Agricultural intensification is a key factor in the decline of many avian populations throughout the world, yet the exact mechanisms that contribute to these declines are relatively unresolved, especially for seed-eating species. We tested the hypothesis that forage quality, particularly protein content, limits productivity in birds consuming diets dominated by agricultural grains and lacking in native forages. We used white-winged doves (Zenaida asiatica) because columbids are highly granivorous and white-winged doves have declined in areas dominated by grain agriculture. We randomly assigned 52 pairs of captive doves to 1 of 2 treatments: we fed one treatment sorghum (Sorghum bicolor) and the second sorghum plus native seeds (croton [Croton sp.] and native sunflower [Helianthus sp.]). Birds with access to native seeds fledged 123% more young per pair, with young weighing 32% more at fledging than those fed only sorghum. Doves with access to native seeds selected a diet consisting of 43% sorghum, 32% croton, and 25% sunflower. We conclude that agricultural grains, which typically have high metabolizable energy and low to moderate protein concentrations, are not sufficient for normal productivity of white-winged doves. The lack of native forages with sufficient metabolizable energy and protein content may be a factor in the declining productivity of white-winged doves in the lower Rio Grande Valley of Texas, USA, as well as other species in regions dominated by agriculture.
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Vol. 72 • No. 2