Diving at the shallow end: Green turtle behaviour in near-shore foraging habitat

Green turtles Chelonia mydas of immature and adult size (n = 19, curved carapace length 49 to 118 cm) were equipped with time-depth recorders for short periods (≤ 7 d) to investigate diel and seasonal variation in diving behaviour. Research sessions were distributed over 2 years to cover seasonal variation in sea temperature from 14 °C to 30 °C. Diurnal dives were shallower and shorter than nocturnal dives, with diel patterns also evident in dawn and dusk peaks in occupation of depths within 1 m of the surface, elevated diurnal occupation of depths 1 to 2 m below the surface and elevated nocturnal occupation of depths > 2 m. Dive duration increased as sea temperature decreased, showing strong negative correlation by day and by night. Study turtles made resting dives that were 3 to 4 times longer in median duration, and six times longer in maximum duration, at cool temperatures than they were at warm temperatures, but there was no evidence of winter diapause or location shift to avoid cold water. The large majority of turtles spent 89 to 100% of their time at depths ≤ 5 m below the surface, three individuals did not exceed 3 m and the maximum depth recorded by any turtle was 7.9 m, although deeper water was available. Furthermore, the dive data indicated that study turtles collectively spent more than 80% of their time at charted (low tide) depths of 3 m or less, indicating that they consistently used the shallow margins of the bay where human activities tend to be concentrated, thereby potentially increasing their exposure to anthropogenic threats.     

Body mass and locomotor habits of the smallest darter,Anhinga minuta (Aves,Anhingidae)

During the Neogene of South America, Anhingidae was represented by several species, mainly with greater sizes than the extant members. In the present contribution, body mass and locomotor habits of Anhinga minuta, the smallest known darter, were inferred. Body mass was estimated using two methods, one with measures of a tibiotarsus (the holotype) and the other, with measurements of a humerus; locomotor habits were inferred through muscular reconstructions and wing parameters (wing span, wing area and wing loading). Estimates of wing span and wing area were based on the length of humerus, assuming a condition of isometry with respect to Anhinga anhinga; wing loading was obtained through a relation formula between wing area and body mass. The results obtained indicate a body mass of about 729 g, a wing span of 0.958 m, a wing area of 0.117 m² and a corresponding wing loading of 61 N/m². These values and also the proximal insertion of the musculus pectoralis are consistent with those of a soaring bird but with more frequent flapping than extant anhingids. Furthermore, the inferred musculature for tibiotarsus indicates abilities for swimming, climbing and moving through the vegetation as in extant representatives.     

Sorting out the Snakebirds: The species status,phylogeny, and biogeography of the Darters (Aves: Anhingidae)

Although the avian family Anhingidae is unequivocally monophyletic, the number and relationships of the component species within the single genus (Anhinga) have long remained unclear. Here, we use extensive mitochondrial and nuclear DNA sequence data (8,878 bp) to show that four species should be recognized. Our fully resolved and well‐supported tree shows that the American Anhinga (Anhinga anhinga) is sister to the three Old World species, with the Oriental (A. melanogaster) and African (A. rufa) Darters sister within the Old World clade, which also includes the Australian Darter (A. novaehollandiae). We estimate that the divergence between the New World and Old World branches occurred 19–22 mya, with the Australian Darter separating from its Old World congeners 14–16 mya and the Oriental and African species splitting ~10 mya. The genus is yet another example of osteological conservatism in the Suliformes, which is comparable to that shown by the cormorants and shags. Nevertheless, the relationships we infer are congruent with recent plumage studies and are biogeographically plausible. We suggest that further investigation of the variation within the African and Australian Darters would be of interest.     

The vaterite cover on the eggs of Anhinga anhinga and its effect on gas conductance (Aves: Anhingidae)

The nature of the chalky cover of Anhinga eggshells and its effect on gas conductance were studied. The cover consisted of microscopic spheres of nearly pure CaCO₃ in the form of vaterite. The pore canals were unbranched with an inorganic cap (Board's type 3(a) (ii)). The cover acted as a resistance in series with the underlying calcitic shell and accounted for approximately 6% of the total conductance.     

Diving behaviour in relation to water temperature in the southern elephant seal: foraging implications

Summary A time-depth-temperature recorder provided a continuous record of diving by a female southern elephant seal in relation to water temperature for 27 days (1939 dives) after completion of moult. Mean maximum dive depth was 391±2.6 m and the overall maximum was 775 m. Dives lasted on average 17.5±0.09 min. Most dives showed a rapid descent to the discontinuity between the cold surface water and warmer deep water. Consequently the seal spent 57% of its time while diving at a depth of 200–400 m when it may have been foraging. This strongly suggests that the seal was exploiting a food source at the discontinuity between vertically stratified water masses. The water temperature data also indicated that the seal was diving in waters south of the Antarctic Polar Front and at some distance from the northern edge of the pack ice. The seal spent 88% of its time under water. Normal surface intervals between dives lasted an average of 2.1 ± 0.1 min whereas 16 extended surface intervals (>10 min duration) lasted 32.7±4.6 min. Dives were deeper during the day than at night and all but one extended surface interval occurred at night. The pattern of dives was similar to records from northern elephant seals but this is the first study to show how diving behaviour relates to water temperature.     

