Context
Nest location is an important determinant of reproductive success in many seabirds. Better understanding of breeding ecology of threatened seabirds could help in their conservation.
Aims
We evaluated nest location and reproductive success in the globally Vulnerable, regionally endemic, Socotra cormorants on Siniya Island, United Arab Emirates, in relation to multiple habitat factors to assess the relative influence of each.
Methods
We measured hatching success, as an indication of reproductive success, on 14 study plots during the 2011–12 breeding season. We measured distances from each study plot to the nearest tree, road, predation area, sandy beach and lagoon. We used multiple logistic regression to determine the extent to which these explanatory factors influenced hatching success. We used an information theoretic approach to select the best model.
Key results
Hatching success was significantly related to tree cover, distance from beach and distance from heavily depredated areas (AICc weight = 0.613). Nests were significantly deeper (13.14 ± 0.35 cm) in unshaded areas compared with areas shaded by trees (10.8 ± 0.31 cm) (ANOVA: F2,12 = 24.93, P < 0.001).
Conclusions
Thus, we conclude that shade provided by planted non-native trees is an important factor affecting nest location and hatching success. Deeper nests could aid incubation by lowering nest temperatures during peak incubation periods (August) when temperatures may exceed 48°C. Heavy predation pressure is affecting hatching success. Wind action could be preventing nesting near the sandy beach.
Implications
Planted non-native trees are advantageous to breeding Socotra cormorants, although planting trees is not advocated. High predation pressure from feral cats and red foxes is reducing hatching success of Socotra cormorants on the largest known colony in the United Arab Emirates. Feral cats should be eradicated whereas the red foxes could be managed as a precautionary measure to ensure the continued survival of this threatened seabird.
Historically cormorants have come into direct conflict with fisheries because of their feeding habits. The Socotra cormorant Phalacrocorax nigrogularis is a regionally endemic seabird restricted to the Arabian Gulf and coastal Oman, and is categorized as Vulnerable on the IUCN Red List. The species is perceived as being detrimental to local fisheries and is therefore persecuted. We studied the diet and estimated the number of Socotra cormorants breeding on Siniya Island, Umm Al Quwain, United Arab Emirates, to determine their impact on local fisheries. Regurgitated fish loads were collected during the breeding seasons of - and -, and the biomass of fish consumed by the Socotra cormorant population was estimated. The diet comprised seven species of fish, with sailfin flying fish Parexocoetus mento and blue-stripe sardine Herklotsichthys quadrimaculatus dominating in - and anchovies (Encrasicholina spp.) dominating in -. Biomass of fish loads was higher in - compared to -, although mean biomass of fish loads did not differ. Dominant fish species in the cormorant's diet were either used as baitfish or were non-target species in the fisheries. The low overlap between the diet of the Socotra cormorant and the fish landed by the fisheries suggests that the cormorant's impact on fisheries is minimal. Conservation strategies to protect the birds and their feeding areas could safeguard populations of this species from further declines.
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