Birds’ gap-crossing in open matrices depends on landscape structure, tree size, and predation risk

Abstract Scattered trees are frequently considered “keystone structures” due to their disproportionate contribution in facilitating movement across the landscape. However, which landscape structure scattered trees best facilitate animal movement in the most effective manner remains poorly understood in the literature. Here, we tested three hypotheses examining how scattered trees influenced natural bird movement across an open matrix. We used three bird sampling methods: line transect, point count, and focal tree sampling. Our results showed that the efficacy of scattering trees as stepping stones and/or as a source of resources is mainly conditioned by three factors: predation risk, tree size, and landscape context in which the trees are inserted in an open matrix. In general, movement between habitat patches (gap-crossings) were more frequent in shorter distances (mean = 10.9 m). For larger gaps, the addition of scattered trees as stepping stones in the movement path is essential in reaching the neighboring habitat patches. The functional drivers of scattered trees are mainly related to perching, eating, and reproducing. Their functions increase with tree size and distance to the nearest patch. In relation to landscape context, birds prefer scattered trees surrounded by higher amounts of forest cover or with a network of higher aggregation trees. All these decision-making outcomes suggest antipredatory strategies during bird movement across landscapes including: (1) reducing the distance required to reach safer shelter; (2) choosing larger scattered trees as stepping stones, which improves a birds’ ability to detect predators, before deciding on the next movement; (3) choosing the movement path in the landscape context that most reduces the ability of predators to detect them or that increases the probability of escape from a predator. Land managers who wish to facilitate bird movements in open matrices should ensure gaps between landscape elements are less than 40 m; preserve and actively plant arboreal individuals of tree species (height > 15 m) in open matrices; increase spatial aggregation of scattered trees or use them in landscapes with higher amounts of forest cover.