Diving pattern and performance in relation to foraging ecology in the gentoo penguin, Pygoscelis papua

We present data on diving pattern and performance (dive depth, duration, frequency and organization during the foraging trip) in gentoo penguins Pygoscelis papua , obtained using time-depth recorders ( n = 9 birds, 99 foraging trips). These data are used to estimate various parameters of foraging activity, e.g. foraging range, prey capture rates, and are compared in relation to breeding chronology. Foraging trip duration was 6 h and 10 h, and trip frequency 1.0/day and 0.96/day, during the brooding and creche periods, respectively. Birds spent on average 52%of each foraging trip diving. Dive depth and duration were highly bimodal: shallow dives (< 21 m) averaged 4 m and 0.23 min, and deep dives (> 30 m) 80 m and 2.5 min, respectively. Birds spent on average 71%and 25%of total diving time in deep and shallow dives, respectively. For deep dives, dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals 2–3 times dive duration. We suggest that most shallow dives are searching/exploratory dives and most deep dives are feeding dives. Deep dives showed clear diel patterns averaging 40 m at dawn and dusk and 80–90 m at midday. Estimated foraging ranges were 2.3 km and 4.1 km during the brood and creche period, respectively. Foraging trip duration increased by 4 h between the brood and creche periods but total time spent in deep dives (i.e. time spent feeding) was the same (3 h). Of 99 foraging trips, 56%consisted of only one dive bout and 44%of 2–4 bouts delimited by extended surface intervals > 10 min. We suggest that this pattern of diving activity reflects variation in spatial distribution of prey rather than the effect of physiological constraints on diving ability.     

Comparative foraging ecology of Madagascar vangids (Vangidae)

The Vangidae, an endemic family in Madagascar, contains 14 species in 11 genera. The foraging behaviour of 13 species of vangids was investigated during the periods August-November 1989 and September-November 1990. These vangids are grouped into six bill types according to their bill shape, using the analogy of gripping tools: (1) forceps. (2) radio pliers, (3) strong pinchers, (4) pliers, (5) standard and (6) flat forceps types. We recognized seven foraging niches: (A) canopy-gleaning, (B) general, (C) ground-snatching, (D) trunk/ branch-probing, (E) leaf and twig/branch-gleaning/probing, (F) leaf and twig/branch-gleaning and (G) trunk-gleaning niches. Two or more coexisting species with the same foraging niche differed in their bill types. Those vangids that exploited similar resources segregated in their bill types, geographic ranges and/or foraging niches, presumably to avoid severe competition. Several vangid species partially occupied the ecological niche that would be filled by woodpeckers elsewhere.     

Prey selection and foraging constraints in common poorwills (Phalaenoptilus nuttallii: Aves: Caprimulgidae)

Predators that hunt by sight should be constrained by light levels. This problem should be especially acute in aerial predators such as common poorwills ( Phalaenoptilus nuttallii : Caprimulgidae), which capture small insects at night. The purpose of our study was to test the hypothesis that poorwills are constrained to catching larger insect taxa due to limitations of visual orientation under low light. We assessed diet by analysing poorwill faecal samples collected at nest and roost sites in the Cypress Hills of Saskatchewan where prey density is relatively low. Coleopterans (44% and 39% in 1991 and 1992, respectively) and lepidopterans (46% and 55%) dominated the diet, yet these two insect orders were rare in light-suction trap (22% lepidopterans and 1% coleopterans) and sticky trap samples (11% lepidopterans and 2% coleopterans). Based on measurements of femur length, all consumed coleopterans were > 5 mm long, even though 57% of those available were < 5 mm. Our results suggest that poorwills are constrained to taking prey above a certain size, but above this threshold, particular prey types and larger sizes may be selected. Selection for coleopterans may reflect the need to acquire polyunsaturated fat to facilitate the use of torpor.     

The choice of foraging methods of the Brown Dipper,Cinclus pallasii (Aves: Cinclidae)

The Brown Dipper,Cinclus pallasii, forages for large prey by diving deeply among submerged rocks, and for small prey in shallow water by wading and pecking on the bottom. Foraging by diving entailed a higher energy cost but resulted in taking larger prey than foraging by wading-and-pecking. Foraging by diving was seldom observed from May to October, but increased from December to April, when the dippers came into breeding condition and the proportion of large prey in the benthic fauna increased. During the breeding season, adult dippers fed themselves mainly by foraging by wading-and-pecking, whereas those feeding nestlings and fledglings foraged by diving. The foraging methods employed was determined by the individuals being fed and the abundance of the large prey. Foraging by diving may be advantageous for individuals provisioning their young because of the high gross intake rate, but may be less advantageous for the foragers themselves because of the high energy cost.     

