Evidence for fatal collisions and kleptoparasitism while plunge‐diving in Gannets

Plunge‐diving is a highly successful strategy for dealing with the challenges confronting birds feeding on pelagic prey. We tested for evidence of fatal injuries due to collision between conspecifics in plunge‐diving Australasian Gannets Morus serrator and Cape Gannets Morus capensis, respectively, by performing post‐mortem examinations of carcasses recovered from New Zealand waters and analysing video footage of Cape Gannet foraging events from South Africa. We found evidence of accidental collisions between Gannets and also observed a case of attempted kleptoparasitism, in which a diving Cape Gannet targeted a previously captured fish in the beak of a conspecific.     

Immature gannets follow adults in commuting flocks providing a potential mechanism for social learning

Group travel is a familiar phenomenon among birds but the causes of this mode of movement are often unclear. For example, flocking flight may reduce flight costs, enhance predator avoidance or increase foraging efficiency. In addition, naive individuals may also follow older, more experienced conspecifics as a learning strategy. However, younger birds may be slower than adults so biomechanical and social effects on flock structure may be difficult to separate. Gannets are wide‐ranging (100s–1000s km) colonial seabirds that often travel in V or echelon‐shaped flocks. Tracking suggests that breeding gannets use memory to return repeatedly to prey patches 10s–100s km wide but it is unclear how these are initially discovered. Public information gained at the colony or by following conspecifics has been hypothesised to play a role, especially during early life. Here, we address two hypotheses: 1) flocking reduces flight costs and 2) young gannets follow older ones in order to locate prey. To do so, we recorded flocks of northern gannets commuting to and from a large colony and passing locations offshore and used a biomechanical model to test for age differences in flight speeds. Consistent with the aerodynamic hypothesis, returning flocks were significantly larger than departing flocks, while, consistent with the information gathering hypothesis, immatures travelled in flocks more frequently than adults and these flocks were more likely to be led by adults than expected by chance. Immatures did not systematically occupy the last position in flocks and had similar theoretical airspeeds to adults, making it unlikely that they follow, rather than lead, for biomechanical reasons. We therefore conclude that while gannets are likely to travel in flocks in part to reduce flight costs, the positions of immatures in those flocks may result in a flow of information from adults to immatures, potentially leading to social learning.     

Visual accommodation and active pursuit of prey underwater in a plunge-diving bird: the Australasian gannet

Australasian gannets (Morus serrator), like many other seabird species, locate pelagic prey from the air and perform rapid plunge dives for their capture. Prey are captured underwater either in the momentum (M) phase of the dive while descending through the water column, or the wing flapping (WF) phase while moving, using the wings for propulsion. Detection of prey from the air is clearly visually guided, but it remains unknown whether plunge diving birds also use vision in the underwater phase of the dive. Here we address the question of whether gannets are capable of visually accommodating in the transition from aerial to aquatic vision, and analyse underwater video footage for evidence that gannets use vision in the aquatic phases of hunting. Photokeratometry and infrared video photorefraction revealed that, immediately upon submergence of the head, gannet eyes accommodate and overcome the loss of greater than 45 D (dioptres) of corneal refractive power which occurs in the transition between air and water. Analyses of underwater video showed the highest prey capture rates during WF phase when gannets actively pursue individual fish, a behaviour that very likely involves visual guidance, following the transition after the plunge dive's M phase. This is to our knowledge the first demonstration of the capacity for visual accommodation underwater in a plunge diving bird while capturing submerged prey detected from the air.     

When and how did Bos indicus introgress into Mongolian cattle?

