Flying squirrels use a mortise-tenon structure to fix nuts on understory twigs
- Research Institute of Tropical Forestry, Chinese Academy of Forestry, China
- College of Forestry, Hainan University, China
- Department of Renewable Resources, University of Alberta, Canada
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, China
Figures
Figure 1
Spatial distribution of the 151 suspended nuts observed in Jianfengling Nature Reserve, Hainan, China.
Figure 2
Nuts are stored after surface preparation by flying squirrels.
(A) Nut of C. edithiae (Skan) Schottky, with chewed grooves outlined in red. Nuts of C. edithiae fixed on trees, with (B–D) one groove, (E) two non-connected grooves, or (F) spiral carved grooves encircling the nuts. (G) Nut of C. patelliformis (Chun) Y. C. Hsu et H. W. Jen, with chewed grooves outlined in red. (H–I). Nuts of C. patelliformis fixed on trees, with carved grooves on the bottom fixed on (J) bamboos, (K–L) lianas, between the big petioles of (M) trees and (N) palms.
Figure 3
Variation in carved grooves depends on the storage situation.
The carved surface grooves on nuts of C. edithiae mostly encircle the middle of the nut, with (A) one groove, (B) one spiral groove, or (C) two separated grooves. The grooves on nuts of C. patelliformis are distributed on the bottom of the nuts, with (D) 2, (E) 4, (F) 6, (G) 8, (H) 10 symmetrically, or (I) randomly distributed grooves.
Figure 4
Nuts were fixed tightly between twigs generally meeting at angles of 25–40°.
(A) C. edithiae nuts. (B) C. patelliformis nuts.
Figure 5
Most nuts were stored on small plants with the diameter at breast height (DBH) ranging from 0.4–1.6 cm.
(A) C. edithiae nuts. (B) C. patelliformis nuts. Notes: The value on each bar is the actual number of stored nuts.
Figure 6
Nuts were stored mainly on small plants between twigs with diameters of 0.10 - 0.60 cm.
(A) Histogram of diameters of twigs used to store nuts of C. edithiae. (B) Histogram of diameters of twigs used to store nuts of C. patelliformis. Notes: The value on each bar is the actual twigs with the number of stored nuts.
Figure 7
Grooves carved by squirrels on most C. edithiae nuts were 0.2 - 0.6 cm in width.
Figure 8
Nuts were generally stored on the first to third branches at 1.5–2.5 m aboveground.
(A) C. edithiae nuts. (B) C. patelliformis nuts. Notes: The value on each bar is the actual number of stored nuts.
Figure 9
Number of grooves carved on the oblate nuts of C. patelliformis.
(A) Most nuts had fewer than eight grooves. (B) The depth of most grooves was shallow to medium. Notes: The value on each bar is the actual number of stored nuts.
Figure 10
Distance from storage sites to potential parent trees for the nuts varied from 10–25 m.
(A) C. edithiae nuts. (B) C. patelliformis nuts. Notes: The value on each bar is the actual number of stored nuts.
Figure 11
After long (e.g. >ca. 365 days) storage, nuts become not fresh.
(A) Dried nuts, (B) Germinated, or (C–E) Destroyed by insects.
Videos
Video 1
Squirrel 1 of Hylopetes alboniger was checking and re-fixing nuts at the storage sites with footage from infrared cameras.
Video 2
Squirrel 2 of Hylopetes alboniger was removing nuts from storage sites with footage from infrared cameras.
Video 3
Squirrel 3 of Hylopetes alboniger was removing nuts from storage sites with footage from infrared cameras.
Video 4
Squirrel 4 of Hylopetes phayrei electili was checking and re-fixing nuts at storage sites with footage from infrared cameras.
Video 5
Squirrel 5 of Hylopetes phayrei electili was removing nuts from storage sites with footage from infrared cameras.
Video 6
One squirrel was cracking the nuts on the ground with footage from infrared cameras.
Video 7
One squirrel was rotating and cracking the nuts on the trees with footage from infrared cameras.
Video 8
One squirrel was re-fixing the nuts by cracking behavior with footage from infrared cameras.
Video 9
One squirrel was fixing the nuts between the twigs with footage from infrared cameras.
We merged several photos and a video successively taken by an infrared camera in 30 s.
Video 10
Footage of shaking a liana does not dislodge nuts of Cyclobalanopsis edithiae stored by squirrels.
Video 11
Footage of shaking a sapling does not dislodge nuts of Cyclobalanopsis edithiae stored by squirrels.
