The role of eddies in the diving behaviour of female southern elephant seals

As the Antarctic Circumpolar Current crosses the South-West Indian Ocean Ridge, it creates an extensive eddy field characterised by high sea level anomaly variability. We investigated the diving behaviour of female southern elephant seals from Marion Island during their post-moult migrations in relation to this eddy field in order to determine its role in the animals’ at-sea dispersal. Most seals dived within the region significantly more often than predicted by chance, and these dives were generally shallower and shorter than dives outside the eddy field. Mixed effects models estimated reductions of 44.33 ± 3.00 m (maximum depth) and 6.37 ± 0.10 min (dive duration) as a result of diving within the region, along with low between-seal variability (maximum depth: 5.5 % and dive duration: 8.4 %). U-shaped dives increased in frequency inside the eddy field, whereas W-shaped dives with multiple vertical movements decreased. Results suggest that Marion Island’s adult female elephant seals’ dives are characterised by lowered cost-of-transport when they encounter the eddy field during the start and end of their post-moult migrations. This might result from changes in buoyancy associated with varying body condition upon leaving and returning to the island. Our results do not suggest that the eddy field is a vital foraging ground for Marion Island’s southern elephant seals. However, because seals preferentially travel through this area and likely forage opportunistically while minimising transport costs, we hypothesise that climate-mediated changes in the nature or position of this region may alter the seals’ at-sea dispersal patterns.     

Optimal diving behaviour for foraging in relation to body size

Overall, large animals dive longer and deeper than small animals; however, after the difference in body size is taken into account, smaller divers often tend to make relatively longer dives. Neither physiological nor theoretical explanations have been provided for this paradox. This paper develops an optimal foraging diving model to demonstrate the effect of body size on diving behaviour, and discusses optimal diving behaviour in relation to body size. The general features of the results are: (1) smaller divers should rely more heavily on anaerobic respiration, (2) larger divers should not always make longer dives than smaller divers, and (3) an optimal body size exists for each diving depth. These results explain the relatively greater diving ability observed in smaller divers, and suggest that if the vertical distribution of prey in the water column is patchy, there is opportunity for a population of diving animals to occupy habitat niches related to body size.     

Assortative mating,sexual size dimorphism and sex determination in a seabird with plumage polymorphism

Intraspecific plumage polymorphism in seabirds is often attributed to advantages in foraging activities and escape from predators, but its role in sexual selection is not well understood. The Trindade petrel (Pterodroma arminjoniana) presents morphs varying from pale to whole dark, with no apparent sexual size dimorphism (SSD). We tested assortative mating in Trindade petrels based on plumage colours and body size. In addition, genders of Trindade petrels were identified molecularly aiming to test SSD based on morphometrics, which was also used to generate a discriminant function for sex assignment. Within-pair consistency in plumage colour (i.e. birds paired with mates of the same morph) was detected in 9 out of 10 pairs, but not in morphometric traits. Minimum bill depth and bill depth at unguis were traits significantly larger in males. The best model was adjusted with Bill depth at unguis, wing chord and body mass, with global discriminatory power of 78.4%. Our results suggest that plumage colours may be sexually selected in Trindade petrels, which brings evolutionary implications on the persistence of plumage polymorphism. Discriminatory power of the best discriminant function was similar to those found in other Procellariiformes and also among datasets obtained by distinct researchers, demonstrating its robustness.     

Targeting efforts in rescue programmes mitigating light-induced seabird mortality: First the fat,then the skinny

Oceanic conditions determine food availability to seabirds and affect seabird reproductive parameters, such as breeding success, chick growth, and survival rates. In seabirds, juvenile survival at sea is positively correlated with body condition at fledging. In addition, in several seabird species, especially petrels and shearwaters (Order Procellariiformes), fledglings are disoriented by artificial lights during their maiden flights from their nests to the sea, and many of them fall on the ground and are rescued by volunteers to mitigate light-induced mortality. We studied variations in body condition and body mass in Cory’s Shearwater (Calonectris borealis) fledglings on Faial Island (Azores), using data from rescue campaigns conducted over 15 consecutive years. We checked if body condition was related to oceanic conditions. Late fledglings were in poorer body condition than early ones. Significant inter-annual variations in fledging body condition were observed. These were not related to North Atlantic Oscillation fluctuations. However, annual mean fledgling body condition was positively correlated with sea surface temperatures measured in the autumn of the previous year in a northern feeding area used by adults throughout the breeding season. This study broadens our knowledge of the factors affecting fledgling body condition in Procellariiformes and provides advice to better manage the rescue campaigns. Optimal management of rescue campaigns is essential given the limited economic or human resources allocated to such an aim.     

