Effects of Acorn Production on White-Footed Mouse Populations

• Investigators: Rebecca Field, Catherine Langtimm, John O'Keefe
• Contact: Catherine Langtimm
• Start date: 1997-01-01
• End date: 1999-12-31
• Location: Harvard Forest
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• Longitude:
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• Taxa: Peromyscus leucopus (white-footed mouse)
• Keywords: acorns, mast production, mice
• Abstract:

  Recently several authors have documented fluctuations in the abundance of white-footed mice (Peromyscus leucopus noveboracensis) with fluctuations in acorn production (Elkinton et al. 1996, Ostfeld et al. 1996, Wolff 1996, Jones et al. 1998). Acorns are the major food source of white-footed mice during winter and are extensively cached. They are also food for many other species as well; over 100 species of birds and mammals feed on acorns (Van Dersal 1940). A large mast crop in fall usually correlates with a large mouse population the following summer, whereas a poor crop correlates with low population numbers. One experimental study supplementing acorns on forest plots demonstrated a concomitant increase in white-footed mice populations (Jones et al. 1998). It has been hypothesized that a large mast crop increases overwinter survival and may allow continued reproduction during the winter months, which results in a larger population the following year.

  We have four objectives in monitoring acorn abundance at Harvard Forest: 1) test for correlation of estimates of acorn production with estimates of overwinter survival probabilities and abundance of white-footed mice using mark-recapture statistical models (HF054), 2) document annual variation in acorn abundance and quality, which compliments a program at Harvard Forest documenting changes in woody plant phenology with climatic variation (HF003), 3) test hypotheses concerning the correlation of acorn production with environmental factors such as temperature, rainfall, and weevil infestation, and 4) provide data for inter-site comparisons, such as to test for synchrony in production at various scales across the landscape.

  We estimate acorn production with timed visual surveys following methods adapted from Koenig et al. (1994). Individual tagged trees on two small mammal trapping plots are surveyed each year by two observers. Detailed methods are described in the metadata.

• Methods:

  Visual surveys of acorns in the crown of individually tagged oak trees are made each year in late summer. Methods were modified from Koenig, W. A. et al. 1994. Estimating acorn crops using visual surveys. Canadian Journal of Forestry Research 24:2105-2112. The nearest dominant or co-dominant oak tree at each station on the small mammal trapping grid is surveyed by two observers scanning the crown with binoculars. Each observer takes turns systematically scans the crown, counting out loud the number of acorns seen. A recorder with a stop watch records the total count at 15, 20, 25, and 30 seconds. After the count each observer classifies the crop into one of five general conditions and comments on the number of acorns on the ground under the tree.

• Related datasets: HF003 HF054