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Accueil du site → Doctorat → États-Unis → 2010 → Influence of seed resources on the diet, seed selection, and community dynamics of wintering birds in semi-arid grasslands

NEW MEXICO STATE UNIVERSITY (2010)

Influence of seed resources on the diet, seed selection, and community dynamics of wintering birds in semi-arid grasslands

Mendez-Gonzalez, Cesar Ernesto

Titre : Influence of seed resources on the diet, seed selection, and community dynamics of wintering birds in semi-arid grasslands

Auteur : Mendez-Gonzalez, Cesar Ernesto

Université de soutenance : NEW MEXICO STATE UNIVERSITY

Grade : Doctor of Philosophy (PhD) 2010

Résumé partiel
Grassland bird populations have declined dramatically during recent decades. Habitat loss has been a major contributing factor in population declines. However, little is known about the importance of winter habitat quality and the effects of seed distribution, abundance, and diversity on sparrow communities remain to be understood. I examined the diets of winter sparrows under natural conditions at grassland sites in southern New Mexico and southeastern Arizona over three winter periods (2003-2005) and explored factors affecting seed selection. I collected over 900 avian diet samples of 21 bird species across 7 different sites. Seeds in avian diets and soil seed bank samples were diverse (> 65 and > 95 species respectively). In some cases the most abundant seeds in the soil were the most consumed seeds by birds. However in many cases seeds most selected were not the most abundant in the soil bank. Despite the large diversity of seeds found in avian diets and soil, only a few species contributed greatly to overall seed biomass (> 80%). The most important seeds found in avian diets were Sporobolus spp., Mollugo verticillata, Eragrostis spp., Amaranthus spp., Chloris virgata , and Chenopodium spp. Small-bodied sparrows specialized on small-sized seeds whereas larger-bodied sparrows exhibited preferences for smaller and larger seeds. Sparrows possibly selected smaller seeds because they may have been more profitable in terms of energy gain due to their high abundance and detectability, quick handling and swallowing, and more efficient digestibility. I evaluated the influence of Eragrostis lehmanniana on avian relative abundance in grasslands of southeastern Arizona. During two winter seasons (2004-2005) I compared avian relative abundance, community composition, and diet of sparrows overwintering in two adjacent grassland patches, one co-dominated by native grasses and E. lehmanniana (Mixed) and the other dominated by E. lehmanniana (Exotic). Total canopy cover, E. lehmanniana cover, maximum vegetation height, and visual obstruction were greater at the Exotic compared to the Mixed site in both winters. E. lehmanniana cover doubled at the Mixed site over the one-year interval.

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Page publiée le 3 novembre 2013, mise à jour le 21 décembre 2019