The Mongolian cattle are one of the most widespread breeds with strictly Bos taurus morphological features in northern China. In our current study, we presented a diversity of mitochondrial DNA (mtDNA) D-loop region and Y chromosome SNP markers in 25 male and 8 female samples of Mongolian cattle from the Xinjiang Uygur autonomous region in Western China, and detected 21 B. taurus and four Bos indicus (zebu) mtDNA haplotypes. Among four B. indicus mtDNA haplotypes, two haplotypes belonged to I1 haplogroup and the remaining two haplotypes belonged to I2 haplogroup. In contrast, all 25 male Mongolian cattle samples revealed B. taurus Y chromosome haplotype and no B. indicus haplotypes were found. Historical and archeological records indicate that B. taurus was introduced to Xinjiang during the second millennium BC and B. indicus appeared in this region by the second century AD. The two types of cattle coexisted for many centuries in Xinjiang, as depicted in clay and wooden figurines unearthed in the Astana cemetery in Turfan (3rd–8th century AD). Multiple lines of evidence suggest that the earliest B. indicus introgression in the Mongolian cattle may have occurred during the 2nd–7th centuries AD through the Silk Road around the Xinjiang region. This conclusion differs from the previous hypothesis that zebu introgression to Mongolian cattle happened during the Mongol Empire era in the 13th century.     

A junk-food hypothesis for gannets feeding on fishery waste

Worldwide fisheries generate large volumes of fishery waste and it is often assumed that this additional food is beneficial to populations of marine top-predators. We challenge this concept via a detailed study of foraging Cape gannets Morus capensis and of their feeding environment in the Benguela upwelling zone. The natural prey of Cape gannets (pelagic fishes) is depleted and birds now feed extensively on fishery wastes. These are beneficial to non-breeding birds, which show reduced feeding effort and high survival. By contrast, breeding gannets double their diving effort in an attempt to provision their chicks predominantly with high-quality, live pelagic fishes. Owing to a scarcity of this resource, they fail and most chicks die. Our study supports the junk-food hypothesis for Cape gannets since it shows that non-breeding birds can survive when complementing their diet with fishery wastes, but that they struggle to reproduce if live prey is scarce. This is due to the negative impact of low-quality fishery wastes on the growth patterns of gannet chicks. Marine management policies should not assume that fishery waste is generally beneficial to scavenging seabirds and that an abundance of this artificial resource will automatically inflate their populations.     

Individual differences in searching behaviour and spatial foraging consistency in a central place marine predator

Consistent intra‐population variability in foraging behaviour is found among a wide range of taxa. Such foraging specialisations are common among marine vertebrates, yet it is not clear how individuals repeatedly locate prey or foraging sites at ocean‐wide scales. Using GPS and time‐depth loggers we studied the fine‐scale foraging behaviour of central‐place northern gannets Morus bassanus at two large colonies. First, we estimated the degree of consistency in individual foraging routes and sites across repeated trips. Second, we tested for individual differences in searching behaviour in response to environmental covariates using reaction norms, estimated from mixed effect models. Adult gannets tracked over multiple foraging trips showed repeatable between‐individual differences in terminal points and departure angles of foraging trips, but low repeatability in trip duration and trip length. Importantly, individual birds showed highly repeatable dive locations, with consistently different environmental conditions (such as copepod abundance), suggesting a high degree of foraging site specialisation. Gannets also showed between‐individual differences in searching behaviour along environmental gradients, such that individuals intensified searching under different conditions. Together these results suggest that widespread individual foraging consistency may represent specialisation and be linked with individual responses to environmental conditions. Such divergent searching behaviour could provide a mechanism by which consistent foraging behaviour arises and is maintained among animals that forage across large spatial scales.     

Differentiating between stopover and staging sites: functions of the southern and northern Yellow Sea for long‐distance migratory shorebirds

Evidence‐based protection of migratory birds at flyway levels requires a solid understanding of their use of ‘stopping sites’ during migration. To characterize the site use of northward‐migration great knots Calidris tenuirostris in China, we compared length of stay and fuel deposition during northward migration at areas in the south and the north of the Yellow Sea, a region critical for migrating shorebirds. Radio‐tracking showed that at the southern site great knots stayed for only short periods (2.3 ± 1.9 d, n = 40), and bird captures showed that they did not increase their mean body mass while there. In the north birds stayed for 1 month (31.0 ± 13.6 d, n = 22) and almost doubled their mean body mass. Fuel consumption models suggest that great knots departing from the northern Yellow Sea should be able to fly nonstop to the breeding grounds, whereas those from the south would require a refueling stop further north. These results indicate that the study sites in the northern and southern Yellow Sea serve different roles: the southern site acts as a temporary stopover area that enables birds with low fuel stores to make it to main staging areas further north, while the northern site serves as the critical staging site where birds refuel for the next leg of their migration. The rapid turnover rate in the southern Yellow Sea indicates that many more birds use that area than are indicated by peak counts. Differential use of the southern and northern sites indicates that both play crucial roles in the ability of great knots to migrate successfully.     

