Elsevier

Animal Behaviour

Volume 86, Issue 4, October 2013, Pages 783-789
Animal Behaviour

Foraging dynamics in Steller's jays: size and viability of cacheable food items

https://doi.org/10.1016/j.anbehav.2013.07.018Get rights and content

Highlights

  • •

    Steller's jays may handle several food items to evaluate size and storage viability.

  • •

    We measured population-level preferences for items and individual sampling behaviour.

  • •

    Jays chose heavier nuts with intact shells and sampled more when item quality varied.

  • •

    Jays that chose optimal cache items sampled more items than jays that chose poorly.

  • •

    Jays may evaluate cache items based on current and future expected energetic values.

Several species of birds and mammals cache food items, which in harsh conditions may translate into improved survival or reproductive success. Animals may benefit from evaluating the quality of cache items in terms of size, nutrition and storage viability. Steller's jays, Cyanocitta stelleri, which cache seeds for later consumption, may handle multiple food items with their beak prior to making a selection. By picking items up, individuals may use visual and tactile cues to evaluate size and shell condition. The number of items an individual jay handles is repeatable, reflecting consistent individual-specific foraging behaviours that may differentiate success at selecting high-quality cache items. In this study we quantified population-level preferences for food items based on size and shell integrity, and individual Steller's jay sampling behaviour when presented with these choices. Using field trials with free-ranging subjects, we quantified sampling frequency in a variety of choice tests and measured individuals' success at choosing higher-quality items. We found that Steller's jays selected items of greater weight and items with intact shells, and preferences for these properties were of comparable magnitude. Jays sampled more nuts during choice sets involving cracked and intact shells, resulting in individuals selecting more profitable nuts for caching. These results may suggest that Steller's jays evaluate cache items based on both current and future expected energetic values, and that sampling behaviour may enable them to choose more valuable forage items.

Section snippets

Methods

We studied foraging behaviour in free-ranging Steller's jays on the Humboldt State University campus and surrounding residential areas of Arcata, CA, U.S.A. (40°59′N, 124°06′W). The study area was 2.2 km2, bordered to the east by forest dominated by California redwood (Sequoia sempervirens). Steller's jays cache items year round for short- and long-term storage, to be retrieved and consumed at a later time (Greene et al. 1998). They are a useful species for behavioural studies, as they are

Item Preference and Selectivity

Sixty adult, territorial Steller's jays (34 males and 26 females) were tested in baseline foraging trials and four sets of choice tests. Only 52 of these birds participated in the large versus medium choice test. Of visits in which a single nut was taken (90.8% of all visits), birds selected medium (double-chambered) nuts over small (single-chambered) nuts at a ratio of 10.3 to 1 (chi-square test: χ12=198.5, N = 295, P < 0.001; Fig. 1a). Birds chose large nuts over medium nuts (2.5:1; χ12=52.5, N = 

Discussion

Steller's jays expressed noticeable preferences for larger nuts and those that were structurally intact. Selection was strongest when items were easily distinguishable (one-chambered versus two-chambered nuts). This is reasonable given that animals seem to perceive relative differences in size (Langen and Gibson, 1998, O'Brien et al., 2005). The medium peanuts were 50% larger than the small, whereas the large peanuts were only 25% larger than the medium. Similar size and weight preferences have

Acknowledgments

We thank Jeff Jacobsen, Jeffrey Zirpoli, Anthony Desch and members of the J. M. Black laboratory for their assistance and input. We appreciated commentary on the manuscript from two anonymous referees. We are grateful for the cooperation of Arcata landowners for their interest and participation in the long-term Steller's jay study. Funding was provided by the Stanley and Lorene Harris Scholarship Fund and Humboldt State University's Sponsored Programs Foundation.

References (38)

  • H. Zhang et al.

    Differences of dispersal fitness of large and small acorns of Liaodong oak (Quercus liaotungensis) before and after seed caching by small rodents in a warm temperate forest, China

    Forest Ecology and Management

    (2008)
  • I. Bossema

    Jays and oaks: an eco-ethological study of a symbiosis

    Behaviour

    (1979)
  • J.L. Brown

    Aggressiveness, dominance and social organization in the Steller jay

    Condor

    (1963)
  • N.J. Dingemanse et al.

    Natural selection and animal personality

    Behaviour

    (2005)
  • N.J. Dingemanse et al.

    Fitness consequences of avian personalities in a fluctuating environment

    Proceedings of the Royal Society B

    (2004)
  • M.D. Dixon et al.

    Effects of weevil larvae on acorn use by blue jays

    Oecologia

    (1997)
  • C.L. Frank

    The effects of moldiness level on seed selection by Dipodomys spectabilis

    Journal of Mammalogy

    (1988)
  • P.O. Gabriel et al.

    Behavioural syndromes, partner compatibility and reproductive performance in Steller's jays

    Ethology

    (2012)
  • R.P. Gendron et al.

    Food perishability and inventory management: a comparison of three caching strategies

    American Naturalist

    (1995)

    • Cited by (0)

    1

    E-mail address: [email protected] (P. O. Gabriel).

    2

    E-mail address: [email protected] (J. M. Black).

    View full text
    Copyright © 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.