Deep-diving of Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis>) during their marine feeding migrations

Data from seven data storage tags recovered from Atlantic salmon marked as smolts were analyzed for depth movements and patterns of deep diving during the marine migration. The salmon mostly stayed at the surface and showed diurnal activity especially from autumn until spring. During the first months at sea the salmon stayed at shallower depths (<100 m). The salmon took short deep dives (>100 m), that were rare or absent during the first summer at sea but increased in frequency and duration especially in late winter. The maximum depth of the dives varied from 419 to 1187 m. Most of dives were short, (<5 h) but could last up to 33 h. The duration of dives increased in late winter until spring and the overall depth and maximum depth per dive increased exponentially over time. The initiation of the dives was more common in evenings and at night, suggesting nocturnal diving. We hypothesized that deep diving is related to feeding of salmon as mesopelagic fish can be important food for salmon during winter.     

Interactive effects of body mass changes and species‐specific morphology on flight behavior of chick‐rearing Antarctic fulmarine petrels under diurnal wind patterns

For procellariiform seabirds, wind and morphology are crucial determinants of flight costs and flight speeds. During chick‐rearing, parental seabirds commute frequently to provision their chicks, and their body mass typically changes between outbound and return legs. In Antarctica, the characteristic diurnal katabatic winds, which blow stronger in the mornings, form a natural experimental setup to investigate flight behaviors of commuting seabirds in response to wind conditions. We GPS‐tracked three closely related species of sympatrically breeding Antarctic fulmarine petrels, which differ in wing loading and aspect ratio, and investigated their flight behavior in response to wind and changes in body mass. Such information is critical for understanding how species may respond to climate change. All three species reached higher ground speeds (i.e., the speed over ground) under stronger tailwinds, especially on return legs from foraging. Ground speeds decreased under stronger headwinds. Antarctic petrels (Thalassoica antarctica; intermediate body mass, highest wing loading, and aspect ratio) responded stronger to changes in wind speed and direction than cape petrels (Daption capense; lowest body mass, wing loading, and aspect ratio) or southern fulmars (Fulmarus glacialoides; highest body mass, intermediate wing loading, and aspect ratio). Birds did not adjust their flight direction in relation to wind direction nor the maximum distance from their nests when encountering headwinds on outbound commutes. However, birds appeared to adjust the timing of commutes to benefit from strong katabatic winds as tailwinds on outbound legs and avoid strong katabatic winds as headwinds on return legs. Despite these adaptations to the predictable diurnal wind conditions, birds frequently encountered unfavorably strong headwinds, possibly as a result of weather systems disrupting the katabatics. How the predicted decrease in Antarctic near‐coastal wind speeds over the remainder of the century will affect flight costs and breeding success and ultimately population trajectories remains to be seen.     

Diving behaviour of white-chinned petrels and its relevance for mitigating longline bycatch

The white-chinned petrel (Procellaria aequinoctialis) is the seabird species most commonly killed by Southern Hemisphere longline fisheries. Despite the importance of diving ability for mitigating longline bycatch, little is known of this species’ diving behaviour. We obtained data from temperature–depth recorders from nine white-chinned petrels breeding on Marion Island, southwestern Indian Ocean, during the late incubation and chick-rearing period. Maximum dive depth (16 m) was slightly deeper than the previous estimate (13 m), but varied considerably among individuals (range 2–16 m). Males dived deeper than females, and birds feeding chicks dived deeper than incubating birds, but dive rate did not differ between the sexes. Time of day had no significant effect on dive depth or rate. Our findings will help to improve the design and performance of mitigation measures aimed at reducing seabird bycatch in longline fisheries, such as the calculation of minimum line sink rates and optimum aerial coverage of bird-scaring lines.     

