Time-concentrated sampling: a simple strategy for information gain at a novel, depleted patch

Abstract

When an animal has found and consumed food at a new location, information about whether and when food will be present again could improve future foraging efficiency. A series of rapid returns followed by less frequent visits and finally abandonment of the patch could provide such information. By analogy with area-concentrated (area-restricted) search, we call this hypothesized pattern “time-concentrated sampling”. We tested whether eastern chipmunks ( Tamias striatus (L., 1758)) would show time-concentrated sampling in the field and whether the pattern of visits would be affected by patch value. We used peanuts to induce animals to discover a small patch of sunflower seeds. After depleting the patch, returning to find it empty, and leaving without food, 36 of 40 animals returned on sampling visits. Sampling rate was initially high and declined over 4 h. The number of peanuts and number of visits where seeds were obtained positively predicted sampling rate, but the volume of sunflower seeds presented and the distance to the burrow did not. We conclude that chipmunks exhibit flexible time-concentrated sampling.

Resource tracking by eastern chipmunks: the sampling of renewing patches

“…The increasing rate of sampling over stage 1 in our experiment may be explained by a similar pattern. Chipmunks early in stage 1 may have shown the same pattern as those in the Gibson et al (2006) study, sampling frequently immediately after exploiting a renewal but then quickly decreasing their sampling frequency with time. If, like the starlings in Inman's study, chipmunks in our experiment showed more consistent sampling as they gained experience with patch renewal, then the average sampling rate would increase over time during stage 1.…”

“…In addition, least chipmunks and golden-mantled ground squirrels returned to a patch that they had last experienced as empty if their previous experience suggested that patch quality could change over time (Devenport and Devenport 1994). Two other recent studies from our group have also shown that eastern chipmunks will return to sample multiple times on the day they discover and deplete a small patch (Hall 2004;Gibson et al 2006). The present study extends previous work by showing that sampling rate will increase with experience of Fig.…”

“…Two previous studies have shown that animals foraging at one site will invest part of their time visiting alternative sites, as would be expected if animals were sampling (eastern chipmunks, Tamias striatus (L., 1758): Kramer and Weary 1991;great andblue tits, Parus caeruleus L., 1758: Naef-Daenzer 2000). A foraging study of least chipmunks (Tamias minimus Bachman, 1839) and golden-mantled ground squirrels (Spermophilus lateralis (Say, 1823)) showed that animals will return to a patch they had last experienced as empty (Devenport and Devenport 1994), and two other studies from our group have shown that eastern chipmunks will return repeatedly to a novel patch site within hours after depleting it (Hall 2004;Gibson et al 2006). These findings suggest that sampling is part of natural foraging behaviour, but there are no detailed observations on how free-ranging animals sample patches over time, nor on how closely they track patch variability.…”

“…This pattern disappeared as the birds gained experience with the feeder, presumably because they had gained confidence that the feeder would eventually switch back to good. Gibson et al (2006) proposed that sampling at a high rate soon after a patch is depleted and then decreasing the rate over time if no renewal is experienced would be an effective response to a novel patch with unknown characteristics. They showed that chipmunks followed this pattern over a period of several hours after they had exploited a single small, non-renewed patch.…”