Diving behaviour of the Shy Albatross Diomedea cauta in Tasmania: initial findings and dive recorder assessment

The diving behaviour of the Shy Albatross Diomedea cauta was investigated using archival time-depth recorders (TDRs) and maximum depth gauges (MDGs). Data from birds carrying multiple devices and from diving simulations indicated that the degree of correspondence between TDRs and MDGs varied with the dive depth, duration and frequency, as well as with body placement. The MDGs were the most reliable when the diving depth was greater than 0.5 m, when the diving frequency was low and when gauges were placed on the birds' backs. The TDRs were used during late incubation and early chick rearing in 1994. Fifty-two dives (0.4 m) were recorded during 20 foraging trips of 15 individuals. The majority of dives were within the upper 3 m of the water column and lasted for less than 6 s. However, dives to 7.4 m and others lasting 19 s were recorded. The albatrosses dived between 07.00 h and 22.00 h, with peaks in their diving activity near midday and twilight. Mean diving depth varied throughout the day. with the deepest dives occurring between 10.00 h and 12.00 h. Two dive types were identified on the basis of the relationship between dive depth and descent rate. Plunge dives were short (5 s), and the birds reached a maximum depth of 2.9 m. Swimming dives were both longer and deeper. The characteristics of Shy Albatross plunge dives were similar to those of gannets Morus spp., which are known to be proficient plunge divers. Swimming dives suggest that Shy Albatrosses actively pursue prey underwater.     

Past, current, and future of the central European corridor for aquatic invasions in Belarus

We analyzed the role of the waterways of Belarus in the spread of aquatic exotic invertebrates through the central European invasion corridor. Present day Belarus became critically important when in the end of the 18th—beginning of the 19th century three interbasin canals connecting rivers from the Black and Baltic seas basins were constructed for international trade. These canals became important pathways facilitating the spread of aquatic alien species. For more than a hundred years, only Ponto-Caspian species colonized Belarus using ships and especially timber in rafts exported by Russia into Western Europe. In the second half of the 20th century, new vectors of spread appeared in Belarus, such as stocking of economically important invertebrates and accidental introductions. This paper is the first comprehensive review of aquatic exotic invertebrates in Belarus. Currently, 19 exotic aquatic invertebrates are known in Belarus, including 14 species of Ponto-Caspian origin. The rate of spread of aquatic invasive species in the second half of the 20th century increased 7-fold compared to the 19th—beginning of the 20th century. We found a significant positive correlation between the time since initial invasion and number of waterbodies colonized. We predict a further increase in the rate of colonization of Belarus by exotic invertebrates as well as an increase in the diversity of vectors of spread and donor areas of alien species, especially when the ongoing reconstruction of the interbasin canals will be completed and the hydrological connection between Black Sea and Baltic Sea basins will be reestablished after an interruption that has lasted for almost a century.     

Divergent diving behavior during short and long trips of a bimodal forager,the little auk Alle alle

