Foraging ecology and spatial behaviour of the red fox (Vulpes vulpes) in a wet grassland ecosystem

We investigated diet composition, habitat selection and spatial behaviour of the red fox (Vulpes vulpes) in relation to the availability of wader nests in a coastal polder area in southwest Denmark. The predatory role of the red fox in wet grassland ecosystems has profound implications for conservation status of declining populations of grassland breeding waders. However, few studies have focussed on the foraging ecology and behaviour of the red fox in these landscapes. Faecal analyses revealed that fox diet consisted of birds (43 % of prey remains?/?32 % of biomass), rodents (39 %?/?21 %), sheep (mainly as carrion, 14 %?/?41 %) and lagomorphs (4 %?/?7 %). Charadriiformes (including waders) comprised 3–12 % of prey remains throughout the year. Telemetry data and spotlight counts indicated that foxes did not select areas with high densities of breeding waders, suggesting that foxes did not target wader nests while foraging. Foxes maintained stable home ranges throughout their lives, indicating that the area sustained a permanent fox population all year round. The population densities, estimated from spotlight surveys, were 0.74 visible foxes km^?2 (95 % CI; 0.34–1.61) on the preferred breeding habitat for waders and 1.21 km^?2 in other open habitats such as cultivated fields. Our results indicate that red fox predation on wader nests is incidental, consistent with the notion that red foxes are generalist predators that opportunistically subsist on many prey groups.     

WEIGHT AND CULMEN CHANGES IN

Summers, R.W. &; Kaletja-Summers, B. 1996. Seasonal use of sandflats and saltmarshes by waders at low and high tide at Langebaan Lagoon, South Africa. Ostrich 67:72-79.

Migrant and resident waders were counted on sandflats and saltmarshes at low and high tide during two summers (197576 and 1976–77) and two winters (1975 and 1976) at Langebaan Lagoon. Intertidal sandflats supported higher densities of waders than saltmarshes at low tide in summer (18.7 and 17.2 waders ha' on sandflats compared with 0.4 and 2.9 waders ha' on saltmarshes) and winter (0.9 and 3.1 compared with 0.6 and 1.9 waders ha I for the two years). At high tide, most waders moved onto saltmarshes, attaining densities of 70.4 and 53.6 waders ha' in the two summers, and 5.7 and 15.6 birds ha' in the two winters. Resident waders comprised 0.3 and 0.8% of the wader community in the two summers and 41 and 5% in the two winters. They were also at higher densities in winter than in summer. The composition of wader communities on the different sandflats varied little in summer and Curlew Sandpipers were the most abundant species on all sandflats. Minor variations in species composition included proportionately more Turnstones at the mouth of the lagoon, more Sanderlings and Whimbrels in the mid sections and more Terek Sandpipers, Greenshanks and Curlews in the upper part. Larger percentages of waders were foraging on the sandflats at low tide in both summer (96 and 92% for the two summers) and winter (85 and 94% for the two winters) compared with the saltmarshes (73 and 79% in the two summers and 60 and 81% in the two winters). A larger proportion of small waders were foraging on sandflats at low tide compared with large waders. At high tide on the saltmarshes, the percent of foraging birds was lower in summer (29% for both summers) than in winter (36 and 78% for the two winters), perhaps reflecting seasonal changes in energy requirements.     

Sharing habitat: Effects of migratory barnacle geese density on meadow breeding waders

• 1.Following targeted conservation actions most goose populations have increased. The growing goose populations caused an increase in human-wildlife conflicts and have the potential to affect nature values. As meadow birds, including meadow-breeding waders, were declining throughout Western Europe, the possible negative effect of rising numbers of foraging barnacle geese on their breeding success has been questioned.
• 2.We used GPS-transmitter data to measure the density of foraging barnacle geese during daylight hours. Using dynamic Brownian Bridge Movement Models (dBBMM), we investigated the effect of barnacle goose density on the territory distribution of five wader species, and on nest success of the locally common Northern lapwing. We used model selection methods to identify the importance of barnacle goose density related to other environmental factors.
• 3.Our results showed an insignificant positive association between barnacle goose density and nest territory density of the Northern lapwing and common redshank. Barnacle goose density had no influence on territory selection of godwit, oystercatcher and ringed plover. We did, however, find a negative correlation between barnacle geese density and the nest success of the Northern Lapwing.
• 4.We infer that either barnacle goose foraging leads to improved territory conditions for some wader species, or that both barnacle geese and waders prefer the same type of habitat for foraging and nesting. Higher barnacle goose density was correlated with fewer Northern lapwing nests being successful.
• 5.Synthesis and application: Experimental research is needed to disentangle the causal chain, but based on our observational findings, we suggest to increase water logging that may attract both barnacle geese and wader species. Further investigation on the effects of barnacle geese on wader species is necessary to identify the cause of the negative correlation between barnacle geese density and nest success of lapwings; nest protection experiments could give further insight.