The foraging ecology of sympatric marine fish in the genus Embiotoca (Embiotocidae): Importance of foraging behavior in prey size selection

Summary Two locally sympatric temperate marine reef fishes, Embiotoca jacksoni and E. lateralis (Embiotocidae), have high taxonomic similarity in diets. Subdivision of gammarid amphipods, their principal prey, was found. E. jacksoni took more tubicolous gammarid amphipods whereas E. lateralis consumed mostly free-living individuals. The species differed considerably with respect to between-individual variability in taxonomic compositions of their diets. Each E. jacksoni closely resembled other conspecifics in this regard while individual E. lateralis displayed very high between-fish variation. The principal interspecific difference in fish diets concerned the sizes of prey items taken. E. jacksoni ate small but very common items and the mean prey weight in their guts did not differ from random collections of available prey. E. lateralis concentrated on large, rarer sizes such that the average prey weight in their guts was much heavier than available or in the diet of E. jacksoni of the same length. Disparate foraging behaviors was a much better indicator of the relative differences in diets of these two fishes than was external fish morphology. E. jacksoni, which can winnow prey items from unwanted debris, was a relatively indiscriminant forager. E. lateralis did not winnow but actively searched for prey. This species was a much more discriminating forager, but displayed much variability in foraging behavior.     

Diving physiology and winter foraging behavior of a juvenile leopard seal (Hydrurga leptonyx)

Diving physiology and at-sea behavior of a juvenile leopard seal (Hydrurga leptonyx) were opportunistically measured in the Antarctic Peninsula during winter 2002. Total body oxygen stores were estimated from measures of hematocrit, hemoglobin, myoglobin, and total blood volume and were used to calculate an aerobic dive limit (ADL). Movement patterns and diving behavior were measured by equipping the seal with a Satellite Relay Data Logger that transmitted data from 8–31 August 2002. The seal remained in a focal area, in contrast to crabeater seals tracked simultaneously. The seal displayed short, shallow dives (mean 2.0±1.4 min, 44±48 m) and spent 99.9% of its time within the estimated ADL of 7.4 min. The shallow diving behavior contradicts previous diet research suggesting Antarctic krill (Euphausia superba) is the primary prey of leopard seals during the winter months as krill were found at deeper depths during this period. These measurements of diving and movement of a leopard seal provide valuable preliminary data necessary to develop future research on the at-sea behavior of an apex predator in the Antarctic ecosystem.     

Breeding ecology of the Basra Reed Warbler,Acrocephalus griseldis,in Iraq (Aves: Passeriformes: Acrocephalidae)

The population of the Basra Reed Warbler, Acrocephalus griseldis, which has a limited range confined to the marshlands of central and southern Iraq, has declined substantially due to massive degradation of its main breeding habitat in the Iraqi marshes during the 1980s and 1990s. The breeding habitat and breeding biology is described here. We discovered a remarkable extension of the breeding range in the extreme west of Iraq.     

Simulation of the evolution of root water foraging strategies in dry and shallow soils

Background and Aims

The dynamic structural development of plants can be seen as a strategy for exploiting the limited resources available within their environment, and we would expect that evolution would lead to efficient strategies that reduce costs while maximizing resource acquisition. In particular, perennial species endemic to habitats with shallow soils in seasonally dry environments have been shown to have a specialized root system morphology that may enhance access to water resources in the underlying rock. This study aimed to explore these hypotheses by applying evolutionary algorithms to a functional–structural root growth model.

Methods

A simulation model of a plant''s root system was developed, which represents the dynamics of water uptake and structural growth. The model is simple enough for evolutionary optimization to be computationally feasible, yet flexible enough to allow a range of structural development strategies to be explored. The model was combined with an evolutionary algorithm in order to investigate a case study habitat with a highly heterogeneous distribution of resources, both spatially and temporally – the situation of perennial plants occurring on shallow soils in seasonally dry environments. Evolution was simulated under two contrasting fitness criteria: (1) the ability to find wet cracks in underlying rock, and (2) maximizing above-ground biomass.

Key Results

The novel approach successfully resulted in the evolution of more efficient structural development strategies for both fitness criteria. Different rooting strategies evolved when different criteria were applied, and each evolved strategy made ecological sense in terms of the corresponding fitness criterion. Evolution selected for root system morphologies which matched those of real species from corresponding habitats.

Conclusions

Specialized root morphology with deeper rather than shallower lateral branching enhances access to water resources in underlying rock. More generally, the approach provides insights into both evolutionary processes and ecological costs and benefits of different plant growth strategies.     

