We assessed the effects of quality and quantity of prey species on the
growth of Little Tern Sterna albifrons chicks raised in salinas (salt-pans),
Algarve, Portugal. An energetic balance model was developed, which
estimated the total amount of energy ingested by all chicks in a nest and
the energy expenditure by the chicks when either growing alone or in
groups of two and three per nest. Energy intake per chick depended on
the energy available per nest and a competition value for food between
chicks. Energy expenditure was defined by the basal metabolic rate
(BMR), which depends on chick\u2019s weight, plus a multiple of BMR,
obtained by calibration and accounting for unspecified energetic losses.
Prey species ingested by Little Tern chicks were mainly the fishes sand-
smelt Atherina spp., Sardine Sardina pilchardus, Garfish Belone belone
and mummichog Fundulus spp., but also two types of shrimp (Paleo-
monetes spp. and Paleomon spp.). Although prey species more abundant
in salinas (shrimps and Fundulus spp.) were delivered at a higher rate,
and Fundulus spp. had the greatest calorific content, chick growth was
more sensitive to alterations in the ingestion of typically marine fish
species, such as Sardina pilchardus and Belone belone. Model predictions
were in agreement with data obtained in the field, as adults breeding in
salinas foraged regularly at sea. Practical considerations from the pre-
sent results are: (1) birds breeding in salinas rely on a sufficient amount
of typically marine prey to ensure the growth of their chicks; (2) in
some years foraging conditions in the salinas can be favourable, appar-
ently because high food abundance (plus proximity to nests) may com-
pensate for relatively poor quality of food types encounteredFCT Project POCTI/BSE/37385/200