     

Managing coastal grasslands for an endangered wader species can give positive results only when expanding the area of open landscape

The rapid loss of wetlands during the 20^th century has caused a severe decline in the biota associated with these habitats. In Europe, the loss of wet grasslands has seriously affected breeding waders, whose numbers have halved in the past 50 years and remaining populations are facing fragmented, low quality habitats. To improve the remaining sites as breeding grounds for these birds, the exact habitat requirements of the species need to be known. Our study was carried out in Boreal Baltic coastal grasslands in Estonia, where land abandonment has been the main reason behind waders’ population declines in the past decades. Hence, we focus on partially overgrown fields, aiming to ascertain habitat characteristics determining the breeding site selection of meadow birds, especially the endangered Southern Dunlin (Calidris alpina schinzii).We studied the breeding site selection of four wader species (Southern Dunlin, Common Redshank (Tringa totanus), Northern Lapwing (Vanellus vanellus) and Common Snipe (Gallinago gallinago)) in 23 coastal grasslands over two years. We analysed seven habitat characteristics which could influence the breeding habitat selection of these species.Our study demonstrates that breeding sites of all studied wader species are located closer to wet areas and coastline and further away from woodland. Also, the height of the ground level has an impact on the breeding probability, with lower areas favoured. Concerning the Southern Dunlin, our results show that on sites where the species was absent, suitable breeding sites, regarding the distance from woodland edge, were absent. Thus, reforestation of grasslands may be the key reason behind the poor population status of the species. We also demonstrated that proximity of reed beds did not influence the breeding site selection of waders – a result which contradicts current wet grassland management suggestions.Expanding the open landscape, maintaining a large quantity of wet features suitable for foraging and preventing overgrowth of coastline and lower parts of the meadow makes the habitat optimal for breeding waders. Concerning the growth of the population size and spatial distribution of the Southern Dunlin, removal of woodlands adjacent to grasslands is crucial.     

洪泽湖冬春季鱼塘生境中鹬类群落特征与栖息模式

2005年冬季和2006年春季及冬季对洪泽湖东部湿地自然保护区内淮河入洪泽湖河口处(33°06′~33°07′N,118°29′~118°30′E)人工鱼塘生境中鹬类群落进行了研究。设置了4个样地,总面积157hm2。共记录到鹬类19种,其中冬季10种,春季15种。从数量上看,冬季鱼塘中的鸟类总数量远大于春季。在冬春季滞留期间,鹬类种群数量变动比较剧烈,反映了其迁徙集中的特点。鹬类主要在鱼塘生境中休息和觅食,对鱼塘内泥滩和浅水区小生境利用率最高。洪泽湖地区的鱼塘生境和渔业方式使鱼塘成为鹬类冬、春季的重要栖息地。     

Disturbance does not have a significant impact on waders in an estuary close to conurbations: importance of overlap between birds and people in time and space

