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Australasian Gannet - Morus serrator
Topic Started: Feb 11 2018, 01:49 PM (328 Views)
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Australasian Gannet - Morus serrator

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Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Suliformes
Family: Sulidae
Genus: Morus
Species: Morus serrator Gray, 1843

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Australasian gannet range

The Australasian gannet (Morus serrator), also known as Australian gannet and Tākapu, is a large seabird of the gannet family Sulidae.

Adults are mostly white, with black flight feathers at the wingtips and lining the trailing edge of the wing. The central tail feathers are also black. The head is yellow, with a pale blue-grey bill edged in black, and blue-rimmed eyes.

Young birds have mottled plumage in their first year, dark above and light below. The head is an intermediate mottled grey, with a dark bill. The birds gradually acquire more white in subsequent seasons until they reach maturity after five years.

Their breeding habitat is on islands and the coast of New Zealand, Victoria and Tasmania, with 87% of the adult population in New Zealand. They normally nest in large colonies on coastal islands. In New Zealand there are colonies of over 10,000 breeding pairs each at Three Kings Islands, Whakaari / White Island and Gannet Island. There is a large protected colony on the mainland at Cape Kidnappers (6,500 pairs). There are also mainland colonies at Muriwai and Farewell Spit, as well as numerous other island colonies.

Gannet pairs may remain together over several seasons. They perform elaborate greeting rituals at the nest, stretching their bills and necks skywards and gently tapping bills together. The adults mainly stay close to colonies, whilst the younger birds disperse.

These birds are plunge divers and spectacular fishers, plunging into the ocean at high speed. They mainly eat squid and forage fish which school near the surface. It has the same colours and similar appearance to the Northern Gannet.

Numbers of Australasian gannet have been increasing since 1950, although some colonies have disappeared and others have decreased in size.

The lonely life of Nigel the gannet wasn't in vain
The bird's presence was a poignant conservation love story.

February 5, 2018, 2:09 p.m.

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Nigel stands with the stone birds that made up his adopted 'colony' on Mana Island. (Photo: Gecko Lover/YouTube)

Nigel, a gannet who resided on New Zealand's Mana Island, lived as he died, surrounded by concrete "friends."

Ranger Chris Bell discovered the body of the gannet in late January, just weeks after three more gannets had arrived on the island.

"It seems like such a wrong ending for Nigel to die now,” Bell told The New York Times. "Just when it looked like it could get better for him."

Nigel and the real bird

In the 1990s, conservationists added some 80 decoy gannets to the island in an effort to attract actual gannets to the island. Their efforts were unsuccessful until some time between 2013 and 2015 — conservationists differ on the year — when a lone gannet arrived on the island. Nigel became the first gannet to call Mana Island home in 40 years.

The arrival of Nigel was cause for celebration and then concern as conservationists realized that not only was Nigel alone but that he was head-over-wings in love with one of the stone decoys that had attracted him to the island in the first place.

Nigel was observed caring for the concrete replica. He would groom the statue and chat with it; Nigel even constructed a nest made of twigs, seaweed and mud for it.

Naturally, the decoy never reciprocated Nigel's overtures.

"I think the saddest part of this story is what a frustrating existence to be courting this stone bird and getting nothing back," Bell told The Times. "Not getting rejected, not getting encouragement."

Revitalizing an island

Those three other gannets that arrived weren't much help in getting Nigel to come to his senses. They mostly kept to themselves on the other end of the colony, and Nigel, for his part, didn't seem interested in leaving his "lover."

However, their presence is a testament to the value of Nigel staying with his concrete paramour.

"From a conservation point of view, he was a massive asset to have. Because the concrete gannets — they may have fooled Nigel — but they never fooled another gannet. We always considered Nigel increased our chances of getting a colony going, and that seems to be in the end what happened," Bell explained to the Guardian.

The attempt to get gannets back to Mana Island is one of several seabird projects currently underway in and around New Zealand, and it's part of a wider initiative to bring native wildlife back to places that had been overrun by invasive predators.

Mana Island is now pest-free and has been repopulated with 500,000 native trees, lizards and other seabirds. The seabirds, in particular, are important to the island's ecosystem as they provide nutrients for the soil and for insects, reports the Times.

The decoys, along with solar-powered speakers that pipe out seabird calls, are scattered in small "colonies" around the island. They're intended to encourage gannets to settle on the island since gannets prefer to nest in areas where other gannets have already established a foothold.

In that sense, Nigel's lonely existence may not have been in vain.

"He was an attraction that helped bring in other birds — gannets like to nest where a gannet has nested before," Bell said. "It's really sad he died, but it wasn't for nothing."

