1. Tree diversity can exert a strong influence on consumers, but most studies have involved short-term assessments. Consequently, we have a limited understanding of temporal variation in the effects of tree diversity on multi-trophic communities and thus how tree diversity impacts ecological function.

2. We conducted a year-long study in an experimental system in southern Mexico assessing the effects of tree diversity on the abundance and diversity of visiting birds. To this end, we recorded bird visitation patterns for 32 plots (21 × 21 m; 12 monocultures, 20 four-species polycultures) every 45 days (n = 8 surveys) and for each plot estimated bird abundance, richness, functional diversity (FD), and phylogenetic diversity (PD). In each case, we reported temporal (intra-annual) variation in the magnitude of such diversity effects, and calculated the temporal stability of these bird responses.

3. Across surveys, tree diversity noticeably affected bird responses, demonstrated by significantly higher abundance (43%), richness (32%), PD (25%), and FD (25%) of birds visiting polyculture plots compared to monoculture plots, as well as a distinct species composition between plot types. We also found some degree of intra-annual variation in diversity effects on these response variables, ranging from surveys for which the tree diversity effect was not significant to surveys where a significant 80% increase (e.g. bird FD and PD) was observed in polyculture relative to monoculture plots. Notably, tree diversity increased the stability of all bird responses, with polycultures having a greater stability abundance (18%), richness (38%), PD (34%), and FD (32%) of birds visiting polycultures compared to monocultures.

4. These findings show that tree diversity not only increases bird visitation to plots, but also stabilizes bird habitat usage over time in ways that could lead to insurance-related mechanisms. These results are highly relevant for understanding the long-term effects of plant diversity on vertebrates and the persistence of bird-related ecosystem functions. Accordingly, more work is needed to unveil the ecological mechanisms underlying temporal variation in vertebrate responses to tree diversity and their consequences for community structure and function.

Visual bird surveys were conducted for monoculture and polyculture tree plots ca. every 45 days during a one-year period from February 2017 to January 2018. Each survey lasted one week, during which each plot was observed for 20 minutes on three different occasions during that survey. A total of eight surveys were conducted throughout the study year.