Disturbance of wildlife is a potential cause of conservation concern, not least to overwintering waders Charadrii inhabiting estuaries close to conurbations where human recreational and economic activities are often concentrated. Disturbance from people on and alongside intertidal foraging areas could make it more difficult for birds to survive until spring in good condition by reducing the time available for foraging, increasing energy requirements and displacing birds to poorer foraging areas. We adopted a two-part approach to testing whether such significant impacts occurred in a Special Protection Area where disturbance risk was high because of its small size and close proximity to conurbations. In part one, we recorded over the whole estuary during stages of the tidal cycle when part or all of the intertidal zone was exposed and so accessible to waders (i.e. on receding, low and advancing tides): (1) the numbers and activities of people on the intertidal flats and on the adjacent land in those places where people were visible to waders in the intertidal zone and (2) the numbers of waders present and disturbed into flight, the flight distance and flight duration in the ‘overlap’ areas where people did disturb waders. People occurred on < 25% of the 938 ha of intertidal flats, but most waders foraged on mudflats, whereas most people were on sandflats. People on land were visible to foraging waders along < 35% of the 16.5 km of shoreline. Waders and people were therefore substantially separated in space. Within overlap areas, people and waders were often frequently separated in time: for example, people on land mostly disturbed waders when only the upper shore levels were exposed. The average overwintering wader spent < 0.1% of its foraging time during daylight flying away from people and the additional energy expenditure was equivalent to < 0.02% of its daily requirements. The comparison made in part two between our study area and two comparable estuaries showed that the number of visits each day to the overlap areas would need to be 29 or 43 times greater for disturbance to have lowered the birds’ body condition and winter survival. Both parts of the study therefore suggested strongly that the amount of disturbance was too trivial to have a significant impact on waders. It is concluded that: (1) to properly assess disturbance risk to waders, both extensive and intensive observations must be made on the behaviour of people and birds to quantify the extent to which they overlap in space and time, and (2) it should not be assumed that an estuary's close proximity to conurbations, and the presence of large numbers of people in the vicinity of the SPA, necessarily implies a significant disturbance risk to waders.     

High water roost selection by waders: maximizing feeding opportunities or avoiding predation?

During the highest spring tides the intertidal sediment flats of estuaries are fully inundated at high water, and waders have no choice but to move to supratidal roosts, e.g. on open farmland, saltpans or beaches. However, in many estuaries during the lowest neap or intermediate tides there are sectors of upper intertidal sediment flats that remain exposed even at the peak of high water, and so waders have the choice of roosting either there or in supratidal sites. In the Tagus Estuary, Portugal, as elsewhere, waders use both types of roosts during high water. Our main objective was to understand what makes waders opt for one of these two types of available roosts. We monitored wader use of saltpans and intertidal roosts from spring to neap tides, and measured foraging and alarm behaviour, prey availability and disturbance by predators. Most of the wader species studied chose intertidal (mudflat) roosts whenever these were available, and only roosted in saltpans during the peak of spring tides. We hypothesized that this preference was explained either by an attempt (i) to continue feeding into the high water period, or (ii) to minimize predation risk. Extending feeding time into the high water period did not seem to be very relevant for roost choice because both prey availability and foraging activity were low in both types of roosts. However, predator disturbance was several times higher in the saltpans than in the intertidal roosts, suggesting that this factor may be the determinant in the choice of roost type.     

Radar remote sensing as a novel tool to assess the performance of an agri-environment scheme in coastal grasslands

Coastal grasslands are semi-natural habitats used for agriculture, but they are also vital habitats for many taxa, such as waders. The importance of this habitat for wildlife has found recognition in the policies of the European Union, resulting in the implementation of biodiversity-friendly agri-environment schemes (AES) to ensure the sustainable management of these areas. However, the performance of AESs has often been questioned and data to analyse their effectiveness is mostly lacking.To fill this knowledge gap, we used freely available European Space Agency's Sentinel-1 Synthetic Aperture Radar (SAR) images and ground truth data to describe the vegetation height based habitat suitability of coastal grasslands as breeding sites for waders at a country-wide scale in Estonia, where the main threat to this habitat is overgrowing with high sward plant species.We show that satellite remote sensing can be used as a straight-forward and reliable tool to estimate the grazed coastal grassland habitat suitability for breeding waders in terms of vegetation height in two broad classes.We demonstrate that the AES applied on Estonian coastal grasslands is important for improving the suitability of this habitat for the breeding wader community: compared to 24% of suitable habitat in areas where no agricultural subsidies are paid, 60% of the land under the targeted AES is suitably managed for breeding waders. The highest proportion of habitat suitability (76%) is achieved in areas receiving targeted top-up subsidy for wader conservation.Continued monitoring of the performance of the AES is essential for taking timely and targeted conservation actions and we strongly recommend the wider use of remotely sensed data for this purpose. We promote the continuation of the AES scheme applied on Estonian coastal grasslands while improving its efficiency through carefully raised stocking rates and increased uptake of the top-up scheme.     

WADERS (CHARADRII) AND OTHER WATERBIRDS AT LANGEBAAN LAGOON,SOUTH AFRICA, 1975–1986

Summary

Underhill, L. G. 1987. Waders (Charadrii) and other waterbirds at Langebaan Lagoon, South Africa, 1975–1986. Osrrich 58: 145–155.

