Diets of shorebirds at the berg river estuary, south africa: spatial and temporal variation
TL;DR: Kalejta et al. as mentioned in this paper studied the diets of three common migrant waders; Curlew Sandpiper Calidris ferruginea, Grey Plover Pluvialis-squatarola and Greenshank Tringa nebularia and three resident species, Blacksmith Vanellus armatus, Kittlitz's Charadrius pecuarius and Whitefronted Plovers C. marginatus.
Abstract: Summary Kalejta, B. 1993. Diets of shorebirds at the Berg River estuary, South Africa: spatial and temporal variation. Ostrich 64: 123–133. The diets of three common migrant waders; Curlew Sandpiper Calidris ferruginea. Grey Plover Pluvialis-squatarola and Greenshank Tringa nebularia and three resident species, Blacksmith Vanellus armatus, Kittlitz's Charadrius pecuarius and Whitefronted Plovers C. marginatus, were studied at the Berg River estuary, South Africa from December 1987 to April 1989. Direct observations of feeding were combined with analyses of stomach contents, pellets and droppings. Nereid worms, Ceratonereis erythraeensis and C. keiskama, were the principal food of all species studied except Greenshanks, which fed mostly on crabs, Hymenosoma orbiculare. Despite considerable overlap in the diets of all bird species, there were differences in the size classes of nereids taken by different bird species. Visually-foraging plovers (Charadriidae) were highly selective, feeding on the largest nere...
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TL;DR: In this article, the authors evaluated salinas as feeding habitats relative to natural intertidal habitats by comparing time spent foraging, prey-size selection, and net energy intake rate of four overwintering small-sized shorebird species on inter-tidal mudflats and on adjacent salinas.
Abstract: Because many natural waterbird habitats are threatened by human disturbance and sea level rise, it is vitally important to identify alternative wetlands that may supplement declining natural habitats. Coastal salinas are anthropogenic habitats used for obtaining salt by evaporation of sea water. These habitats support important numbers of waterbirds around the world, but their importance as feeding habitats is poorly understood. I evaluated salinas as feeding habitats relative to natural intertidal habitats by comparing time spent foraging, prey-size selection, and net energy intake rate of four overwintering small-sized shorebird species on intertidal mudflats and on adjacent salinas. In winter, Dunlin Calidris alpina, Curlew Sandpiper C. ferruginea and Sanderling C. alba predominantly used the mudflats, whereas Little Stint C. minuta fed mainly on the salina. In the pre-migration fattening period, all species preferred to feed on the salina, significantly increasing the time they spent feeding in the supratidal pans. Net energy intake rates (kJ min−1) were significantly higher on the salina than on the intertidal mudflats in 60% of all comparisons. On average, salina contributed 25.2 ± 24.2% (range: 4–54%) of the daily consumption in winter and 78.7 ± 16.4% (range: 63–100%) of the daily consumption in the pre-migration period. I recommend that modern active salinas maintain flooding conditions in the evaporation pans throughout winter, thus increasing the available surface for foraging waterbirds. I conclude that the conservation of salinas at coastal wetlands is a viable approach for shorebird conservation.
134 citations
Cites background from "Diets of shorebirds at the berg riv..."
...Overall, small-sized calidrids prefer soft-bodied polychaetes to hard-shelled species, because of the more favourable rate at which their energy can be processed (Kalejta 1993; Zwarts and Wanink 1993)....
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TL;DR: The availability of supratidal foraging habitats seems to contribute significantly to the maintenance of the population of overwintering Redshanks, and energy intake in this habitat contributed 23% and 82% of the total daily energy requirement in winter and the pre-migration period, respectively.
