Effects of a hierarchal and spatially differential disruption of roosts and roost areas on non-random assorting (social) dynamic in bats using ephemeral forest conditions
March 2011 - December 2014
- Engineer Research Development Center Army 6.1 EQI
This study at Fort Knox, Kentucky, examines how disruption of primary (node) and secondary day-roosts affect the non-random assorting roost dynamic for the northern bat (Myotis septentrionalis). This species, similar to other forest-dwelling myotids, such as the endangered Indiana bat (Myotis sodalis) displays a cyclic spatio-temporal maternal colony system known as fission-fusion. Within this social structure, larger groups of bats, presumably matriline-dominated aggregates, may begin the maternity season at a single or a small number of centralized “node” roost trees as would be described via network analysis. Typically occurring in spatially-definable “roost-area, often these groups will disassemble into smaller groups and disperse to nearby secondary boles with periodic reassembly (in-part) at the centralized node tree in a scale-free network. The exact socio-behavioral mechanisms causing dispersal from node trees to secondary trees and back again are unknown. Nonetheless, the modularity of this system provides for various levels and combinations of nested patterns that allow bats and their conspecifics to gather and share relevant ecological information on roost location and availability within roost areas. Individual and group knowledge of roost location and availability is particularly important as suitable roosts such as snags or trees with cavities or other wounds often are ephemeral products of forest disturbance from fire, wind, flooding, drought, ice, and insect or disease damage. In many temperate forest conditions, these suitable roosts are ephemeral and therefore present in a shifting mosaic on the landscape that follows single-tree to stand disturbance or other processes such as stand senescence. The temporal scale of the disturbance return-interval dictates when roosts are created on the landscape. Longevity of roost suitability and multiple secondary roost acquisition by non-random aggregations serves to hedge bets against node loss within a season or between years for non-random assorting groups that are philopatric to defined roost areas. Such acquisition also serves as possible future node establishment, suggesting that the larger social group moves roost areas on the landscape in concert with disturbance and consequent shifting of suitable conditions. Understanding response to differential loss or accelerated availability of nodes and/or secondary roosts in a fission-fusion context should provide insights into how bats respond to extrinsic perturbations such as training and stewardship activities (short-term) or climate change (long-term). Conceivably, such information could be useful to implement forest management or ecological restoration actions that either will minimize impacts to extant roosting habitat or might enhance and expand roosting habitat. Perhaps more importantly, these data could allow managers the ability to place roosting habitat on the landscape where benefits to bats could be maximized while simultaneously reducing impacts of regulatory liabilities or impediments on landscape needs. OBJECTIVES: 1) removal of a node roost causes disassociation and reassembly at secondary roosts as novel social groups of northern bats on the landscape; 2)removal of secondary roosts lengthens node tree use and strengthens group cohesion; and 3) nonrandom assorting groups will switch roost areas if node and secondary roosts are simultaneously removed and new supplemental roosts are created.