Langebaan Lagoon was surveyed for waterbirds at midsummer and midwinter between 1975 and 1986. The median number of birds counted in summer was 37 500, of which 34 500 were waders (93% of the waders being Palaearctic migrants). Curlew Sandpiper (59,2%), Grey Plover (10,5%), Sanderling (8,3%), Knot (8,1%) and Turnstone (5,7%) were the major components of the summer wader population. The median number of birds in winter was 10 500, of which 4500 were flamingos and 4000 waders. For Palaearctic waders, the median winter population was 11,5% of the median summer population, but varied between 2,5% and 30,1%. For species of wader which breed in the Taimyr Peninsula, Siberia, a three-year cycle in the numbers of birds overwintering was detected, with large numbers in 1977, 1980, 1983 and 1986. Birds feeding on invertebrates consumed 126,9 kJ m^?2 yr^?1, or 24% of the total production of invertebrates. Greater Flamingos have a major impact on energy cycling at Langebaan Lagoon, accounting for 73,3% of the winter energy consumption by the avifauna. Langebaan Lagoon is the most important wetland for waders in South Africa, accounting for about 10% of the coastal wader population of South Africa. At midsummer, about 0,5% of the total wader population of the East Atlantic Flyway is at Langebaan Lagoon, which ranks about 20th in importance for waders on the flyway.     

Variation in numbers and behaviour of waders during the tidal cycle: implications for the use of estuarine sediment flats

Estuarine sediment flats are essential feeding areas for waders, but their exploitation is constrained by the movements of tides. In this cyclic environment the exposure period of sediment flats decreases several fold from upper to lower flats, and the moving tidal waterline briefly creates particular conditions for waders and their prey. This study attempts to determine how the exposure period and the movement of the tide line influence the use of space and food resources by waders across the sediment flats. Wader counts and observations of feeding behaviour were carried out in all phases of the tidal cycle, in plots forming a transect from upper to lower flats, thus representing a gradient of exposure periods. Pecking, prey intake, and success rates varied little along the gradient. Some species actively followed the tide line while foraging, whereas others are evenly spread over the exposed flats. Black-tailed Godwit, Dunlin and Avocet were 'tide followers', whereas Grey Plover, Redshank and Bar-tailed Godwit were 'non-followers'. Densities of 'followers' near the tide line were up to five times higher than elsewhere. Species differed markedly in the way they used space on the flats, but in general the rate of biomass acquisition (in grams of ash-free dry weight per time exposed) was much higher in lower flats. However, this preference was insufficient to counter the much longer exposure of the upper flats, so the total amount of biomass consumed on the latter was greater. Therefore, it was in these upper flats that waders fulfilled most of their energetic needs. Consequently, upper flats are of particular importance for the conservation of wader assemblages, but because they are usually closer to shore they tend to suffer the highest pressure from disturbance and land reclamation.     

Modeling foraging behavior of piping plovers to evaluate habitat restoration success

Habitat restoration projects are often deemed successful based on the presence of the target species within the habitat; however, in some cases the restored habitat acts as an ecological trap and does not help to improve the reproductive success of the target species. Understanding wildlife–habitat relationships through precise measurements of animal behavior can identify critical resources that contribute to high quality habitat and improve habitat restoration practice. We evaluated the success of a restored piping plover (Charadrius melodus) breeding habitat in New Jersey, USA. We identified the major factors influencing foraging rates, compared foraging activity budgets over 3 yr at restored and natural habitats, and explored the potential of artificial tidal ponds as a viable restoration alternative. Adult foraging rates were higher in artificial pond and ephemeral pool habitats, during low tide, and after breeding activity ended. Adult foraging rates were impeded by the presence of people and vehicles within 50 m. Chick foraging rates were highest at artificial ponds and bay shores and lowest in dunes and on sand flats. Chick foraging rates were strongly hindered by the presence of corvids and the number of people within 50 m. In addition, at artificial tidal ponds, piping plovers spent more time foraging and less time engaged in defensive behaviors (vigilance, crouching, and fleeing) compared to other potential habitats. Our findings support the hypothesis that artificial tidal ponds are a valuable, perhaps superior, foraging habitat. Future beach restoration projects should include this feature to maximize habitat quality and restoration success. © 2011 The Wildlife Society.     

