natural photoperiod in the laboratory over a period of 13 months showed that these birds exhibit a distinct seasonal pattern in hopping activity. Two major seasonal peaks of enhanced activity were observed. The first occurred during the time of autumn migration in March to July, while a second peak from September to December coincided roughly with spring migration. Daily activity patterns of Yellow-faced Honeyeaters showed two major peaks. The first peak ranged from the early morning hours to approximately early afternoon, while a second smaller peak was observed in the late afternoon. During their migratory periods in spring and autumn, the morning as well as the afternoon peaks were considerably higher than in months when Yellow-faced Honeyeaters do not migrate.     

Daily feeding rhythms in Atlantic salmon II: size-related variation in feeding patterns of post-smolts under constant environmental conditions

Previous studies of feeding rhythms in post-smolt Atlantic salmon Salmo salar have produced variable results. Therefore, the present study was performed to clarify the source of these differences and to examine size-related variation in daily feeding patterns. A small group of hatchery reared post-smolts was kept in an indoor seawater tank under conditions of constant photoperiod and light intensity, and negligible diurnal variation in water temperature. Feeding responses were monitored by video camera throughout the day. The resultant feeding pattern for the population mirrored an earlier study, with the highest levels of feeding activity in the early morning and late evening. Differences between this and other studies may be due to variation in climate, season or life-history stage. Daily feeding patterns were size-dependent. The largest fish fed at a relatively constant level through the day, medium-sized fish fed in a pattern similar to that described above for the population and small fish fed most at first and last light. These differences were due probably to the effect of competitive interactions upon fish of different sizes.     

Brain aromatase, 5α‐reductase,and 5β‐reductase change seasonally in wild male song sparrows: Relationship to aggressive and sexual behavior

In many species, territoriality is expressed only during the breeding season, when plasma testosterone (T) is elevated. In contrast, in song sparrows (Melospiza melodia morphna), males are highly territorial during the breeding (spring) and nonbreeding (autumn) seasons, but not during molt (late summer). In autumn, plasma sex steroids are basal, and castration has no effect on aggression. However, inhibition of aromatase reduces nonbreeding aggression, suggesting that neural steroid metabolism may regulate aggressive behavior. In wild male song sparrows, we examined the neural distribution of aromatase mRNA and seasonal changes in the activities of aromatase, 5α‐, and 5β‐reductase, enzymes that convert T to 17β‐estradiol, 5α‐dihydrotestosterone (5α‐DHT, a potent androgen), or 5β‐DHT (an inactive metabolite), respectively. Enzyme activities were measured in the diencephalon, ventromedial telencephalon (vmTEL, which includes avian amygdala), caudomedial neostriatum (NCM), and the hippocampus of birds captured during spring, molt, or autumn. Aromatase and 5β‐reductase changed seasonally in a region‐specific manner. Aromatase in the diencephalon was higher in spring than in molt and autumn, similar to seasonal changes in male sexual behavior. Aromatase activity in the vmTEL was high in both spring and autumn but significantly reduced at molt, similar to seasonal changes in aggression. 5β‐Reductase was not elevated during molt, suggesting that low aggression during molt is not a result of increased inactivation of androgens. These data highlight the relevance of neural steroid metabolism to the expression of natural behaviors by free‐living animals. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 209–221, 2003     

Seasonality of recruitment and reproduction of Acanthocephalus tumescens (Acanthocephala) in fishes from Lake Moreno (Patagonia, Argentina)

The seasonality of recruitment and reproduction of Acanthocephalus tumescens at the component population level was investigated in Lake Moreno (Patagonia, Argentina). Seasonal samples of the principal fish host species were taken between spring 1999 and spring 2000. Prevalence, mean intensity, coefficient of dispersion, sex ratio, proportion of maturity stages of females, and percentages of the 2 sources of infection in the stomach of fishes were calculated. Overall prevalence, mean intensity, and coefficient of dispersion showed the same pattern of seasonal changes. The seasonal feeding patterns of fishes affect the occurrence of A. tumescens, producing 1 peak in spring and the other peak in autumn. The lower temperature in winter delay reproductive processes after the autumn period of recruitment.     