Abstract: The prey-size selection, foraging behavior, and intake rate of overwintering Redshanks (Tringa totanus) were studied in a supratidal-intertidal system with high intertidal densities of shorebirds (100 birds ha−1). For assessing the importance of the energy obtained in the supratidal habitat (saltworks), daily consumption in this habitat was compared with the total daily energy requirement. Redshanks passively select prey within a certain size range from those accessible on the intertidal area. Despite the high prey biomass on the mudflats, Redshanks exhibited a low intake rate during winter (0.321 kJ min−1). This low intake seems to be related to the influence of the high densities of foraging shorebirds on the behavior of prey. Although intake rate was higher in the saltworks, the majority of Redshanks did not choose to feed there in winter. This foraging pattern seems to be related to density-dependent effects in habitat occupancy, as social interactions could have kept Redshanks out of the sal...
92 citations
Cites background from "Diets of shorebirds at the berg riv..."
...The mean daily intake rate in February was low, which could explain why Redshanks ate more Hydrobia than Nereis (Hydrobia have a high shell:flesh ratio, and soft-bodied Nereis would logically be, in general, the preferred prey; Kalejta 1993)....
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TL;DR: Results show that foraging strategies may play important roles in shorebirds’ habitat use in intertidal areas, and two life forms of macrobenthos was similar in the transitional zones between the salt marshes and the bare flats.
Abstract: Dense flocks of migratory shorebirds from diverse species often concentrate in the intertidal areas for stopover. Trophic structure, food partition, prey availability and selectivity, predation risk, and abiotic factors are often used to explain the differences in habitat use of coexisting shorebirds. We sampled the macrobenthos and surveyed the distribution of shorebird populations to study the effects of foraging strategies on the habitat use of shorebirds at Chongming Dongtan, an important stopover site for shorebirds on the East Asian–Australasian Flyway. Results show that the relative abundance of epifaunal macrobenthos in salt marshes was much higher than that in the bare flats, whereas the relative abundance of infaunal macrobenthos in salt marshes was much lower than that in bare flats. The relative abundance of two life forms of macrobenthos was similar in the transitional zones between the salt marshes and the bare flats. Shorebirds with different foraging strategies exhibited different habitat uses. Pause-travel shorebirds mainly utilized the salt-marsh fringes, while tactile continuous shorebirds relied heavily on the bare flats. There was no significant difference in habitat use for visual continuous shorebirds. The density of tactile continuous shorebirds was positively correlated with bivalve density, and that of visual continuous shorebirds positively with crustacean density. Meanwhile, the relative abundance of pause-travel foraging shorebirds was positively correlated with the relative abundance of epifaunal, but negatively with infaunal macrobenthos. In contrast, the relative abundance of tactile foraging shorebirds had a positive correlation with infaunal but a negative one with epifaunal life form. Therefore, foraging strategies may play important roles in shorebirds’ habitat use in intertidal areas.
69 citations
Cites background from "Diets of shorebirds at the berg riv..."
...Differences in foraging strategy account for the variation in vigilance rate, flock size (Barbosa 1995, 1997), diversity of prey types (Turpie and Hockey 1997), and prey size (Kalejta 1993) of shorebirds....
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...…structure (Schoener 1965), food partition (Davis and Smith 2001), prey availability (McNeil et al. 1995; Hubbard and Dugan 2003) and selectivity (Kalejta 1993; Backwell et al. 1998), predation risk (Cresswell 1994; Ydenberg et al. 2002), and abiotic factors (Burger 1984) are often used to…...
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25 Nov 2016
Abstract: Tidal range is a master factor governing the differences in physico-chemical and biological characteristics between microtidal ( 2 m) estuaries, which, for convenience, thus include mesotidal estuaries (2–4 m). Microtidal estuaries differ from macrotidal estuaries in geomorphology, tidal water movements, salinity regimes, residence times, turbidity, sedimentology and intertidal area. Consequently, their phytoplankton, microphytobenthos and macrophytes communities differ in biomass and production, areal extent, distribution patterns and composition. Mesozooplankton comprise predominantly autochthonous species in microtidal estuaries and allochthonous species in macrotidal estuaries. Meiobenthos in microtidal estuaries have greater densities in subtidal than intertidal areas and species persist along the estuary. Macrobenthos is dominated by small deposit-feeding species in microtidal estuaries, whereas macrotidal estuaries contain some larger species and suspension feeders. Species richness and abundance of estuarine-resident fish species and the contributions of diving piscivorous birds and wading invertebrate-feeding birds are greater in microtidal estuaries. As paradigms regarding estuarine ecology have been based mainly on northern hemisphere macrotidal systems, this review has redressed this imbalance by detailing the extent of differences between microtidal and macrotidal estuaries. In particular, it uses data and case studies for southern hemisphere microtidal systems to demonstrate that the physico-chemical characteristics and ecology of the main flora and fauna of microtidal estuaries are frequently not consistent with those paradigms.