Changes in the waterbird populations of the Oosterschelde (SW Netherlands) as a result of large-scale coastal engineering works

Between 1982 and 1987, the construction of a storm-surge barrier and two secondary dams in the eastern and northern parts of the Oosterschelde/Krammer-Volkerak area resulted in the loss of 33% of the 170 km² of intertidal area in the estuary. Consequences for non-breeding waterbirds were evaluated on the basis of monthly high-tide counts during five seasons before and three seasons after the construction period.In the entire Oosterschelde/Krammer-Volkerak area, numbers of wintering waders decreased but those of ducks increased. Peak numbers and total number of bird-days changed little, but the seasonal pattern shifted from a midwinter maximum to a peak in autumn.In the Oosterschelde (excluding the Krammer-Volkerak), where 17% of the tidal flats disappeared, species feeding mainly on open water remained stable or increased. Species dependent on intertidal areas for foraging (mainly waders and dabbling ducks) generally decreased. Total density of intertidal foragers decreased slightly. In most intertidal species, the Oosterschelde wintering population showed a stronger decrease, or smaller increase, than was shown during the same period by numbers in Britain and Ireland which were taken as an index of the total W-European winter populations. Changes varied considerably between species, and were correlated with their distribution within the estuary. Species concentrated in the eastern sector, where most habitat loss occurred, declined more than species with a more westerly distribution.Results indicate that intertidal foragers forced to move from the enclosed parts of the estuary were not generally able to settle into the remaining intertidal areas. Both dispersal to adjacent areas (mainly by dabbling ducks) and mortality during severe winter weather (in some wader species) may have contributed to the declines. Populations of intertidal foragers apparently were (and consequently still are) close to carrying capacity, and further changes in capacity, as foreseen from geomorphological changes still under way in the estuary, are likely to be reflected in bird populations.Numbers of waders moulting in the Oosterschelde in late summer declined strongly compared to numbers in other seasons. Increased disturbance due to recreational activities may have played a role during this time of the year.     

Water depth selection, daily feeding routines and diets of waterbirds in coastal lagoons in Ghana

Water depth requirements, diet, feeding styles and diurnal activity patterns are described for waterbirds using two brackish water lagoon systems in coastal Ghana, the Songor and Keta Lagoons. We project the habitat and activity data on a guild structure defined on the basis of individual feeding style and the sensory mechanism used to detect food. A total of 3199 flocks containing 118,648 individuals of 36 different waterbird species were examined during October-November 1994. Feeding habitats varied from dry mudflats to wet mud and shallow water of not more than 20 cm. The depth of water selected by waterbirds for foraging (but not for roosting) was correlated with tarsus length. Foraging birds exhibited a wide range of feeding styles using visual and/or tactile means for detecting prey: pecking, probing, stabbing, sweeping and ploughing, sometimes feeding singly, communally or socially in loose or dense flocks. Prey items taken ranged from seeds of Widgeongrass Ruppia maritima to invertebrates (mainly polychaetes, molluscs and crabs) and fish, mainly juvenile Tilapia. The daytime was spent on two main activities, feeding and roosting, with a small fraction of the time (average of 10% for 25 species) spent on comfort activities. The waterbirds exhibited either a circadian (most waders, except Common Sandpipers Actitis hypoleucos and Turnstones Arenaria interpres) or a diurnal foraging activity pattern (herons and terns), with no purely nocturnal species. Some species fed throughout the day, others showed peak foraging at various times of the day. The proportion of time spent foraging was related to guild (highest in visual and tactile surfaceforaging waders) and was negatively correlated with the size of the species. We conclude that the observed patterns in the use of the 24-h day by waterbirds for foraging are not species specific but vary depending on conditions on the feeding grounds. Nocturnal foraging is a normal and a regular strategy used by waterbirds to obtain enough food to fulfill their energetic requirements, so that irrespective of the sensory mechanism used to detect prey and the conditions prevailing on the feeding grounds, waterbirds forage day and night as dictated by their energetic needs. Water depth appears to be the key environmental factor controlling the availability of food for the waterbirds in the Ghanaian lagoons.     