Takeoff flight performance and plumage wettability in Cassin’s Auklet Ptychoramphus aleuticus, Xantus’s Murrelet Synthliboramphus hypoleucus and Leach’s Storm-petrel Oceanodroma leucorhoa

Due to their marine habitats and distinctive foraging modes, seabirds face unique challenges with respect to flying that are negotiated differently by various species. One such challenge is taking off from the water with wet plumage. This study evaluated plumage wettability and takeoff performance in three seabird species: two wing-propelled divers with high wing loading, Cassin’s Auklet Ptychoramphus aleuticus and Xantus’s Murrelet Synthliboramphus hypoleucus; and Leach’s Storm-petrel Oceanodroma leucorhoa, a surface feeder with low wing loading. The plumages of the diving birds held less water than that of O. leucorhoa (~6.7% of body mass vs 9.5%). This difference is explained by O. leucorhoa’s surface to volume ratio being larger than that of the alcids. Furthermore, the alcids have afterfeathers larger than those of O. leucorhoa, which promotes a better insulation during diving. Examination of takeoff performance both before and after experimentally submerging the birds indicated that wingbeat frequency, speed and mass-specific power (peak and mean), and energy per wingbeat decreased in all species when plumage was experimentally wetted, whereas mean acceleration increased. O. leucorhoa was more strongly affected by wet plumage than the alcids, with a 32% of reduction in mass-specific energy per wingbeat compared to ≤25% in the alcids. Takeoff angle was reduced in alcids, but not significantly so in O. leucorhoa. Our results offer insights into the takeoff mechanics problems of wet seabirds given their differences in life history and morphology.     

Diving behavior and movements of juvenile hawksbill turtles Eretmochelys imbricata on a Caribbean coral reef

As historically abundant spongivores, hawksbill turtles Eretmochelys imbricata likely played a key ecological role on coral reefs. However, coral reefs are now experiencing global declines and many hawksbill populations are critically reduced. For endangered species, tracking movement has been recognized as fundamental to management. Since movements in marine vertebrates encompass three dimensions, evaluation of diving behavior and range is required to characterize marine turtle habitat. In this study, habitat use of hawksbill turtles on a Caribbean coral reef was elucidated by quantifying diel depth utilization and movements in relation to the boundaries of marine protected areas. Time depth recorders (TDRs) and ultrasonic tags were deployed on 21 Cayman Islands hawksbills, ranging in size from 26.4 to 58.4 cm straight carapace length. Study animals displayed pronounced diel patterns of diurnal activity and nocturnal resting, where diurnal dives were significantly shorter, deeper, and more active. Mean diurnal dive depth (±SD) was 8 ± 5 m, range 2–20 m, mean nocturnal dive depth was 5 ± 5 m, range 1–14 m, and maximum diurnal dive depth was 43 ± 27 m, range 7–91 m. Larger individuals performed significantly longer dives. Body mass was significantly correlated with mean dive depth for nocturnal but not diurnal dives. However, maximum diurnal dive depth was significantly correlated with body mass, suggesting partitioning of vertical habitat by size. Thus, variable dive capacity may reduce intraspecific competition and provide resistance to degradation in shallow habitats. Larger hawksbills may also represent important predators on deep reefs, creating a broad ecological footprint over a range of depths. Communicated by Biology Editor Dr Mark McCormick     

Size and experience matter: diving behaviour of juvenile New Zealand sea lions (Phocarctos hookeri)

The diving ability of juvenile animals is constrained by their physiology, morphology and lack of experience, compared to adults. We studied the influences of age and mass on the diving behaviour of juvenile (2–3-year-old females, n = 12; 3–5-year-old males, n = 7) New Zealand (NZ) sea lions (Phocarctos hookeri) using time–depth recorders (TDRs) from 2008 to 2010 in the NZ subantarctic Auckland Islands. Diving ability (e.g. dive depth, duration and bottom time per dive) improved with age and mass. However, the percentage of each dive spent at the bottom, along with percentage time at sea spent diving, was comparable between younger and lighter juveniles and older and heavier juveniles. These suggest that younger and older juveniles expend similar foraging effort in terms of the amount of time spent underwater. Only, 5-year-old male juveniles dove to adult female depths and durations and had the highest foraging efficiency at depths >250 m. It appears that juvenile NZ sea lions attain adult female diving ability at around 5 years of age (at least in males), but prior to this, their performance is limited. Overall, the restricted diving capabilities of juvenile NZ sea lions may limit their available foraging habitat and ability to acquire food at deeper depths. The lower diving ability of juvenile NZ sea lions compared to adults, along with juvenile-specific constraints, should be taken into consideration for the effective management of this declining, nationally critical species.     