61 citations
TL;DR: Energy intake rates of Grey Plovers were very consistent across the estuary, suggesting that individuals occupy or defend areas which provide access to comparable food resources, and Curlew Sandpipers may use neighbour success rates in selecting foraging sites.
Abstract: Foraging densities of Curlew Sandpipers Calidris ferruginea and Grey Plovers Pluvialis squa-tarola at the Berg River estuary, South Africa, are examined in relation to prey and habitat attributes.
There is a substantial overlap in the prey species eaten by Curlew Sandpipers and Grey Plovers, but the distribution patterns of the two species within the estuary could not be explained by the same prey attributes.
The distribution of tactilely foraging Curlew Sandpipers was determined largely by the numerical abundance of nereid worms. They foraged preferentialiy on muddy rather than sandy substrata, but their distribution could not be explained on the basis of substratum penetrability. The density of visually foraging Grey Plovers was correlated with the biomass, rather than abundance, of the larger of the two common nereids on the estuary. The favoured foraging area of Grey Plovers had a high vegetation cover, but their foraging dispersion was not influenced by substratum type.
The energy intake rates of Curlew Sandpipers were broadly inversely related to their foraging density, although the rate of prey capture was maximal at high prey density. These birds may use neighbour success rates in selecting foraging sites. Energy intake rates of Grey Plovers were very consistent across the estuary, suggesting that individuals occupy or defend areas which provide access to comparable food resources.
53 citations
References
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TL;DR: A graphical method is discussed which allows a specification of the optimal diet of a predator in terms of the net amount of energy gained from a capture of prey as compared to the energy expended in searching for the prey.
Abstract: A graphical method is discussed which allows a specification of the optimal diet of a predator in terms of the net amount of energy gained from a capture of prey as compared to the energy expended in searching for the prey. The method allows several predictions about changes in the degree of specialization of the diet as the numbers of different prey organisms change. For example, a more productive environment should lead to more restricted diet in numbers of different species eaten. In a patchy environment, however, this will not apply to predators that spend most of their time searching. Moreover, larger patches are used in a more specialized way than smaller patches.
4,132 citations
TL;DR: The address of the president of a society, founded largely to further the study of evolution, at the close of the year that marks the centenary of Darwin and Wallace's initial presentation of the theory of natural selection.
3,717 citations
TL;DR: The environmental conditions encountered during migration and the interactions with other individuals have evidently been important factors in the evolution of morphological and morphological differences among shorebird species.
Abstract: During migration, shorebirds form dense multispecific aggregations within rela- tively uniform and limited marine littoral habitats. The amount of available feeding space in the habitats frequented fluctuates widely with the daily and seasonal changes in the tidal rhythm. Shorebird species broadly overlap in their periods of peak abundance, inter- and intrahabitat distributions, and in the food organisms preyed upon. However, the totality of species differ- ences and the transient character of migratory assemblages apparently minimizes interspecific interactions that might result in competitive exclusion. The staggering of peak population densities and differences in distribution is most pronounced among morphologically similar species. The number of individuals and species that occur in an area is apparently determined by the amount of available feeding space and the physical diversity of the habitat. Food appears to be generally abundant relative to the requirements of the birds in all the habitats studied. The environmental conditions encountered during migration and the interactions with other individuals have evidently been important factors in the evolution of morphological and be- havioral differences among shorebird. species. Individuals must be as able to survive during the nonbreeding season as they are during the breeding season.