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Nutritional quality of fish and squid reduced by warm water events

June 8, 2018, University of Sydney

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Australasian gannet in flight. Credit: Gabriel Machovsky-Capuska

Research led by the University of Sydney shows that under warm water events the nutritional balance of fish and squid changes and is of lower quality, while under cold water events it is of higher quality.

Conducted in New Zealand, the research used a highly successful marine predator seabird -the Australasian gannet—as a biological monitor of the marine environment and food sources.

The team combined miniature bird-borne GPS loggers, fish and squid nutritional analysis and nutritional modelling, and quantified colder and warmer water events by comparing the mean sea surface temperature with 10 years of data.

Fish and squid captured by gannets were found to have significantly lower ratio of healthy oils to protein during warm water events (where sea surface temperature was warmer than the 10-year mean) and better nutritional quality during cold water periods (lower than the 10-year mean).

Published in the Journal of Animal Ecology, the research was a collaboration between the Charles Perkins Centre, School of Life and Environment Sciences and School of Mathematics and Statistics at the University of Sydney; James Cook University in Queensland; Massey University in New Zealand; and the Ornithological Society of New Zealand. It forms part of the human-animal interactions and Human Food Chain project nodes at the Charles Perkins Centre.

Lead author Dr. Gabriel Machovsky-Capuska, adjunct senior researcher at the University of Sydney's Charles Perkins Centre, said the findings had implications for marine life and its predators, including humans.

"Marine mammals and seabirds such as gannets eat similar foods as humans—namely fish and squid," he explained.

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Australasian gannet. Credit: Gabriel Machovsky-Capuska

"All capture prey in similar areas, and inevitably all are impacted by nutritional changes to this food source."

Co-author Professor David Raubenheimer, the University of Sydney's Leonard P Ullmann Chair in Nutritional Ecology at the School of Life and Environmental Sciences and Charles Perkins Centre, said the research team devised a novel approach in order to conduct the research.

"Our approach, which we call nutritional landscapes, allows us to associate the nutritional quality of marine resources—otherwise very challenging, as marine life continuously moves—with geographic location, water depth and environmental conditions such as sea surface temperature and chlorophyll levels," Professor Raubenheimer explained.

"These findings underline the importance of linking marine environmental fluctuations with the nutritional quality of fish and squid for human consumption—and provide significant insights for fisheries that are capturing fish for humans to eat."

Dr. Machovsky-Capuska said the findings were also revealing for environmental and conservation purposes.

"The work shows that diet and foraging behaviour of marine predators are significantly influenced by warm and cold events," he said.

"During warm water events gannets had to work harder for their food as they expanded their foraging habitat and increased their foraging trip duration, while at the same time consuming prey and diets with lower content of energy-providing oils," he said.

"Our approach can be used to understand and ultimately protect travelling routes for migratory species, and could support the conservation of endangered species in terms of food quality and habitat suitability."


Journal Reference:
Gabriel E. Machovsky-Capuska et al, The nutritional nexus: linking niche, habitat variability and prey composition in a generalist marine predator, Journal of Animal Ecology (2018). DOI: 10.1111/1365-2656.12856

1.Our understanding of the niche concept will remain limited while the quantity and range of different food types eaten remains a dominant proxy for niche breadth, as this does not account for the broad ecological context that governs diet. Linking nutrition, physiology and behaviour are critical to predict the extent to which a species adjusts its nutritional niche breadth at the levels of prey (“prey composition niche”, defined as the range of prey compositions eaten), and diet (“realized nutritional niche” is the range of diets composed through feeding on the prey).

2.Here we studied adult‐chick rearing Australasian gannets (Morus serrator) to propose an integrative approach using sea surface temperature anomalies (SSTa), geographic location and bathymetry over different years, to explore their relationship with the nutritional composition of prey and diets (i.e., prey composition and nutritional niche breadth), habitat use and foraging behavior.

3.We found that gannets feed on prey that varied widely in their nutritional composition (have a broad prey composition niche), and composed diets from these prey that likewise varied in composition (have a broad realized nutritional niche), suggesting generalism at two levels of macronutrient selection.

4.Across seasons, we established “nutritional landscapes” (hereafter nutriscapes), linking the nutritional content of prey (wet mass protein to‐lipid ratio ‐P:L‐) to the most likely geographic area of capture and bathymetry. Nutriscapes varied in their P:L from 6.06 to 15.28, over time, space and bathymetry (0 to 150 m).

5.During warm water events (strong positive SSTa), gannets expanded their foraging habitat, increased their foraging trip duration and consumed prey and diets with low macronutrient content (wet mass proportions of P and L). They were also constrained to the smallest prey composition and realized nutritional niche breadths.

6.Our findings are consistent with previous suggestions that dietary generalism evolves in heterogeneous environments, and provide a framework for understanding the nutritional goals in wild marine predators and how these goals drive ecological interactions and are, in turn, ultimately shaped by environmental fluctuations.

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