Video 12
Footage of shaking a sapling does not dislodge nuts of Cyclobalanopsis edithiae stored by squirrels.
Video 13
Footage of shaking a liana does not dislodge nuts of Cyclobalanopsis patelliformis stored by squirrels.
Video 14
Footage of shaking a sapling does not dislodge nuts of Cyclobalanopsis patelliformis stored by squirrels.
Video 15
Footage of shaking a sapling does not dislodge nuts of Cyclobalanopsis patelliformis stored by squirrels.
Tables
Table 1
The nine squirrel species known from Jianfengling, Hainan Island, China.
| Species and subspecies name | Body length/mm |
|---|---|
| Tamiops maritimus (Bonhote,1900) (Liu et al., 2020; Pan et al., 2007) | 105～134 |
| Dremomys pyrrhomerus (Thomas, 1895) (Xu and Chen, 1989) | 194～215 |
| Hylopetes alboniger (Hodgson, 1870) (Liu et al., 2020; Andrew, 2008; Pan et al., 2007) | 180～203 |
| Hylopetes phayrei electilis (Allen, 1925) (Liu et al., 2020; Pan et al., 2007) | 123～173 |
| Dremomys rufigenis (Blanford, 1878) (Zheng et al., 2008) | 170～250 |
| Callosciurus erythraeus (Pallas, 1779) (Huang, 1995; Zheng et al., 2008) | 198～252 |
| Belomys pearsonii (Gray, 1842) (Pan et al., 2007; Huang, 1995) | 180～260 |
| Petaurista albiventer (Gray, 1834) (Jing et al., 2007) | 420～520 |
| Ratufa bicolor (Sparrmann, 1778) (Li et al., 2008) | 350～505 |
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Note: The data in this table are referenced from the below literature.
Table 2
The types of plants used for nut storage.
| Plant type | Number of individuals | Percentage of all individuals (%) |
|---|---|---|
| Alive tree | 108 | 71.5 |
| Dead tree | 17 | 11.3 |
| Alive liana | 19 | 12.6 |
| Dead liana | 2 | 1.3 |
| Bamboo | 5 | 3.3 |
| Total | 151 | 100 |
Table 3
Main Fagaceae species found in a 60 ha plot in the Jianfengling forest.
| Species | Abundance |
|---|---|
| Castanopsis carlesii (Hemsley) Hayata | 3269 |
| Castanopsis fissa (Champion ex Bentham) Rehder & E. H. Wilson | 2803 |
| Castanopsis jianfenglingensis Duanmu | 2297 |
| Castanopsis tonkinensis Seemen | 953 |
| Castanopsis ledongensis C. C. Huang & Y. T. Chang | 335 |
| Castanopsis fabri Hance | 113 |
| Castanopsis hystrix J. D. Hooker & Thomson ex A. de Candolle | 35 |
| Cyclobalanopsis edithiae (Skan) Schottky | 1645 |
| Cyclobalanopsis patelliformis (Chun) Y. C. Hsu & H. W. Jen | 1207 |
| Cyclobalanopsis phanera (Chun) Y. C. Hsu & H. W. Jen | 886 |
| Cyclobalanopsis fleuryi (Hickel & A. Camus) Chun ex Q. F. Zheng | 568 |
| Cyclobalanopsis neglecta Schottky | 392 |
| Cyclobalanopsis blakei (Skan) Schottky | 279 |
| Cyclobalanopsis hui (Chun) Chun ex Y. C. Hsu & H. W. Jen | 220 |
| Lithocarpus longipedicellatus (Hickel & A. Camus) A. Camus | 2842 |
| Lithocarpus pseudovestitus A. Camus | 2427 |
| Lithocarpus fenzelianus A. Camus | 1751 |
| Lithocarpus amygdalifolius (Skan) Hayata | 1360 |
| Lithocarpus handelianus A. Camus | 1046 |
| Lithocarpus fenestratus (Roxburgh) Rehder | 323 |
| Lithocarpus howii Chun | 130 |
| Lithocarpus hancei (Benth.) Rehd. | 71 |
Additional files
-
MDAR checklist
- https://cdn.elifesciences.org/articles/84967/elife-84967-mdarchecklist1-v2.docx
-
Supplementary file 1
The plants used to store nuts and their growth form.
- https://cdn.elifesciences.org/articles/84967/elife-84967-supp1-v2.xlsx
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Flying squirrels use a mortise-tenon structure to fix nuts on understory twigs
eLife 12:e84967.
https://doi.org/10.7554/eLife.84967
