Reproductive timing and reliance on hoarded capital resources by lactating red squirrels

Quinn E. Fletcher, Manuelle Landry-Cuerrier, Stan Boutin, Andrew G. McAdam, John R. Speakman, Murray M. Humphries

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43 Citations (Scopus)


Successful reproduction in a seasonal environment can be accomplished with resources that are stored before use ("capital resources") or resources that are used immediately ("income resources"). Research examining capital versus income resource usage during reproduction has primarily focused on assigning species to positions along a capital-income gradient. Here, we examine the causes and reproductive consequences of among and within-year variation in hoarded capital versus income resource usage by female North American red squirrels (Tamiasciurus hudsonicus) during mid-lactation in a highly seasonal environment. Among years, the proportion of feeding events that were on capital resources (PROPCAP) averaged 39 % during the yearly median mid-lactation periods, but ranged widely between 2 and 100 %. In years with earlier parturition dates, females primarily used hoarded capital resources during mid-lactation, whereas in years with later parturition dates, females primarily used income resources during mid-lactation. Within years, PROPCAP during mid-lactation tended to be greater in early-breeding females than in late-breeding females. Rates of water flux in females during mid-lactation provided further evidence that late-breeding females used more water-rich income resources. The proportion of litters that were partially or completely lost, and the litter mass that lactating females supported, was not influenced by the large among-year differences in hoarded capital resource usage. Red squirrels appear to delay reproduction following years with low cone production to time peak reproductive demands to be late enough to be supported by income resources that only become available later in the season. In conclusion, our results offer a rare example of the capacity of a food-hoarding mammal to support reproduction exploiting a wide range of capital and income resources.

Original languageEnglish
Pages (from-to)1203-1215
Number of pages13
Issue number4
Early online date3 Jul 2013
Publication statusPublished - Dec 2013

Bibliographical note

We thank all squirrelers, especially Maura Forest for her field data collection and initial work on this project. We are grateful to Ainsley Sykes and Elizabeth Anderson for their assistance with field data preparation. Thanks also to Paula Redman and Peter Thomson for technical assistance in isotope analyses for the DLW work. We thank the Champagne and Aishihik First Nations for allowing us to do research on their lands. We thank Agnes Moose and her family for access to her traditional trapping area. Research support was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC), the National Science Foundation (Grant DEB-0515973), and Northern Scientific Training Program Grants to S.B., A.G.M. and M.M.H., and Q.E.F. An NSERC Postgraduate Graduate Scholarship provided personal support to Q.E.F. This is paper number 70 of the Kluane Red Squirrel Project.


  • Capital and income breeding
  • Diet
  • Phenology
  • Reproductive timing
  • Seasonal environments


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