Ecomorphology of eye shape and retinal topography in waterfowl (Aves: Anseriformes: Anatidae) with different foraging modes

Despite the large body of literature on ecomorphological adaptations to foraging in waterfowl, little attention has been paid to their sensory systems, especially vision. Here, we compare eye shape and retinal topography across 12 species representing 4 different foraging modes. Eye shape was significantly different among foraging modes, with diving and pursuit-diving species having relatively smaller corneal diameters compared to non-diving species. This may be associated with differences in ambient light intensity while foraging or an ability to tightly constrict the pupil in divers in order to facilitate underwater vision. Retinal topography was similar across all species, consisting of an oblique visual streak, a central area of peak cell density, and no discernible fovea. Because the bill faces downwards when the head is held in the normal posture in waterfowl, the visual streak will be held horizontally, allowing the horizon to be sampled with higher visual acuity. Estimates of spatial resolving power were similar among species with only the Canada goose having a higher spatial resolution. Overall, we found no evidence of ecomorphological adaptations to different foraging modes in the retinal ganglion cell layer in waterfowl. Rather, retinal topography in these birds seems to reflect the ‘openness’ of their habitats.     

The ecology of shallow water meiofauna in two New England estuaries

Summary The distribution and abundance of shallow subtidal meiofauna in four habitats in the Niantic and Pettaquamscutt estuaries in southeastern New England were studied from October 1964 through October 1965. Numbers of individuals ranged from 1,184 to 5,163/10 cm², and wet weights from 8.5 to 62.5 mg/10 cm². Nematodes were the dominant group, averaging 83% of the total numbers and 64% of the total biomass. Among the nematodes, epigrowth-feeding species were dominant at all four stations; in addition, deposit-feeding species were abundant at three stations where the amount of detritus was high relative to the fourth station. At these three stations ostracods and deposit-feeding polychaetes were also abundant.Nematodes showed marked seasonal changes i their species composition, with epigrowth-feeding species reaching maximum densities in spring and summer (coincident with observed increases in benthic microflora production), and deposit and omnivorous-feeding species in fall and winter (coincident with observed increases in organic detritus). Increases in the epigrowth feeders were responsible for significant increases in the total nematode populations in spring and summer.Ostracods were most abundant in late summer, fall and winter in association with the increases in detritus. Polychaetes, amphipods and lamellibranchs were most abundant in summer, the first-named in association with elevated water temperatures. Harpactacoid copepods were inconsistent in their seasonal distributions.Approximately 80% of the meiofauna occurred in the upper 3 cm of sediment. Copepods and ostracods were virtually limited to the upper 3 cm, while amphipods and lamellibranchs were limited to the upper 2 cm of sediment. Nematodes and polychaetes extended down to 5 cm (the lowest depth studied), although usually in significantly reduced numbers.Based on a thesis submitted in partial fulfillment of the requirements for the Ph.D. degree, University of Rhode Island, 1966. This study was supported in part by U.S. Bureau of Commercial Fisheries Grant No. 14-17-0007-189 (G). Some of the recent laboratory studies supported by National Science Foundation Grant No. GB 7796.     

Rapid allopatric speciation in logperch darters (Percidae: Percina)

Theory predicts that clades diversifying via sympatric speciation will exhibit high diversification rates. However, the expected rate of diversification in clades characterized by allopatric speciation is less clear. Previous studies have documented significantly higher speciation rates in freshwater fish clades diversifying via sympatric versus allopatric modes, leading to suggestions that the geographic pattern of speciation can be inferred solely from knowledge of the diversification rate. We tested this prediction using an example from darters, a clade of approximately 200 species of freshwater fishes endemic to eastern North America. A resolved phylogeny was generated using mitochondrial DNA gene sequences for logperches, a monophyletic group of darters composed of 10 recognized species. Divergence times among logperch species were estimated using a fossil calibrated molecular clock in centrarchid fishes, and diversification rates in logperches were estimated using several methods. Speciation events in logperches are recent, extending from 4.20 +/- 1.06 million years ago (mya) to 0.42 +/- 0.22 mya, with most speciation events occurring in the Pleistocene. Diversification rates are high in logperches, at some nodes exceeding rates reported for well-studied adaptive radiations such as Hawaiian silverswords. The geographic pattern of speciation in logperches was investigated by examining the relationship between degree of sympatry and the absolute age of the contrast, with the result that diversification in logperches appears allopatric. The very high diversification rate observed in the logperch phylogeny is more similar to freshwater fish clades thought to represent examples of sympatric speciation than to clades representing allopatric speciation. These results demonstrate that the geographic mode of speciation for a clade cannot be inferred from the diversification rate. The empirical observation of high diversification rates in logperches demonstrates that allopatric speciation can occur rapidly.