The purpose of this study was to characterize for the first time seabird diving behavior during bimodal foraging. Little auks Alle alle, small zooplanktivorous Alcids of the High Arctic, have recently been shown to make foraging trips of short and long duration. Because short (ST) and long trips (LT) are thought to occur in different locations and serve different purposes (chick‐ and self‐feeding, respectively) we hypothesized that foraging differences would be apparent, both in terms of water temperature and diving characteristics. Using Time Depth Recorders (TDRs), we tested this hypothesis at three colonies along the Greenland Sea with contrasting oceanographic conditions. We found that diving behavior generally differed between ST and LT. However, the magnitude of the disparity in diving characteristics depended on local foraging conditions. At the study site where conditions were favorable, diving behavior differed only to a small degree between LT and ST. Together with a lack of difference in diving depth and ocean temperature, this indicates that these birds did not increase their foraging effort during ST nor did they travel long distances to seek out more profitable prey. In contrast, where local foraging conditions were poor, birds increased their diving effort substantially to collect a chick meal during ST as indicated by longer, more U‐shaped dives with slower ascent rates and shorter resting times (post‐dive intervals and extended surface pauses). In addition, large differences in diving depth and ocean temperature indicate that birds forage on different prey species and utilize different foraging areas during LT, which may be up to 200 km away from the colony. Continued warming and deteriorating near‐colony foraging conditions may have energetic consequences for little auks breeding in the eastern Greenland Sea.     

OBSERVATIONS OF THE MIGRATION OF RAPTORS AND OTHER LARGE SOARING BIRDS IN BULGARIA, 1975–1978

Observations are given, from the years 1975 to 1978, on the migrations of raptors and large soaring birds along the Bulgarian section of the Black Sea coast, with casual observations on passage in western and central Bulgaria. The winter status of pelicans, and of some raptors, is discussed.
The author's findings suggest that the main spring migration route follows the coast north from Burgas, rather than turning west there, as had been suggested.     

Radical changes in the Wadden Sea fauna and flora over the last 2,000 years

Humans have interacted with the Wadden Sea since its origin 7,500 years ago. However, exploitation, habitat alteration and pollution have strongly increased since the Middle Ages, affecting abundance and distribution of many marine mammals, birds, fish, invertebrates and plants. Large whales and some large birds disappeared more than 500 years ago. Most small whales, seals, birds, large fish and oysters were severely reduced by the late 19th and early 20th centuries, leading to the collapse of several traditional fisheries. In the 20th century, conservation efforts have enabled some breeding birds and seals to recover. But other species declined further due to continuing exploitation, habitat destruction, pollution and eutrophication. Moreover, complex three-dimensional habitats such as oyster banks, Sabellaria reefs and subtidal eelgrass beds have been lost completely. In contrast, several opportunistic species such as gulls, polychaetes, green algae and exotic invaders increased during the 20th century. Taken together, multiple human impacts have caused dramatic losses of large predators and habitat-building species in the Wadden Sea over the last 500 years. Although still of high natural value and global importance, the Wadden Sea is a fundamentally changed ecosystem. On the other hand, reduced hunting pressure, increased habitat protection and reduced river pollution have enabled the recent recovery of several species and an increase in environmental quality. These successes, together with a historical vision of what was once possible, should guide current and future conservation, restoration and management efforts towards a more sustainable interaction between man and the sea.     

The status and conservation of the Cape Gannet Morus capensis

The Cape Gannet Morus capensis is one of several seabird species endemic to the Benguela upwelling ecosystem (BUS) but whose population has recently decreased, leading to an unfavourable IUCN Red List assessment. Application of ‘JARA’ (‘Just Another Red-List Assessment,’ a Bayesian state-space tool used for IUCN Red List assessments) to updated information on the areas occupied by Cape Gannets and the nest densities of breeding birds at their six colonies, suggested that the species should be classified as Vulnerable. However, the rate of decrease of Cape Gannets in their most-recent generation exceeded that of the previous generation, primarily as a result of large decreases at Bird Island, Lambert’s Bay, and Malgas Island, off South Africa’s west coast (the western part of their range). Since the 1960s, there has been an ongoing redistribution of the species from northwest to southeast around southern Africa, and ～70% of the population now occurs on the south coast of South Africa, at Bird Island in Algoa Bay, on the eastern border of the BUS. Recruitment rather than adult survival may be limiting the present population; however, information on the seabird’s demographic parameters and mortality in fisheries is lacking for colonies in the northern part of the BUS. Presently, major threats to Cape Gannet include: substantially decreased availability of their preferred prey in the west; heavy mortalities of eggs, chicks and fledglings at and around colonies, inflicted by Cape Fur Seals Arctocephalus pusillus and other seabirds; substantial disturbance at colonies caused by Cape Fur Seals attacking adult gannets ashore; oiling; and disease.     