242 citations
TL;DR: This paper focuses on the diets and foodexploitation patterns of four widely sympatric sandpipers of the genus Calidris that breed regularly and abundantly near Barrow, Alaska, to describe diet and to examine degree of overlap.
Abstract: Most closely related sympatric bird species differ in their food-gathering structures, foraging techniques, and/or food preferences, with the result that they take different kinds of foods (Lack, 1954; Newton, 1967). Specialization in diet presumably evolves as a consequence of competition for limited food resources and is considered essential for continued coexistence (Lack, 1954; Mayr, 1963). This type of specialization also reflects the importance of food as an evolutionary factor in natural populations. We have found, however, that the diets of birds breeding on Arctic tundra overlap to a strikingly high degree. The circumstances behind this are straightforward: the overlap is a consequence of a limited taxonomic diversity of food sources and a relatively simple community structure. Neither of these appears to provide, in space or time, the range of opportunities permitting the variety of food specialization observed at temperate latitudes or farther south. The questions then arise, how can high arctic tundra such as that near Point Barrow, Alaska, support the variety and abundance of birds occurring there, and how do the birds' interact with regard to food supply? These are large questions that are continuing foci of research in northern Alaska. Results of an examination of the feeding ecology of tundra birds should also provide insight into two other problems which concern ecologists; namely, how different do diets of two or more species have to be to allow them to live sympatrically, and conversely, what are the consequences, ecologically and behaviorally, when two or more similar species exploit a common food source? This paper focuses on the diets and foodexploitation patterns of four widely sympatric sandpipers of the genus Calidris that breed regularly and abundantly near Barrow, Alaska. These are the red-backed (C. alpina), pectoral (C. melanotos), Baird's (C. bairdii) and semipalmated (C. pusillus) sandpipers. In addition, five other congeners are present occasionally in the Barrow area and can breed there: one is present almost every year, usually sparsely, but in occasional years commonly (C. fuscicollis); the other four are only sporadic or infrequent breeders, occurring in small numbers (canutus, alba, mauri and ferruginea). A sixth (ruficollis) also occurs sporadically and may yet be found to breed. This is the largest group of avian congeners that occurs near Barrow, but its members are not the only insectivores present. Other shorebirds, ducks, gulls, and a few passerines also breeding there take the same general kinds of foods as the sandpipers. Thus, the problems related to sympatry and use of a common food source extend beyond the group of species considered here. But the four common species of Calidris comprise a substantial part of the insectivore fauna in the Barrow area. Given these four variations on a basic theme of structure, physiology and behavior (the genus Calidris) that are regularly and abundantly present on the grass-sedge tundra near Barrow, we seek clues from differences between them as to factors permitting their coexistence. Our immediate objective is to describe diet and to examine degree of overlap.
191 citations
TL;DR: The dynamics of the organization of a community of six species of migrant predatory shorebirds was appraised by studying foraging behavior and habitat utilization under winter conditions in southern Florida and under summer conditions in the eastern Canadian Arctic.
Abstract: The dynamics of the organization of a community of six species of migrant predatory shorebirds (Least Sandpiper, Semipalmated Sandpiper, Dunlin, Short—billed Dowitcher, Lesser Yellowlegs, and Semipalmated Plover) was appraised by studying foraging behavior and habitat utilization under winter conditions in southern Florida and under summer conditions in the eastern Canadian Arctic. Eight foraging methods, defined primarily on the basis of how the bill is used and the pattern of locomotion, constitute the behavioral repertoire of the species. Each foraging method is correlated with a particular rate of locomotion (distance/time) and rate of feeding (pecking or probing/time). Feeding and locomotion rates seem independent of air temperature, number of conspecifics, and total number of shorebirds foraging nearby. Instead, the seasonal changes in these rates are probably related to food density. On the basis of these findings and of differences in rates of feeding and locomotion between species the most reason...
160 citations