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Volume 101, Issue 3 e01700
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Open Access

Time-Averaging Voles Match Density with Long-Term Habitat Quality

First published: 07 July 2020

Study Description

Theory predicts that optimally foraging animals should match their abundance with long-term habitat quality. I tested the prediction with experiments on meadow voles (Microtus pennsylvanicus) living in 0.25-ha field enclosures. Voles could remain in an enclosure with constant resource renewal or disperse to one with a predetermined schedule of varying quality. I assessed foraging gain with giving-up densities, and foraging times of RFID-marked rodents, in automated risky versus safe foraging trays. Data were consistent with only one of four hypotheses. Voles averaged spatial heterogeneity in a way that enabled a match with the long-term mean quality of different habitats.

Photo 1. The Lakehead University Habitron in northern Ontario, Canada. The Habitron consists of 24 interconnected rodent-proof enclosures, a small office, outdoor field laboratory, and three storage sheds. Enclosures have small gates that can be opened to enable dispersal among habitats. Field biologists control rodent densities, age distributions and sex ratios, and determine whether enclosures receive supplemental resources, and whether animals can move from one enclosure to others. Photo credit: Douglas Morris.


Photo 2. Circular foraging trays used to calculate giving-up densities (GUDs) located under a clear polyethylene cover (risky foraging site) and a nearby plywood cover (safe foraging site). Trays are filled with 1.5 L of sieved silica sand thoroughly mixed with 8 g of whole oats and are foraged in by free-ranging meadow voles (Microtus pennsylvanicus). The difference in GUD between paired risky and safe trays provides an estimate of predation risk. Photo credit: Douglas Morris.


Photo 3. A risky open foraging tray with an automatic radio frequency identification (RFID) antenna attached to an event recorder. The recorder logs the entrance and departure times of all RFID-tagged rodents that forage in the tray. Total foraging time is a simple cumulation of the respective foraging intervals. Photo credit: Douglas Morris.


Photo 4. A closed safe foraging station with an automated RFID antenna (hidden from view under the cover) and its event recorder. Covers are suspended on small wooden supports to allow entry by voles. The supports are located parallel to the RFID antenna in order to eliminate false recordings of animals that might be resting or moving adjacent to the antenna, rather than foraging in the sand-filled tray. Photo credit: Douglas Morris.


Photo 5. Power and communication cables connect a series of electrical transformers and control units to eight data recorders (not in the photo) at the Lakehead University Habitron in northern Ontario, Canada. The middle platform serves as a field desk for a laptop computer used to download data on the identities and foraging activities of RFID-tagged meadow voles. Photo credit: Douglas Morris.

These photographs illustrate the article “Time-averaging voles match density with long-term habitat quality” by Douglas W. Morris published in Ecology.