Morus Serrator Research Articles

Pursuit plunging by northern gannets (Sula bassana) feeding on capelin (Mallotus villosus).

Northern gannets (Sula bassana) are considered to obtain prey usually by rapid, vertical, shallow plunge dives. In order to test this contention and investigate underwater foraging behaviour, we attached two types of data-logging systems to 11 parental northern gannets at Funk Island in the North-Wiest Atlantic. We documented, for the first time to the authors' knowledge, gannets performing long, flat-bottomed, U-shaped dives that involved underwater wing propulsion as well as rapid, shallow, V-shaped dives. The median and maximum dive depths and durations were 4.6 and 22.0 m and 8 and 38 s, respectively. Short, shallow dives were usually V-shaped and dives deeper than 8 m and longer than 10 s were usually U-shaped, including a period at constant depth (varying between 4 and 28s with median 8s). Diving occurred throughout the daylight period and deepest dives were performed during late morning. On the basis of motion sensors in the loggers and food collections from telemetered birds, we concluded that extended, deep dives were directed at deep schools of capelin, a small pelagic fish, and we hypothesized that V-shaped dives were aimed at larger, pelagic fishes and squids. Furthermore, these V-shaped dives allowed the birds to surprise their pelagic prey and this may be critical because the maximum swimming speeds of the prey species may exceed the maximum dive speeds of the birds.

Reproductive Parameters, Chick Growth and Adult ‘Age’ in Australasian Gannets Morus serrator Breeding in Port Phillip Bay, Victoria, in 1994–95

SummaryReproductive parameters of Australasian Gannets Morus serrator breeding at Pope's Eye in Port Phillip Bay, Victoria, Australia were examined in the 1994–95 breeding period. Contents of individual nests were determined during routine visits, and eggs and chicks measured. Nests and breeding birds were assigned to groups based on position and adults of known age (previously banded as chicks) as indicators. A severe storm in November 1994 removed most nests and resulted in extensive re-laying, particularly by older (centrally nesting) birds. The ability to re-lay and successfully raise young suggested that food (preferentially Pilchards Sardinops sagax, although gannets take a wide range of fish at this location) was not limiting, being abundant even towards later stages of the breeding cycle. ‘Older’ adults formed more central nests, laid earlier, and replaced more lost eggs than younger birds. Chicks of older adults were produced earlier and were heavier at comparable ages than those of younger birds. Age influences some reproductive parameters, and hence lifetime reproductive success, in this species as it does in other seabirds.

Changes in the diet of the Australasian gannet (Morus serrator) in response to the 1998 mortality of pilchards (Sardinops sagax)

The diet of Australasian gannets (Morus serrator) breeding in Port Phillip Bay was investigated before and after a mass mortality of pilchards (Sardinops sagax) in southern Australian waters in 1998. Gannets usually feed on inshore pelagic schooling fish, such as pilchards and barracouta (Thyrsites atun), and to a lesser extent on other species. Pilchards represented ~60% of the gannet diet examined before the spread of pilchard deaths into Victorian waters, but this component declined to 5% following the mortality event. This reduction was compensated by a substantial increase in the amount of barracouta taken, supporting the view that the gannet is a flexible forager. However, the 1998 mortality of pilchards is likely to have wider implications since pilchards are an important prey for other piscivorous fish, seabirds and marine mammals.

Lipid reserves, fasting capability and the evolution of nestling obesity in procellariiform seabirds

Several alternative explanations have been proposed to account for the evolution of nestling obesity in a variety of avian groups. These predict quite different patterns of fat accumulation, storage and use by chicks of different ages. Yet surprisingly few studies have measured changes in body composition during chick development. We tested the applicability of these hypotheses for fulmars, Fulmarus glacialis , by direct measurement of changes in water, lipid and lean dry mass in growing chicks. Lipid and lean dry mass increased until ca. 70% of the way through chick rearing, but then levelled off. Total body water also increased until the same stage, but gradually declined thereafter, and it was this change rather than fat metabolism that resulted in mass recession. The observed pattern of a continued increase in stored lipid, and most importantly, its maintenance all the way through the mass–recession phase until chicks reach fledging, is incompatible with many of the proposed hypotheses. We suggest that the most likely ultimate explanation for large fat deposits is to fuel chicks during the initial critical period away from the nest site while they learn to forage

Recent Changes in the Status of Australasian Gannets Morus serrator in Victoria

Recent Changes in the Status of Australasian Gannets Morus serrator in Victoria

Phylogeny and Evolution of the Sulidae (Aves: Pelecaniformes): A Test of Alternative Modes of Speciation