The feeding of trout during the filling phase of Rutland Water

Fingerling Salmo trutta L. and S. gairdneri R. were stocked in Rutland Water in early 1975. Initial rapid growth was associated with feeding on littoral and planktonic Crustacea during this year. Rapid water level changes occurred over the winter months, interspersed with longer periods of stability during the summer. These changes caused changes in trout diet. Terrestrial food (e.g. earthworms), released from flooded land was important during winter months; aquatic items which increased in abundance during periods of stable water levels (e.g. Gammarus pulex, Limnaea pereger, Chironomidae larvae and pupae) were important during spring, summer and autumn.It is suggested that the rapid growth rates recorded in the first two years of the reservoir are the result of the ready availability of different food sources.Present address: Department of Adult Education, University of Leicester, Leicester, EnglandPresent address: Department of Adult Education, University of Leicester, Leicester, England     

Resource partitioning of roach Rutilus rutilus and bleak Alburnus alburnus in two eutrophic lakes in SE Norway

In this paper I investigate the resource partitioning of roach Rutilus rutilus and bleak Alburnus alburnus in two eutrophic lakes in SE Norway. Zooplankton was the preferred food item for both species during summer, whereas blue-green algae dominated the diet in September/October. There was no diet overlap in May, with the roach feeding mainly on detritus and the bleak feeding on surface insects. During summer the diet overlap increased, reaching high values in autumn. Habitat overlap was close to unity in spring and early summer. Coinciding with increasing diet overlap during summer and autumn the overlap in habitat decreased.     

The feeding and energetics of stream-resident trout in winter*

The feeding of brook and brown trout in a temperate Canadian stream was studied over two winters. Stomach analyses indicate that feeding continues throughout the winter. Both species had similar diets. Despite continuous feeding, condition factors declined significantly in early winter and remained low until the spring, suggesting an early-winter depletion of lipid reserves. Energy (calorific) intake was similar in winter to that found in late summer or spring and therefore was not the cause of low winter condition. The derived energy from feeding was insufficient to offset the costs of maintenance metabolism in the early winter period, for both immature and recently spawned fish. It is suggested that stream-dwelling trout suffer a metabolic deficit during acclimation to rapidly declining water temperatures in November/December. Such a phenomenon has important physiological implications for overwinter survival.     

Hormonal Control of Seasonal Growth in a Temperate Zone Toad Bufo bufo

Young toads were exposed to a light regimen of 12L/12D at 21°C and fed meal-worms before hibernation in the autumn, when the toads reduce feeding and discontinue growth, and after hibernation in the spring, when feeding and growth is resumed. In the autumn treatment of the toads with bovine growth hormone maintained feeding and growth; in the spring the treatment protracted the period of feeding and growth. Thyroxin had no obvious effects on growth. It is concluded that the annual growth pattern of temperate zone toads is controlled by an internal rhythm in the secretion of growth hormone.     

Testosterone and autumn territorial behavior in male red grouse Lagopus lagopus scoticus

In many bird species, males exhibit territorial aggression outside the breeding season, when testosterone concentrations are low and may not regulate territorial behaviors. The hormonal regulation of aggression at this time of year has only been studied in passerine birds. Here, we investigated the role of testosterone in the regulation of aggression in a non-passerine bird, the red grouse Lagopus lagopus scoticus. Male red grouse are aggressive in early spring when breeding starts, in autumn when they establish territories, and sporadically through much of the winter. We first describe seasonal variations in plasma testosterone concentrations and in the size of males' sexual ornaments, their red combs, which relates to aggressiveness. Testosterone concentrations and comb size were correlated. Both increased in autumn to a peak in October, and then increased again in spring, to a greater peak in early April. Secondly, we experimentally investigated the effects of testosterone, and of an anti-androgen (flutamide) used in combination with an aromatase inhibitor (ATD), on autumn territorial behavior. Males were treated with either empty implants, as controls (C-males), testosterone implants (T-males), or with flutamide and ATD implants (FA-males). One month after implanting, both T- and FA-males had higher concentrations of testosterone than C-males. Comb size, aggressive call rate, and response to playbacks of territorial call all significantly increased in T-males. However, the increase in testosterone in FA-males did not increase comb size or aggressive behavior. In the following spring, after the content of implants was used, FA-males had significantly lower testosterone than C-males, and had a reduced seasonal increase in comb size. The results suggest that testosterone plays a significant role in regulating red grouse aggressive behavior in autumn. However, the observation that flutamide and ATD treatment did not reduce territorial behavior, suggests that estradiol may also be involved in the regulation of non-breeding aggression.     

