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Abstract

We provide, for the first time, data on the breeding parameters of the Gull-billed Tern Gelochelidon nilotica in Tunisia, at Boughrara Lagoon. From May to July 2024, we monitored a breeding colony located on a small islet in the northern part of the lagoon. In total, 112 nests were monitored: 71 nests initiated in mid-May (early clutches) and 41 in early June (late nests). Clutch size ranged from one to four eggs (mean ± standard deviation [SD] = 2.51 ± 0.06), with no significant difference between early and late nesters. Egg volume ranged from 14.65 to 49.23 cm3 (mean ± SD = 27.56 ± 4.03) and did not vary with laying date. However, egg volume decreased significantly with laying order across all nests. Last-laid eggs were smaller than first-laid eggs, consistent with a brood reduction strategy, which is a common breeding strategy in terns. Only 15% of nests failed to produce chicks, but the causes of failure could not be determined precisely. No evidence of egg predation was recorded, and failures were likely due to conflicts between neighboring pairs. Early nests were more successful than late nests (94% vs. 76%). This seasonal decline in reproductive success is consistent with general trends in waterbirds and may reflect either lower intrinsic quality of late breeders or deterioration of environmental conditions late in the breeding season.

DOI

http://doi.org/10.5038/2074-1235.54.1.1689

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