Although the allopatric model of speciation is widely accepted, it does not provide a satisfactory explanation for many evolutionary phenomena. Several alternative models exist, but they remain largely untested for vertebrate animals. In the present paper, a molecular phylogeny was used to test competing models of speciation in a seabird family, the Sulidae. A segment including 807 base pairs of the mitochondrial cytochromebgene was sequenced from all extant sulid species, and phylogenetic methods were used to test model-specific predictions regarding tree topologies, distributions of sister taxa, timing of vicariant events, and comparative biology. Both the neighbor-joining and parsimony analyses placed sequences of gannets (Morusspp.) and boobies of the genusSulain separate, monophyletic lineages. Sequences of Cape (M. capensis) and Australasian (M. serrator) gannets clustered together, and the sequence of Abbott's booby (Papasula abbotti) was basal to those of the gannets. Sequences of blue-footed (S. nebouxii) and Peruvian (S. variegata) boobies were sisters and formed a monophyletic group with the masked booby (S. dactylatra). The red-footed booby (S. sula) sequence was the most divergent of theSulaboobies. All relationships received strong support from standard-error tests and bootstrap analysis. Substitution rates were similar to those suggested for mammals and suggested that most lineages arose within the last 3 million years. Lineage divergence events for which the mode of speciation could be deduced did not fit the predictions of either allopatric or sympatric models, but apparently involved either peripatric or parapatric processes.

Incubation temperature in the Australasian Gannet Moms senator

Gannets (Sulidae) and some other pelecaniforms incubate their eggs under the webs of their totipalmate feet. These species have a wide latitudinal distribution from tropics to subarctic, but little is known of the incubation temperatures attained. I measured egg temperatures of the Australasian Gannet Morns serrator at Cape Kidnappers, New Zealand, employing a data logger to obtain records every 15 min for day‐long sample periods at undisturbed nests. Egg surface temperatures were relatively stable and little affected by ambient temperature. Mean surface temperature of natural eggs was 34.9oC for samples taken during the first 4 days of incubation, but this then increased and stabilized at 36.5oC. Internal temperature of pipped eggs was about 1oC higher, attributable to embryonic heat production. Upper surface temperature of eggs kept in a fixed position was about 2oC below deep adult body temperature (40.3oC), suggesting heat is transferred directly from the body through the feet. Clutch size does not appear to be limited by an inability to warm two eggs. These results are in general agreement with measurements from other web incubators and are well within the range for species with conventional brood patch incubation.

Plastics in Nests of Australasian Gannets Morus serrator in Victoria, Australia

(1995). Plastics in Nests of Australasian Gannets Morus serrator in Victoria, Australia. Emu - Austral Ornithology: Vol. 95, No. 2, pp. 129-133.

Aspects of the Breeding and Feeding Ecology of the Australasian GannetMorus serratorin Port Phillip Bay, Victoria, 1988–92

SummaryBreeding periodicity and success of Australasian Gannets Morus serrator were studied between 1988 and 1992 at two small colonies (Pope's Eye and Wedge Light), on artificial sites in Port Phillip Bay, Victoria. Samples of foods taken by adults (were collected for identification of major prey species. Banding of chicks and observations of adults previously banded as chicks (particularly at Wedge Light) provided information on the source of breeding adults and age of return to colonies. Wedge Light colony, established in 1966, has reached some 50 pairs: breeding there is now limited by available space. At Pope's Eye, where breeding began before 1985, space also limited breeding but the provision of an additional platform in 1989 led to a doubling of adults nesting (to c. 120 in 1991–92). Nest building at the study sites began in August-September, and eggs were laid mainly in September; second, or replacement, eggs from November-December. Most hatching took place October-November, with chicks fledging January-February; there was some variation in timing between years. Numbers of clutches laid, as a proportion of nest attempts, were consistently higher at Wedge Light; at Pope's Eye some nests were lost presumably as a result of bad weather. Hatching success was similar at both sites (64%), some 89% of chicks hatched left the platforms; mean breeding success (chicks fledged/eggs laid) was 57%. Although relatively few chicks died or were lost (9–14%), about 36% of eggs failed to hatch (mainly through loss). Nest success was influenced, to some extent, by exposure, particularly at Pope's Eye where seas may wash over breeding sites and drainage is poor. The extended breeding period may reflect local weather conditions and less reliable food availability. In this study, individual prey items were mainly Pilchards Sardinops sagax (58.4%); other taxa (20 fish, four cephalopods and a shrimp species) were generally represented by a few individuals. On average, prey species weighed 45 g, were 141 mm long, 15 mm wide and 26 mm deep; Pilchards were mostly (72%) < 140 mm long. Most regurgitations collected (mean mass 146 g) contained only one fish species (82%). As in other dietary studies of gannets, prey species were primarily inshore, schooling and pelagic. Little is known of factors influencing the distribution or abundance of the prey species; food deliveries at breeding colonies were lighter than those reported elsewhere, which may indicate local foraging. At both sites, colonies have grown as a consequence, in part at least, of the recruitment of chicks fledged at Wedge Light. Expansion at Wedge Light is now impossible, and at Pope's Eye there is little additional area for breeding. The provision of more artificial platforms might further increase the local population.