鄱阳湖越冬雁类食源植被适宜取食时间窗口

雁类是长江中下游越冬水鸟的优势种群,以苔草(Carex spp)等湿生植被为主要食物来源。作为长江中下游仅存的通江湖泊之一,鄱阳湖显著受到水文波动的影响,湿地植被的生长发育与洲滩淹没和出露时间密切相关。雁类对食物资源具有高度的选择性,建立雁类取食植被的特征和苔草生长过程之间的关系,是刻画适宜栖息地时空分布范围,开展雁类及其食物资源保育的关键。选择鄱阳湖典型子湖泊常湖池作为研究区,对苔草春季生长期开展了原位观测试验,对4个高程梯度的苔草株高和生物量等关键生长因子进行了12次野外监测和采样。同时,结合遥感影像、气温数据及实地观测记录,确定了4个高程梯度洲滩的出露时间和苔草有效生长时间。在此基础上,建立了基于Logistic方程的苔草株高和生物量的生长过程曲线。并根据实地观测的雁类觅食苔草的特征,反推得到雁类适宜取食苔草的时间窗口。结果表明:苔草株高与地上生物量显著正相关,水文条件和气温是影响苔草生长的关键因素,而退水时间的推迟,会导致生长期缩短和低温限制下的有效生长时间减少,影响雁类食物资源的分布。苔草在秋季生长期出露达到12—28 d,而在春季生长期出露达到83—182 d时适宜雁类取食。研究提出了确定越冬雁类苔草适宜取食时间窗口的方法,证实洲滩退水时间推迟超过20 d,苔草生长节律将难以匹配雁类数量峰值期觅食的需要。本研究对鄱阳湖湿地水文调控和湿地资源管理具有重要意义。     

Development stage distribution as a proxy for feeding success and growth for first feeding Norwegian spring spawning herring larvae

The estimation of growth rates in young herring larvae (Clupea harengus) in the field can be difficult because the primary increments in the otoliths may not be discernible or formed at a daily level. Likewise, the estimation of mortality rates of fish larvae in the field is very difficult to achieve, especially in a rigorous quantitative manner. In this study, the authors suggest the use of a stage-based proxy of feeding success, growth and potential survival or mortality risk of field-caught larvae. The stage-based proxy is derived based on observations from previous laboratory studies where larvae successfully completing start-feeding on external food sources will advance through the early development stages, whereas those that do not (unsuccessful larvae) remain and accumulate in the development stage preceding first feeding. The relative occurrence of larvae in the early development stages is therefore expected to reflect feeding conditions of the larvae, with higher ratios of unsuccessful larvae indicative of poor feeding success and higher mortality risk. Using field data on Norwegian spring spawning herring, the authors document that the relative occurrence of larvae in the late non-feeding stage is significantly higher at lower average zooplankton concentrations, in line with the predictions of the authors that this novel approach of using a stage-based proxy could be a useful indication of feeding success, growth and mortality in the field. Further, there was a significant interaction effect with ambient temperature, with the ratio being higher at low zooplankton concentrations at higher temperatures. This study also suggests that these findings are not population specific as the same accumulation of non-feeding larvae in the late non-feeding stage was observed in laboratory-reared larvae of both autumn and spring spawning herring populations.     

Using aerial photography to investigate evidence of feeding by bowhead whales

Aerial photographs were analyzed to investigate the feeding habits of the Bering‐Chukchi‐Beaufort (BCB) population of bowhead whales (Balaena mysticetus), particularly epibenthic feeding near Barrow, Alaska. Evidence of epibenthic feeding was based on mud visible on the dorsal surface of whales, resulting from feeding near the seafloor. Other cues used to assess feeding were an open mouth or the presence of feces in photographs. Over 3,600 photographs were analyzed including photos from surveys in spring and late summer and in both the western and eastern Beaufort Sea. Of all the photographs analyzed, 64% were scored as definitively muddy. In spring, ratios ranged from a low of 27% in 2003 to a high of 76% in 2004. When all May sample sets off Barrow were combined (1985, 1986, 2003, 2004), there was a significant difference (t‐test, P < 0.004) between the proportion of muddy juveniles to the proportion of muddy adults, with muddy adults being more common. The Barrow area was a commonly used feeding ground during migrations in both the spring (61% of the sample were feeding; 55% epibenthically) and autumn (99% of the sample; 97% epibenthically). Bowheads both migrate and feed through areas where petroleum extraction is underway and anticipated; hence, exposure to oil after a spill is of considerable concern to Native communities and management agencies.