Cross sectional geometry of the forelimb skeleton and flight mode in pelecaniform birds

Avian wing elements have been shown to experience both dorsoventral bending and torsional loads during flapping flight. However, not all birds use continuous flapping as a primary flight strategy. The pelecaniforms exhibit extraordinary diversity in flight mode, utilizing flapping, flap‐gliding, and soaring. Here we (1) characterize the cross‐sectional geometry of the three main wing bone (humerus, ulna, carpometacarpus), (2) use elements of beam theory to estimate resistance to loading, and (3) examine patterns of variation in hypothesized loading resistance relative to flight and diving mode in 16 species of pelecaniform birds. Patterns emerge that are common to all species, as well as some characteristics that are flight‐ and diving‐mode specific. In all birds examined, the distal most wing segment (carpometacarpus) is the most elliptical (relatively high I_max/I_min) at mid‐shaft, suggesting a shape optimized to resist bending loads in a dorsoventral direction. As primary flight feathers attach at an oblique angle relative to the long axis of the carpometacarpus, they are likely responsible for inducing bending of this element during flight. Moreover, among flight modes examined the flapping group (cormorants) exhibits more elliptical humeri and carpometacarpi than other flight modes, perhaps pertaining to the higher frequency of bending loads in these elements. The soaring birds (pelicans and gannets) exhibit wing elements with near‐circular cross‐sections and higher polar moments of area than in the flap and flap‐gliding birds, suggesting shapes optimized to offer increased resistance to torsional loads. This analysis of cross‐sectional geometry has enhanced our interpretation of how the wing elements are being loaded and ultimately how they are being used during normal activities. J. Morphol., 2011. © 2011 Wiley‐Liss,Inc.     

An experimental assessment of the potential effects of human disturbance on Black Grouse Tetrao tetrix in the North Pennines,England

In the United Kingdom, Black Grouse Tetrao tetrix have declined in range and abundance during the 20th century. In England at present, birds are largely found only on the margins of managed grouse moors in the north, where more than 80% of birds are confined to the North Pennines Area of Outstanding Natural Beauty. The Black Grouse is one of a group of species potentially at risk from increased human recreational disturbance owing to their threatened status and their use of habitats to which a statutory right of human recreational access has recently been granted. To assess the likely impact of increased disturbance to Black Grouse, 77 were caught and radiotagged between 2002 and 2004, and each was randomly assigned to one of three experimental disturbance categories: no disturbance (low), fortnightly disturbance (moderate) or twice weekly disturbance (high). Birds that were disturbed more regularly flushed at greater distances, especially in spring and winter when birds exposed to high disturbance flushed at 32% greater distances than those in moderate disturbance treatments. There were no differences in fecundity (clutch size, hatching success, breeding success) or survival between disturbance treatments. Winter survival was 78% and summer survival 92%. There was no age‐related difference in survival. The disturbance regimes imposed had no discernible impact upon Black Grouse population dynamics. However, in the absence of appropriate data to indicate likely changes in patterns and levels of human recreation resulting from open access, we cannot be sure whether the levels we applied will be representative in the future. Should actual disturbance levels be higher than those we used in this study, we list visitor management options that may help reduce any conflict that arises.     

Individual seabirds show consistent foraging strategies in response to predictable fisheries discards