Effects of endogenous rhythms and light conditions on foraging and predator-avoidance in juvenile plaice

The influences of a light: dark cycle and a persistent endogenous rhythm of activity on foraging (on the bivalve Donax vittatus ) and avoiding a predator (juvenile cod, Gadus morhua ) were investigated in freshly-caught juvenile plaice, Pleuronectes plalessa . Time lapse video recordings were made of fish in the presence and absence of prey and predators in laboratory tanks over 24-hour periods between the times of successive daytime low waters. Endogenous rhythms of activity were seen in all experimental treatments. Swimming both close to the bottom and in the water column showed a strong circatidal rhythm, with most activity 2 to 3 h after the predicted time of high water. Swimming in the water column was more frequent at night than by day. In the presence of a population of Donax , whose siphon tips could be eaten as food, swimming close to the bottom became more frequent. This increase in benthic swimming was independent of the endogenous cycle of activity and was correlated with the frequency of attacks on siphons. The presence of the cod predator delayed the onset of foraging activity, producing a foraging/predator avoidance trade-off. The independence of foraging from light and endogenous rhythms suggests that this trade-off may be similarly independent. The cod also greatly reduced swimming in the water column in darkness, behaviour apparently unrelated to foraging.     

Predation on wader nests in Europe

The population declines of waders in Europe are widely considered to have resulted from habitat loss and degradation due to agricultural changes. However, recent empirical evidence suggests that levels of predation on wader nests are unsustainably high in many cases, even in some situations where breeding habitat is otherwise favourable. We review the published and 'grey' literature on nest predation on waders in Europe and quantify the relative importance of the major predators. Nest cameras offer the least biased method of identifying and quantifying nest predators. A small number of camera studies, in combination with others utilizing nest temperature loggers, indicate that nocturnal/mammalian predators make the largest contribution to wader nest predation. More than half of site-years or studies reviewed reported clutch failure rates of over 50% attributable to predation alone, a rate that is likely to be associated with declining populations, although parameters such as chick and adult survival will also affect population trends. Correlates of wader nest predation are documented, with time of season, field type and management, distance to habitat/field edge, wader nest density, and abundance of mammalian predators being most consistently identified. Future directions of research into wader productivity are discussed, and we suggest that studies quantify additional life-history parameters such as chick survival, as well as examining the predator community, wherever possible.     

Synergies between site protection and agri‐environment schemes for the conservation of waders on lowland wet grasslands

Two conservation strategies have been put in place in Europe to address precipitous population declines of wading birds that breed on lowland wet grasslands. These are site protection and agri‐environment schemes (AESs) and the two are rarely compared, or their synergy assessed. Increasingly, efforts to recover populations of previously widespread species follow a landscape‐scale approach whereby habitat improvement takes place at key sites through partially overlapping protected area management and AESs. To investigate whether site protection and AESs improve the conservation status of breeding waders and how these interact, we partially repeated a 2002 survey of breeding waders on protected areas (nature reserves and Sites of Special Scientific Interest) and sites with wader‐specific AES options in England in 2009 and 2010. We then assessed the individual and combined effects of these delivery mechanisms on field occupancy, breeding density and population change of four species of declining wader (Northern Lapwing Vanellus vanellus, Common Snipe Gallinago gallinago, Eurasian Curlew Arquata numenius and Common Redshank Tringa totanus). Although results for Curlew differed from the other species, in general field occupancy was positively influenced by conservation delivery mechanisms, with the highest occupancy and breeding densities on land where site protection was combined with wader‐specific AES options. Field occupancy varied between different types of AES, with higher occupancy associated with higher‐level options in fields, particularly those on nature reserves. Outside nature reserves, the history of AES management did not influence wader populations, but within nature reserves and on fields that gained AES management between 2002 and 2009–2010, populations of Curlew and Snipe were more likely to have persisted and population change in Snipe and Lapwing was more positive. We conclude that the conservation of breeding waders will be most effective when site protection and AES management are combined on the same land. Using limited AES money to support management for breeding waders on, around and between the existing network of protected sites will protect remaining populations while presenting opportunities for population expansion in future.     

The mechanisms of interference competition: two experiments on foraging waders

Models of population dynamics that include interference competitionhave often been applied to foraging waders and less so to otherforagers, even though these models are, in principle, generallyapplicable. At present, however, it is still unclear whetherinterference competition is of importance for foraging waders.To support this idea experimental evidence and knowledge ofthe mechanisms underlying interference effects are required.We experimentally determined the relationship between foragerdensity and foraging success in two wader species: the red knot(Calidris canutus) and the ruddy turnstone (Arenaria interpres).With each of the two species, we conducted an experiment consistingof 300 one-min trials. In these trials we scored the behaviorand the foraging success of focal individuals at specific combinationsof bird and prey density. Irrespective of prey density, individualsof both species discovered fewer prey items at higher bird densities.Despite this, only in turnstones did intake rates decline withincreasing bird density. Knots compensated for a lower prey-discoveryrate by rejecting fewer prey items at higher bird densities.In knots, bird density had a complex, nonmonotonic effect onthe time spent vigilant and searching. In turnstones the maineffect of increased bird density was a reduction in the prey-encounterrate, that is, the reward per unit search time. Effects on thetime spent vigilant and the time spent searching were less pronouncedthan in knots. Thus, the mechanistic basis of the effects ofbird density was complex for each of the two species and differedbetween them.     

