Plausible causes of seed preferences and diet composition in seed-eating passerines

LUIS MARONE; CUETO V; LOPEZ DE CASENAVE J; ZARCO A; CAMÍN S

JOURNAL OF AVIAN BIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2021

0908-8857

We evaluated whether seed mass, handling time, handling efficiency and profitabilityaccount for (a) preferences in controlled experiments and (b) field-diet compositionof four bird species of the Monte desert, Argentina. The question of whether birdsmaximise their energy intake rates while feeding on seeds is assessed. We used feeding experiments with six native seed species of 0.07?0.75 mg (i.e. the seed-size rangeconsumed in nature), which account for 0.59?0.84 of the field diet of the four birds.We measured seed-handling times and used published information on bird preferencesand diets, and on seed chemistry, for further calculations. Bird preferences were alwayspositively related to seed mass and also to seed profitability in the two intermediatesized birds. Diet composition correlated positively with seed mass and negatively withseed profitability in three species, but some birds also showed a flexible behavioureating the most attractive seeds according to their availability. This behaviour is notgenuinely opportunistic because it only focuses on a restricted fraction of the totalseed species present in the field. Contrary to expectations of species coexistence due toresource partitioning, small and large birds showed similar feeding efficiencies wheneating the smaller and the larger seeds. The positive association between seed massand profitability in several studies suggests that most birds can maximise their energyreward, on average and in the long-term, by preferring the larger seeds. A combinationof potential feeding optimisation with certain flexibility in the field may characterise the feeding ecology of desert seed-eating birds.