Current fishing extraction methods often generate huge quantities of dead or dying biomass that is returned to the sea in the form of discards. This practice produces a readily available clumped resource for many scavengers such as seabirds, but in the face of declining stocks and via policy change, the amount of discards produced is set to decline in the future. To understand how discards have influenced seabird foraging in the past and how birds may respond to future change requires studies examining consistent individual foraging choices. There is increasing evidence that populations may be made up of generalist or specialist foragers and this is key to the population's ability to adapt to change. Here we test for consistent individual foraging behaviour of northern gannets Morus bassanus in relation to fishing vessels and examine consequences of scavenging behaviour in terms of foraging effort and body condition. Using a combination of bird‐borne bio‐logging devices (GPS and Time Depth Recorders) with high resolution GPS data acquired through vessel monitoring systems on fishing boats, we examined the overlap between birds and fisheries. We found that during repeat foraging trips in the same breeding season, gannets regularly foraged at fishing boats but there were also clear among individual differences in the extent of fisheries overlap. Furthermore, we show for the first time that these differences represent consistent strategies – individual differences in scavenging were highly repeatable across multiple trips within a period of several weeks. However, despite this finding, we found no differences in foraging effort or body condition between scavengers and non‐scavengers. Moreover, scavenging strategy did not appear to influence diving behaviour or vary by sex. Scavenging on discards appears to be a strategy employed consistently by a subsection of the population and future work should examine whether these specialisations persist throughout and between years and what causes these individual differences, exploring possible demographic and fitness consequences in light of global changes to fish stocks and fisheries management.     

An experimental assessment of the potential effects of human disturbance on Black Grouse Tetrao tetrix in the North Pennines, England

In the United Kingdom, Black Grouse Tetrao tetrix have declined in range and abundance during the 20th century. In England at present, birds are largely found only on the margins of managed grouse moors in the north, where more than 80% of birds are confined to the North Pennines Area of Outstanding Natural Beauty. The Black Grouse is one of a group of species potentially at risk from increased human recreational disturbance owing to their threatened status and their use of habitats to which a statutory right of human recreational access has recently been granted. To assess the likely impact of increased disturbance to Black Grouse, 77 were caught and radiotagged between 2002 and 2004, and each was randomly assigned to one of three experimental disturbance categories: no disturbance (low), fortnightly disturbance (moderate) or twice weekly disturbance (high). Birds that were disturbed more regularly flushed at greater distances, especially in spring and winter when birds exposed to high disturbance flushed at 32% greater distances than those in moderate disturbance treatments. There were no differences in fecundity (clutch size, hatching success, breeding success) or survival between disturbance treatments. Winter survival was 78% and summer survival 92%. There was no age-related difference in survival. The disturbance regimes imposed had no discernible impact upon Black Grouse population dynamics. However, in the absence of appropriate data to indicate likely changes in patterns and levels of human recreation resulting from open access, we cannot be sure whether the levels we applied will be representative in the future. Should actual disturbance levels be higher than those we used in this study, we list visitor management options that may help reduce any conflict that arises.     

Late‐moulting Black‐necked Grebes Podiceps nigricollis show greater body mass in the face of failing food supply

From August to December, thousands of Black‐necked Grebes Podiceps nigricollis concentrate during the flightless moult period in salt ponds in the Odiel Marshes, southern Spain, where they feed on the brine shrimp Artemia parthenogenetica. We predicted that because Black‐necked Grebes moulted in a food‐rich, predator‐free environment, there would be no net loss of body mass caused by the use of fat stored to meet energy needs during remigial feather replacement (as is the case for some other diving waterbirds). However, because the food resource disappears in winter, we predicted that grebes moulting later in the season would put on more body mass prior to moult because of the increasing risk of an Artemia population crash before the moult period is completed. Body mass determinations of thousands of birds captured during 2000–2010 showed that grebes in active wing‐moult showed greater mass with date of capture. Early‐moulting grebes were significantly lighter at all stages than late‐moulting birds. Grebes captured with new feathers post‐moult were significantly lighter than those in moult. This is the first study to support the hypothesis that individual waterbirds adopt different strategies in body mass accumulation according to timing of moult: early‐season grebes were able to acquire an excess of energy over expenditure and accumulate fat stores while moulting. Delayed moulters acquired greater fat stores in advance of moult to contribute to energy expenditure for feather replacement and retained extra stores later, most likely as a bet hedge against the increasing probability of failing food supply and higher thermoregulatory demands late in the season. An alternative hypothesis, that mass change is affected by a trophically transmitted cestode using brine shrimps as an intermediate host and Black‐necked Grebes as final host, was not supported by the data.