Abstract
Foliage echoes could play an important role in the sensory ecology of echolocating bats, but many aspects of their sensory information content remain to be explored. A realistic numerical model for these echoes could support the development of hypotheses for the relationship between foliage properties and echo parameters. In prior work by the authors, a simple foliage model based on circular disks distributed uniformly in space has been developed. In the current work, three key simplifications used in this model have been examined: (i) representing leaves as circular disks, (ii) neglecting shading effects between leaves, and (iii) the uniform spatial distribution of the leaves. The target strengths of individual leaves and shading between them have been examined in physical experiments, whereas the impact of the spatial leaf distribution has been studied by modifying the numerical model to include leaf distributions according to a biomimetic model for natural branching patterns (L-systems). Leaf samples from a single species (leatherleaf arrowwood) were found to match the relationship between size and target strength of the disk model fairly well, albeit with a large variability part of which could be due to unaccounted geometrical features of the leaves. Shading between leaf-sized disks did occur for distances below 50 cm and could hence impact the echoes. Echoes generated with L-system models in two distinct tree species (ginkgo and pine) showed consistently more temporal inhomogeneity in the envelope amplitudes than a reference with uniform distribution. However, these differences were small compared to effects found in response to changes in the relative orientation of simulated sonar beam and foliage. These findings support the utility of the uniform leaf distribution model and suggest that bats could use temporal inhomogeneities in the echoes to make inferences regarding the relative positioning of their sonar and a foliage.
Highlights
Many echolocating bat species can navigate [1,2,3] in dense vegetation and find insect prey or other foods such as nectar [4] and fruit [5] among foliage based on information obtained from ultrasonic biosonar echoes [6]
The acoustic measurements conducted on the disc pairs demonstrated the existence of acoustic interaction effects between leaves that depended on the distance between the discs (Fig 5)
While highly consistent, these differences were very small compared to the changes in temporal homogeneity seen as a result of varying the relative position of the sonar beam and the foliage
Summary
Many echolocating bat species can navigate [1,2,3] in dense vegetation and find insect prey or other foods such as nectar [4] and fruit [5] among foliage based on information obtained from ultrasonic biosonar echoes [6]. The nature of foliage echoes is likely to play a critical role in the function of the biosonar system of bats that occupy such sensori
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