Segregation in diet between Black Noddy (Anous minutus) and Brown Noddy (A. stolidus) from the Southern Lagoon of New Caledonia

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Date: Apr. 2015
From: Pacific Science(Vol. 69, Issue 2)
Publisher: University of Hawaii Press
Document Type: Report
Length: 3,819 words
Lexile Measure: 1400L

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Abstract: The Black Noddy (Anous minutus) and the Brown Noddy (A. stolidus) occur sympatrically in the Southern Lagoon of New Caledonia, breeding on islets located at the edge of a wide, productive coral-reef lagoon next to oceanic waters enriched by a seasonal upwelling. The diets of the two species were determined from regurgitations from birds nesting at Kouare Islet during two consecutive breeding seasons (2002/2003 and 2003/2004) and compared. The average prey load in the Brown Noddy was heavier than that in the Black Noddy, as expected from its larger body size and from a predicted longer foraging distance. Fish prey dominated the diet of both species (100% and 81.8% biomass in Black and Brown Noddies, respectively); the remainder consisted of squid. Black Noddy ate small pelagic fishes inhabiting the reef and the lagoon, mainly round herrings (Spratelloides spp.), and Brown Noddy mainly preyed on offshore species including buccaneer anchovy (Encrasicholina punctifer) and larger pelagic fishes (Exocoetidae) and squids. The segregation in diet between Black and Brown Noddies in New Caledonia thus indicated spatial segregation in foraging zones (i.e., inshore versus offshore, respectively), which was more pronounced than previously reported for other sites where the two species co-occur.

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The Black Noddy (Anous minutus) and the Brown Noddy (A. stolidus) have tropical distributions; the latter is pantropical. Much of their ranges overlap, except in the Indian Ocean, where the Black Noddy is replaced by its slightly smaller sister-species, the Lesser Noddy (A. tenuirostris) (Higgins and Davies 1996, Bridge et al. 2005). Noddies depend for feeding on large marine predators, particularly tunas: tunas prey on schools of small pelagic fishes by concentrating them toward the surface before going through the school to catch them (Ashmole 1962, Hulsman 1988). Noddies catch their prey either by dipping or, though more rarely, by surface plunging (Chardine and Morris 1996, Gauger 1999). Brown Noddy may also catch fishes in the air (Ashmole 1971).

Brown and either Black or Lesser Noddies breed in sympatry in a number of localities, although usually one species largely outnumbers the other (Dorward and Ashmole 1963, Ashmole and Ashmole 1967, Harrison et al. 1983, Surman and Wooller 2003, Ramos et al. 2006). In the Southern Lagoon of New Caledonia (Southwest Pacific Ocean) (Figure 1), the Black Noddy (A. minutus minutus) outnumbers the Brown Noddy (A. stolidus pileatus) by ca. 60,000 pairs to ca. 1,000 pairs (Pandolfi-Benoit and Bretagnolle 2002). Although the Southern Lagoon comprises more than 55 islets, the Black Noddy breeds on only six of them, five of which are also nesting sites for the Brown Noddy (Figure 1).

We analyzed the diet of Black and Brown Noddies breeding in sympatry and in synchrony, choosing an islet of the Southern Lagoon of New Caledonia as the study site. Several predictions on prey composition can be made on the basis of morphological differences between the two species. Although bill length is similar in Black and Brown Noddies (Higgins and Davies 1996), it is thicker in the Brown Noddy, enabling it to grab...

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Gale Document Number: GALE|A424989698