Agriculture, cattle grazing, and human settlements negatively affect bird biodiversity, driving the loss of ecologically specialized species and favoring the dominance of generalists. Because ecological pressures define organisms' success by acting on their intrinsic traits, biodiversity loss due to anthropization might cause directional trait shifts. Here, we use a trait-based approach to find empirical evidence of trait-shifts in bird communities across an anthropization gradient in seasonal forests in central Mexico. We performed point-count bird surveys within a region of tropical deciduous and seasonal oak forests considering three degrees of anthropization: primary forest, secondary growth, and human settlements. A multivariate analysis (PCA) showed similar trait-covariation patterns for both forest types; in the anthropized habitat the bird communities exhibited shorter life-cycles, higher fecundity, and broader ecological niches (diet, foraging habitat, and nesting resources) than those in the primary forests. Our finding of directional trait shifts resembles Evolutionary Ecological Strategies Theory (EES) predictions for successful organisms within highly disturbed anthropized habitats, which are known as a “ruderal adaptative strategy” in the EES framework. The use of trait-based approaches could improve ecological generalizations in bird communities, leading to a better understanding of avian biodiversity's responses to anthropization.

SUPPLEMENTARY TABLE 1. Raw trait data of recorded resident bird species in seasonal tropical and oak forests in the Alto Balsas region, Guerrero.

For species in which life-history traits values were not available, we considered the phylogenetically closest species with available data. Where more than one value was available, we used the median of the available values.

Information sources for trait data are shown as numbers, and also are listed below. 

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SUPPLEMENTARY TABLE 2. Taxonomic list and raw abundance data of recorded resident bird species in seasonal tropical and oak forests in the Alto Balsas region, Guerrero.
Taxonomy follows American Ornithologist Society criteria (Chesser et al. 2021).

Raw abundance data are presented. The counts for each point event, forest type and anthropization level (primary forest = p; second-growth = sg; and human settlements = hs) are shown separately.

Chesser, R. T., S. M. Billerman, K. J. Burns, C. Cicero, J. L. Dunn, B. E. Hernández-Baños, A. W. Kratter, I. J. Lovette, N. A. Mason, P. C. Rasmussen, J. V. Remsen, Jr., D. F. Stotz, and K. Winker. 2021. Check-list of North American Birds (online). American Ornithological Society. http://checklist.aou.org/taxa

We carried out four series of bird counts between February 2014 and May 2016 in eight sites in the tropical and oak forests. We surveyed three sites in primary forest, three is secondary growth, and two in human settlements in each forest type. We amassed a total of 204 point-counts in the tropical forest (76 in primary forest, 72 in secondary growth, and 56 in human settlements), and 202 within the oak forest (72 in primary forest, 69 in secondary growth, and 61 in human settlements). Showed data are raw data abundace (recorded individuals).