Locational differences in metal concentrations in feathers of Australasian gannet (Morus serrator) in New Zealand

Levels of lead, cadmium, mercury, selenium, manganese and chromium were examined in breast feathers of Australasian Gannets (Morus serrator) from New Zealand waters, where they breed on coastal rocky stacks, islands, and occasionally coastal headlands. There were significant differences in the concentrations of all metals except mercury, with gannets from Ninety Mile Beach having significantly lower levels of all metals than those from the other beaches. Ninety Mile Beach is on the northern tip of the North Island, away from urbanization and industrialization, whereas the other beaches are closer to Auckland, the largest city in New Zealand. The levels of most metals were similar or lower than those reported for feathers from elsewhere around the world. Mercury, however, was at the high end, being exceeded only by raptors and gulls from industrialized countries. Several metal levels were highly correlated, indicating that gannets were usually exposed to several metals at once.

Prey harvest of the Australasian gannet (Sula serrator) in Tasmania

This study investigated the diet of the Australasian gannet (Sula serrator) at Pedra Branca, an island off the south coast of Tasmania. A total of 109 regurgitations representing 394 prey items was collected from the gannets between 1986 and 1991. Pelagic schooling fish, with fork length less than 200 mm, were the most common prey items. Redbait (Emmelichthys nitidus) and jack mackerel (Trachurus declivis) were the dominant prey species, with redbait being the most numerous, contributing 72% by number and 56% by mass. The diet of the Australasian gannet was compared with the fish taken by the commercial purse seine fishery in which jack mackerel was the target species and redbait a bycatch. The mean size of commercially caught fish of both species was greater than that taken by the gannets. We suggest that there is a threshold (in the size of the fish) above which the birds cannot capture and handle the prey, effectively limiting the resource available to them. It appears that the commercial fishery and the gannets, while harvesting the same species, exploit schools of different-size fish. The potential of Australasian gannets as indicators of fish stocks is discussed.

Distribution and Abundance of Seabirds off Phillip Island and within Port Phillip Bay, Victoria, 1986–1988

Seabirds were counted along standard transect routes off Phillip Island and within Port Phillip Bay, Victoria. During these surveys 37 taxa were recognised, although only 10-11 were regularly seen. Of 25 taxa recorded within Port Phillip Bay, 16 were also included in the 28 seen off Phillip Island. Differences between sites related mainly to the occurrence of albatross species off the coast, and the variety of terns seen within Port Phillip. Off Phillip Island, most records were of Short-tailed Shearwater Puffinus tenuirostris which dominated the estimated biomass; in Port Phillip Bay the Silver Gull Larus novaehollandiae was numerically more important though the Australasian Gannet Morus serrator contributed more to the biomass. In general, areas off Phillip Island supported a higher average density and biomass than did those in Port Phillip Bay, primarily due to the seasonal influx of shearwaters during breeding periods. Commoner species, apart from cormorants and shags, were seen to the southem-most ends of transects run off Phillip Island. Main feeding methods are considered and it appears that the species occurring off Phillip Island are essentially polyvorous, taking a range of prey species, whilst most in Port Phillip are piscivorous.

Energy Requirements of Australasian Gannets Morus serrator (Gray) at a Breeding Colony

A model and empirical data (based on regurgitation weights from adult gannets and chicks) are used to estimate the energy requirements of the Australasian Gannet during the 1980-81 breeding season at Motukaramarama gannetry in the Hauraki Gulf, New Zealand. The model calculates the daily energy requirements of males, females, non-breeders and chicks using information from a study over three seasons (1978-80) at this gannetry. Output precision of the model is largely determined by a few parameters: the Kendeigh equation for daily existence energy requirements and the proportion of foraging time spent in flapping and gliding flight. The model suggests that two feeds are required per foraging trip to cover the costs of metabolism and rearing a chick. It is estimated that gannets take about 7% of fish production in the Hauraki Gulf within the 61 km² feeding range from Motukaramarama gannetry. This represents approximately a quarter to a third of total predation by seabirds on fish production.

