Feeding ecology of the Common Tern Sterna hirundo in a wintering area in southern Brazil

Abstract

The wintering diet of Common Terns Sterna hirundo was studied by using 714 pellets collected on roosting sites at the mouth of the Lagoa dos Patos and on adjacent coastal beaches, in Rio Grande do Sul, southern Brazil, from March 1999 to February 2000. A total of 12 340 individual prey items of 35 different food types was found. Fish was the most important food type in the diet, constituting 32% by number and 93% by mass. Insects contributed 67% by number but only 3% by mass. The main food types were sciaenid fishes Paralonchurus brasiliensis, Micropogonias furnieri, Cynoscion guatucupa and Macrodon ancylodon. Several of these are important commercial species; fisheries potentially impact food availability to the terns, and terns may contribute significantly to the natural mortality of these fishes. Clupeiform fishes, the urophycid fish Urophycis brasiliensis and flying ants (Camponotus sp.) were also important. Species composition of the diet (food types), both by number and by mass, differed significantly between months. Prey sizes ranged in length from 12.7 mm to 217.4 mm. The average estimated total length of fish taken was 77.7 mm, but the mean differed significantly among prey species. The importance of demersal sciaenids to the diet of the Common Tern, a surface predator, may be explained by their association with aquatic predators, especially adult Bluefish Pomatomus saltatrix and Striped Weakfish Cynoscion guatucupa, and the Franciscana Dolphin Pontoporia blainvillei, which drive these fish to the surface. The occurrence of flying ants in the diet was related to offshore winds, which carried these insects out to sea. The occasional high availability of insects possibly changed the cost/benefit relationship of several food types, causing diet changes. The high number of prey species, the temporal variations in the composition of the diet and the wide range of prey sizes are evidence of the high dietary plasticity of the Common Tern, at wintering areas in southern Brazil.

Abundance, breeding and food of the Little Blue Heron Egretta caerulea (Aves, Ardeidae) in the Patos Lagoon estuary, a recently colonized area in southern Brazil

“…A prey taxon present in the sample is termed a 'food item', and for each food item an individual animal in the sample is termed a 'prey' (BuGoni & vooren, 2004). Total length of all fish and shrimp (TL, mm) was measured, while for crabs the carapace width (CW, mm) was measured.…”

“…The parameters determined for each food item were its frequency of occurrence (absolute FO and relative FO, %), its number of ingested preys (absolute and relative N), its reconstructed mass (absolute and relative M) and its Index of Relative Importance (IRI), as modified by BuGoni & vooren (2004) Thus, more adult herons were observed in the Tamandaré roost than in the breeding colony, and more juveniles were observed in the breeding colony than at the roosting site (Fig. 2).…”

Impacts of climate variation and potential effects of climate change on South American seabirds – a review

“…The seasonally high productivity results in a considerable biomass of potential seabird prey (for, e.g. common tern Sterna hirundo Linnaeus, 1758: Bugoni & Vooren 2004), such as small pelagic fish, especially orangespot sardine (Sardinella brasiliensis (Steindachner, 1879)) and anchovy, pelagic juvenile stages of demersal fish species and flying fish Cypselurus sp. (for, e.g.…”

Eye fluke-induced cataracts in natural fish populations: is there potential for host manipulation?

“…After determining the coverage of cataracts, we dissected the eye lenses to count the Diplostomum metacercariae in them, and measured the length of each fish (± 1 mm). Since we were only interested in fish suitable in size for avian predation (definitive hosts of the parasites), we did not consider fish longer than 200 mm (see Bugoni and Vooren, 2004;Mauco and Favero, 2004). From a total of 30 fish, we could not determine either cataract coverage or parasite abundance and we excluded them from the data.…”