Plasticity of Hamster Circadian Entrainment Patterns Depends on Light Intensity

The multiple oscillatory basis of the mammalian circadian pacemaker is adduced by, among other phenomena, the occurrence of split locomotor activity rhythms in rodents after prolonged exposure to constant light. More recently, split rhythms entrained to a 24h light:dark:light:dark cycle have been documented following scheduled access of hamsters to a novel running wheel or by photoperiod manipulations alone. Because the incidence of constant light-induced splitting depends on light intensity, the role of this variable was assessed in this new splitting paradigm. Male Syrian hamsters, entrained to a 14h light:10h dark cycle, were transferred to individual running wheel cages 7h after light onset. Transfer coincided with the beginning of the scotophase of a new photocycle alternating between 5h of relative dark and 7h of light. For four weeks bright photophases (～350 lux) were alternated with either dim (<0.1 lux) or completely dark (0 lux) scotophases. An additional group received moderate intensity photophases (～45 lux) paired with dim scotophase illumination. For an additional four weeks, all hamsters were exposed to the same bright:dim light:dark cycle. Dim light in the scotophase significantly increased the incidence of split activity rhythms relative to that observed with completely dark scotophases. Overall wheel-running rates and activity induced by a cage change were also increased in dim light-exposed animals. Group differences largely disappeared four weeks later when hamsters previously maintained in completely dark scotophases were exposed to dim scotophases. Photophase light intensity did not affect the overall incidence of splitting, but influenced the timing of activity in the afternoon scotophase. The effects of dim illumination may be mediated in part via enhanced locomotor responses to transfer to a new cage or by changes in coupling interactions between component oscillators.     

Effect of circadian on the activities of ion transport ATPases and histological structure of kidneys in mice

The impacts of unnatural every day cycles (circadian) for 60 days on the histological structure of kidneys and ATPase activities in MF1 mice were studied. The exposure times were 16 h dark, 16 h light, 24 h dark, and 24 h light, and control exposure times were 12 h dark followed by 12 h light. Our results showed an increase in the total ATPase activity of mice in all groups. Additionally, the activity of the enzyme Na⁺/K⁺-ATPase was increased after 24 h darkness, 24 h light, and 16 h light exposures compared to control. The enzyme Mg⁺²-ATPase activities of the groups were higher when exposed to 16 h light, 24 h light, 24 h darkness and 16 h darkness. The activities of total ATPase, Na⁺/K⁺-ATPase and Mg⁺²-ATPase in kidneys were increased in all groups after 24 h light, 24 h darkness, 16 h darkness and 16 h light exposures. Interestingly, the activity of V-type ATPase was reduced after 16 h darkness, 24 h darkness and 16 h light. Taking everything into account, changes in the day by day cycle prompt neurotic changes, enzymatic and histological changes in the kidneys of mice. More studies should be directed to explore the impacts of light and darkness that can prompt these progressions.     

Photoperiod affects growth, behaviour and stress variables in Clarias gariepinus

Short periods of light or no light (18D : 06L and 24D : 00L) resulted in an increased growth compared to extended periods of light (06D : 18L and 12D : 12L) in African catfish Clarias gariepinus . Fish under longer periods of light (12D : 12L and 18D : 06L) showed higher swimming activity, more aggression (injuries on the body) and higher lactate, free fatty acids and cortisol levels compared to those who were reared at shorter periods of light (24D : 00L and 18D : 06L). Feeding activity during light and dark periods in this experiment showed that C. gariepinus had both night and day feeding activities, with a preference to diurnal feeding in the 12D : 12L photoperiod. The results showed that light plays an important role in the African catfish behaviour and its well‐being. As the hours of light increased during the 24 h cycle, data suggests that the fish were more stressed and aggressive, compared to those under a reduced number of light hours.