Food and Feeding Range of the Australasian Gannet Morus Serrator (Gray)

SUMMARYWingham, E.J. 1985. Food and feeding range of the Australasian Gannet Morus senator (Gray). Emu 85: 231–239.Regurgitations analysed over three seasons (1978–80) indicated that Pilchards Sardinops neopilchardus, both numerically and by weight, were the most common prey species of the Australasian Gannet at Motukaramarama. The next most common species were: numerically, Anchovies Engraulis australis and by weight, Jack Mackerel Trachurus novaeselandiae. It is thought that relative abundance of prey analysed reflects their abundance. Prey between 11–20 cm comprised 77% of the Gannet's diet.A further two prey species: Sprat Sprattus antipodum and Kahawai Arripis trutta were recorded, bringing the known food of the Gannet to 15 species.The average adult Gannet regurgitated food equal to 11 % of its body weight (or 259 g and 2,000 Kj), whereas the average daily energy requirements were estimated at 2,844 Kj/day, or 353 g of food.An average feeding range of 268 km (range = 86–450 km) was estimated from the time adults spent away from the colony, resighting of marked birds and from recoveries of banded, breeding adults.

Breeding Biology of the Australasian Gannet Morus Serrator (Gray) at Motu Karamarama, Hauraki Gulf, New Zealand II. Breeding Success and Chick Growth

Hatching and fledging success in the Atlantic, Cape and Australasian Gannets were found to be similar (74-82% and 92-97%) at colonies where human disturbance was minimal. Australasian Gannet chicks suffer most from bad weather when very young. They fledge at about 108 days compared with 97 days for Cape and 90 days for Atlantic Gannets. Age at fledging was found to decrease as the season progressed but this trend may be due to human disturbance. Chick weights and growth measurements of known-age chicks are given. Australasian Gannets reach peak weight later than the other two species, this is 132% of adult weight in Australasian and Atlantic Gannets and 124% in Cape Gannets. Plumage development is shown in photographs and described.

Breeding Biology of the Australasian Gannet Morus Serrator (Gray) at Motu Karamarama, Hauraki Gulf, New Zealand I. the Egg

Breeding biology of the Australasian Gannet was studied over three breeding seasons (1978-80). The nest sites and density, first date and duration of egg-laying, median date of laying, clutch size and replacement laying, incubation period and egg dimensions, were measured. Similar information is available for the Atlantic Gannet and the Cape Gannet, allowing comparisons between the three Gannets to be made. The Australasian Gannet varies more in the first and median dates of laying than the Atlantic Gannet. This is thought to be related to weather and food supply. Most Australasian Gannet eggs that are lost are lost and replaced after three- quarters of the spread of laying has elapsed. In the Atlantic Gannet eggs are mostly lost and replaced before the mid-laying date. The Australasian Gannet has a proportionally larger egg than the Atlantic Gannet. These differences probablv result from the Australasian Gannet exoeriencing a less seasonal and predictable environment than the Atlantic Gannet.

Population Changes of the Australasian Gannet Morus Serrator(Gray) at the Motu Karamarama Gannetry, Hauraki Gulf, New Zealand

SUMMARYWAGHORN, E.J. 1983. Population changes of the Australasian Gannet Morus serrator (Gray) at the Motu Karamarama gannetry, Hauraki Gulf, New Zealand. Emu 82: 286–295.Population changes are discussed for Motu Karamarama (or Bush Island within the Motu Kawau Group), which is an established gannetry with little room for expansion. A visit was made to Mahuki gannetry, an island to the west of Great Barrier Island which, in contrast, had unlimited nesting space and was expanding rapidly.Diurnally, the maximum number of occupied nests occurred at 06:00 and it is possible to make a ‘time-of-day’ adjustment to counts made at other times.The intra-seasonal population variation reflected the breeding cycle. It was found that the maximum number of occupied nests did not correspond to similar stages in the breeding cycle from one season to the next. Diurnal and intraseasonal population changes noted from ground counts made on Motu Karamarama apply to similarly established gannetries only.Inter-seasonal population variation was found to be highly variable. This was partly because the timing of breeding in different seasons was unpredictable. Censuses at regular intervals (10 years) reflect the rate of colony growth or decline. Each gannetry was distinct from any other and no method was found from the study on Motu Karamarama that could be applied to data from other gannetries to give the maximum number of occupied nests.This study covered three seasons (1978–1980) but the population study concentrates on the last two seasons.