Stable isotope evidence of diverse species-specific and individual wintering strategies in seabirds

Although there is increasing evidence that climatic variations during the non-breeding season shape population dynamics of seabirds, most aspects of their winter distribution and ecology remain essentially unknown. We used stable isotope signatures in feathers to infer and compare the moulting (wintering) habitat of subantarctic petrels breeding at two distant localities (South Georgia and Kerguelen). Petrels showed species-specific wintering habitat preferences, with a similar pattern of latitudinal segregation for all but one taxon. At both localities, delta13C values indicated that blue petrels (Halobaena caerulea) moult in Antarctic waters, South Georgian diving petrels (Pelecanoides georgicus) in the vicinity of the archipelagos and/or in the Polar Frontal Zone and Antarctic prions (Pachyptila desolata) in warmer waters. In contrast, common diving petrels (Pelecanoides urinatrix) showed divergent strategies, with low and high intrapopulation variation at South Georgia and Kerguelen, respectively. Birds from Kerguelen dispersed over a much wider range of habitats, from coastal to oceanic waters and from Antarctica to the subtropics, whereas those from South Georgia wintered mainly in waters around the archipelago. This study is the first to show such striking between-population heterogeneity in individual wintering strategies, which could have important implications for likely demographic responses to environmental perturbation.     

The physiological and behavioural development of diving in Australian fur seal (<Emphasis Type="Italic">Arctocephalus pusillus doriferus</Emphasis>) pups

The physiological and behavioural development of diving was examined in Australian fur seal (Arctocephalus pusillus doriferus) pups to assess whether animals at weaning are capable of exploiting the same resources as adult females. Haematocrit, haemoglobin and myoglobin contents all increased throughout pup development though total body oxygen stores reached only 71% of adult female levels just prior to weaning. Oxygen storage components, however, did not develop at the same pace. Whereas blood oxygen stores had reached adult female levels by 9 months of age, muscle oxygen stores were slower to develop, reaching only 23% of adult levels by this age. Increases in diving behaviour corresponded to the physiological changes observed. Pups spent little time (<8%) in the water prior to moulting (age 1–2 months) whereas following the moult, they spent >27% of time in the water and made mid-water dives (maximum depth 35.7 ± 2.9 m) with durations of 0.35 ± 0.03 min. By 9 months (just prior to weaning), 30.5 ± 9.3% of all dives performed were U-shaped benthic dives (maximum depth 65.0 ± 6.0 m) with mean durations of 0.87 ± 0.25 min, significantly shorter than those of adult females. These results suggest that while Australian fur seal pups approaching the age of weaning are able to reach similar depths as adult females, they do not have the physiological capacity to remain at these depths for sufficient durations to exploit them to the same efficiency.     

Flight behaviour of seabirds in relation to wind direction and wing morphology

We studied flight direction relative to wind direction (hereafter referred to as "flight direction"), the relation between wing morphology and flight behaviour and interspecies relationships in flight behaviour among all major seabird taxa. We calculated wing loading and aspect ratios for 98 species from 1029 specimens. Species were sorted into 13 groups on the basis of similarity in patterns of flight direction. The primary flight direction of Pelecaniformes and Charadriiformes was into and across headwinds. The most common flight direction of Procellariiformes was across wind. Seabirds avoided flying with tailwinds. Wing loading and aspect ratios were positively correlated in Procellariiformes, Pelecaniformes and alcids but negatively correlated in larids. In Procellariiformes, incidence of headwind flight and that of tailwind flight were significantly correlated with wing loading and aspect ratio; species with higher wing loading and aspect ratios flew more often into headwinds and less often with tailwinds. In contrast, the proportion of Pelecaniformes and Charadriiformes flying with tailwinds increased significantly with increased wing loading. Our results demonstrate a close link in seabirds between flight behaviour, wing morphology and natural history patterns in terms of distribution, colony location, dispersal and foraging behaviour.     

