Differences in Diet and Chick Provisioning between Adult Roseate and Sandwich Terns in Puerto Rico

• Published in: The Condor (Los Angeles, Calif.) Calif.), 1998-02, Vol.100 (1), p.131-140
• Main Author: Shealer, David A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Autoecology; Aves; Biological and medical sciences; Boluses; Breeding; Chicks; Diet; Fish; Fish feeding; Fundamental and applied biological sciences. Psychology; Herring; Lagoons; Marine; Ornithology; Sardines; Species diversity; Sterna dougallii; Sterna sandvicensis; Vertebrata
• ISSN: 0010-5422; 1938-5129; 2732-4621
• DOI: 10.2307/1369904

I analyzed regurgitations from adult Roseate Terns (Sterna dougallii) and Sandwich Terns (S. sandvicensis) breeding in southwestern Puerto Rico in 1992 and 1993, and compared them with observations of prey delivered to chicks from 1991 to 1993 to determine similarities in the prey base for the two tern species during different stages in the breeding cycle, and differences between the diets of adults and chicks. I sampled prey fish at Turrumote lagoon where terns regularly fished to determine if the species composition of the fishes in the lagoon was representative of the prey base taken by terns. Adult Roseate Terns fed primarily on dwarf herrings (Jenkinsia lamprotaenia) and anchovies (Anchoa spp.), and fed chicks mostly dwarf herrings and sardines (Harengula and Opisthonema spp.); few anchovies were fed to chicks. Adult Sandwich Terns fed primarily on silversides (Hypoatherina harringtonensis) and sardines, and fed chicks mostly sardines and dwarf herrings; few silversides were fed to chicks. In 1992, both tern species apparently compensated for a lack of sardines by feeding their chicks proportionally more dwarf herrings. Diet diversity was greater for Sandwich than for Roseate Terns both in regurgitations and in prey delivered to chicks. Dietary overlap between the two species was low prior to, but converged following, chick hatching. Both species fed chicks increasingly larger prey as the chicks grew larger, but patterns were not consistent among years. Prey samples taken from Turrumote lagoon were representative of, but not in proportion to, the species of prey fed to chicks. These results indicate that although both Roseate and Sandwich Terns in Puerto Rico fed primarily on the same few species of fish, they did so in different proportions. This finding is consistent with an earlier study demonstrating foraging habitat segregation in these two species.