title: Skylarks trade size and energy content in weed seeds to maximize total ingested lipid biomass.
abstract: The trade-off between forage quality and quantity has been particularly studied in herbivore organisms, but much less for seed eating animals, in particular seed-eating birds which constitute the bulk of wintering passerines in European farmlands. The skylark is one of the commonest farmland birds in winter, mainly feeding on seeds. We focus on weed seeds for conservation and management purposes. Weed seeds form the bulk of the diet of skylarks during winter period, and although this is still a matter for discussion, weed seed predation by granivorous has been suggested as an alternative to herbicides used to regulate weed populations in arable crops. Our objectives were to identify whether weed seed traits govern foraging decisions of skylarks, and to characterize key seed traits with respect to size, which is related to searching and handling time, and lipid content, which is essential for migratory birds. We combined a single-offer experiment and a multiple-offer one to test for feeding preferences of the birds by estimating seed intake on weed seed species differing in their seed size and seed lipid content. Our results showed (1) a selective preference for smaller seeds above a threshold of seed size or seed size difference in the pair and, (2) a significant effect of seed lipid biomass suggesting a trade-off between foraging for smaller seeds and selecting seeds rich in lipids. Skylarks foraging decision thus seems to be mainly based on seed size, that is presumably a 'proxy' for weed seed energy content. However, there are clearly many possible combinations of morphological and physiological traits that must play crucial role in the plant-bird interaction such as toxic compound or seed coat.
authors.affiliation: INRA, UMR1347 Agroécologie, 17 rue Sully, F-21065 Dijon Cedex, France. Electronic address: sabrina.gaba@dijon.inra.fr.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Gaba
authors.affiliation: INRA, UMR1347 Agroécologie, 17 rue Sully, F-21065 Dijon Cedex, France; INRA, UMR1213 Herbivores, Centre de Clermont-Ferrand/Theix, 63122 Saint-Genès-Champanelle, France.
authors.forename: Claire
authors.initials: C
authors.lastname: Collas
authors.affiliation: CEBC, UMR 7372 CNRS - Université de La Rochelle, F-79360 Villiers enBois, France; Office National de la Chasse et de la Faune Sauvage, Carrefour de la Canauderie, 79360 Villiers en bois, France.
authors.forename: Thibaut
authors.initials: T
authors.lastname: Powolny
authors.affiliation: Université de Bourgogne, UMR6282 Biogéosciences, 6 Boulevard Gabriel, 21000 Dijon, France; UMR 5175 CEFE-CNRS, 1919 Route de Mende, 34293 Montpellier 5, France.
authors.forename: François
authors.initials: F
authors.lastname: Bretagnolle
authors.affiliation: CEBC, UMR 7372 CNRS - Université de La Rochelle, F-79360 Villiers enBois, France; LTER « ZA Plaine & Val de Sèvre », CNRS-CEBC, F-79360, Beauvoir sur Niort, France.
authors.forename: Vincent
authors.initials: V
authors.lastname: Bretagnolle
mesh_terms: D000818:Animals; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D008055:Lipids; D008297:Male; D046109:Passeriformes / Q000502:physiology*; D012639:Seeds
chemical_list: D008055:Lipids
keywords: Lipid content; Optimal foraging; Seed size; Skylark; Trade-offs; Weed