Sex differences in the diving behaviour of a size-dimorphic capital breeder: the grey seal

Both body size dimorphism and sex differences in the relative costs and benefits associated with acquiring energy for reproduction have been advanced to explain the evolution of sex differences in foraging behaviour. We examined the extent to which these factors influenced sex differences in the diving behaviour of a size-dimorphic, capital breeder, the grey seal, Halichoerus grypus. Using time-depth data loggers, we examined the diving behaviour of 46 male and 49 female grey seals for 7 months before parturition and mating. Males and females showed significantly different seasonal patterns in the characteristics of individual dives and dive effort. Compared with males, females showed significantly higher levels of dive effort immediately following moult and in the 3 months before parturition. Females also had longer dives (5.5 versus 4.9 min) and spent more time at depth (3.4 versus 2.7 min), whereas males dived deeper (57 versus 49 m). Males dived consistently throughout the day, whereas females showed strong diurnal patterns in dive depth, duration and frequency. The diving behaviour and rates of mass gain by females suggested a pattern of foraging consistent with early accumulation of body energy to support pregnancy and the subsequent lactation period during which females fast. Males, on the other hand, showed diving behaviour and rates of mass gain consistent with a more gradual accumulation of energy stores. Our results suggest that sex differences in the seasonal patterns of diving behaviour reflect sex differences in the costs and benefits of stored energy for reproduction rather than the influence of body size dimorphism alone.     

How slow breeding can be selected in seabirds: testing Lack's hypothesis

The historical debate of the 1960s between group and individual selection hinged on how the slow breeding of seabirds could be explained. While this debate was settled by the ascendance of individual selection, championed by David Lack, explanations for slow breeding in seabirds remain to be tested. We examined the slowest breeding of these birds, the albatrosses and petrels (order Procellariiformes), using analyses that statistically controlled for variations in body size and phylogeny. Incubation and fledging periods appeared strongly correlated, but this turned out to be largely explained by phylogeny. Nonetheless, developmental and reproductive rates were associated with the distance to the foraging range, as predicted under the hypothesis of ecological constraints on breeding pairs, and these results were independent of body size and phylogeny. Slower breeding in these seabirds appeared associated with the rigors of farther pelagic feeding, as Lack originally hypothesized.     

Impact of externally attached loggers on the diving behaviour of the king penguin

The impact of relatively small externally attached time series recorders on some foraging parameters of seabirds was investigated during the austral summer of 1995 by monitoring the diving behaviour of 10 free-ranging king penguins (Aptenodytes patagonicus) over one foraging trip. Time-depth recorders were implanted in the abdominal cavities of the birds, and half of the animals also had dummy loggers attached on their backs. Although most of the diving behaviour was not significantly affected by the external loggers (P>0.05), the birds with externally attached loggers performed almost twice as many shallow dives, between 0 and 10 m depth, as the birds without external loggers. These shallow dives interrupted more frequently the deep-diving sequences in the case of birds with external loggers (percentage of deep dives followed by deep dives: 46% for birds with implants only vs. 26% for birds with an external attachment). Finally, the distribution pattern of the postdive durations plotted against the hour of the day was more heterogeneous for the birds with an external package. In addition, these penguins had extended surfacing times between two deep dives compared to birds without external attachments (P<0.0001). These results suggest the existence of an extra energy cost induced by externally attached loggers.     

High diving metabolism results in a short aerobic dive limit for Steller sea lions (Eumetopias jubatus)

The diving capacity of marine mammals is typically defined by the aerobic dive limit (ADL) which, in lieu of direct measurements, can be calculated (cADL) from total body oxygen stores (TBO) and diving metabolic rate (DMR). To estimate cADL, we measured blood oxygen stores, and combined this with diving oxygen consumption rates (VO₂) recorded from 4 trained Steller sea lions diving in the open ocean to depths of 10 or 40 m. We also examined the effect of diving exercise on O₂ stores by comparing blood O₂ stores of our diving animals to non-diving individuals at an aquarium. Mass-specific blood volume of the non-diving individuals was higher in the winter than in summer, but there was no overall difference in blood O₂ stores between the diving and non-diving groups. Estimated TBO (35.9 ml O₂ kg^?1) was slightly lower than previously reported for Steller sea lions and other Otariids. Calculated ADL was 3.0 min (based on an average DMR of 2.24 L O₂ min^?1) and was significantly shorter than the average 4.4 min dives our study animals performed when making single long dives—but was similar to the times recorded during diving bouts (a series of 4 dives followed by a recovery period on the surface), as well as the dive times of wild animals. Our study is the first to estimate cADL based on direct measures of VO₂ and blood oxygen stores for an Otariid and indicates they have a much shorter ADL than previously thought.     

Low population density and biology of an island population of house mice <Emphasis Type="Italic">Mus musculus</Emphasis> on South Georgia

South Georgia has been the southernmost location where populations of invasive house mice Mus musculus are found. The distribution of mice was investigated at Cape Rosa and the Nuñez Peninsula, the two areas of South Georgia where the species is known to occur. Live-trapping and kill-trapping took place during March 2012, at the end of the austral summer, with traps in four grids (3.2–4.0 ha in area) and on 34 trap lines distributed across a range of habitats from the shoreline to 250 m above sea level. Mice were scarce, with just 68 captures in about 1750 trap nights. Mouse densities in tussock habitat were estimated at 2.1–2.8 mice/ha, with higher densities of 5.3–6.4 mice/ha along the coastline. Mice were found in all habitats apart from higher-altitude fellfield, but were relatively less abundant in tussock habitat with large numbers of seals. Mice were breeding at both sites with 58 % of mature females pregnant or lactating. Litter size (7.1 ± 2.3 embryos) and adult body mass (21.4 ± 4.6 g) were typical of most other island mice populations. Population densities of mice on South Georgia are two orders of magnitude lower than mouse densities measured at other sub-Antarctic islands. The very low population density and its restricted distribution, with most captures close to the shore, and the presence of large numbers of burrowing petrels and South Georgia pipits Anthus antarcticus at both sites, suggest that mice have a relatively limited impact on South Georgia’s vertebrate biodiversity.     

Effects of air and water temperatures on resting metabolism of auklets and other diving birds

For small aquatic endotherms, heat loss while floating on water can be a dominant energy cost, and requires accurate estimation in energetics models for different species. We measured resting metabolic rate (RMR) in air and on water for a small diving bird, the Cassin's auklet (Ptychoramphus aleuticus), and compared these results to published data for other diving birds of diverse taxa and sizes. For 8 Cassin's auklets (~165 g), the lower critical temperature was higher on water (21 °C) than in air (16 °C). Lowest values of RMR (W kg?1) averaged 19% higher on water (12.14 ± 3.14 SD) than in air (10.22 ± 1.43). At lower temperatures, RMR averaged 25% higher on water than in air, increasing with similar slope. RMR was higher on water than in air for alcids, cormorants, and small penguins but not for diving ducks, which appear exceptionally resistant to heat loss in water. Changes in RMR (W) with body mass either in air or on water were mostly linear over the 5- to 20-fold body mass ranges of alcids, diving ducks, and penguins, while cormorants showed no relationship of RMR with mass. The often large energetic effects of time spent floating on water can differ substantially among major taxa of diving birds, so that relevant estimates are critical to understanding their patterns of daily energy use.     

Phylogenetic affinities and taxonomy of the Oligocene Diomedeoididae,and the basal divergences amongst extant procellariiform birds

The Palaeogene Diomedeoididae are amongst the earliest representatives of procellariiform birds (albatrosses, tubenoses, and allies). Although several fossils of these birds have been reported in the past, many details of their osteology remained unknown. Here we describe a comprehensive collection of diomedeoidid fossils from the Rupelian stratotype in Belgium, which was found more than 100 years ago. The material includes all major limb elements as well as other cranial and postcranial bones, and allows the recognition of previously unknown features of phylogenetic significance. Based on these new osteological data, diomedeoidids were for the first time subjected to a phylogenetic analysis, which resulted in a position outside a clade including Hydrobatidae (northern storm‐petrels), Pelecanoididae (diving‐petrels), and Procellariidae (fulmars, petrels, shearwaters, and allies), either as the sister taxon of Diomedeidae (albatrosses) or as that of all crown group Procellariiformes. The latter placement is better supported by the osteological evidence, and diomedeoidids lack several apomorphies of crown group Procellariiformes. Previously unrecognized derived features are reported that support a monophyletic Hydrobatidae, thus contradicting recent proposals that Oceanitinae (southern storm‐petrels) are the earliest diverging crown group Procellariiformes. The new fossils also have a bearing on the convoluted taxonomy of diomedeoidids, and Diomedeoides Fischer, 1985 is synonymized with Rupelornis van Beneden, 1871. Diomedeoides lipsiensis (Fischer, 1983) is synonymous with Rupelornis definitus (van Beneden, 1871), a species that exhibits a large size range. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 854–875.