Life History of the Kangaroo Rat Part 4

October 17, 1919. In good gra.s.s, but mound overrun by a large _Apodanthera_ vine.

Species stored. Per cent. Grams.

Aristida divaricata 90 to 95 } Chamaecrista leptadenia 10 to 5 } 58 Bouteloua rothrockii Tr. } Prosopis velutina 200 Apodanthera undulata 55 --- Total 313

Five species represented. Two species, _Apodanthera_, and _Chamaecrista leptadenia_, new to storage records. Several whole fruits of _Apodanthera_, about 2 inches in diameter, stored in addition to seeds alone; seeds of this form not previously noted in burrows, but very abundant in this one, indicating importance of the factor of accessibility in storage.

DEN 19.

October 31, November 1, 1919. In good gra.s.s. Entire burrow system mapped (Fig. 2, p. 29).

Species stored. Per cent. Grams.

Aristida spp. (probably mostly _divaricata_) 98 } Eriogonum sp Tr. } Bouteloua rothrockii 1 } 1,813 Bouteloua aristidoides 1 } Panic.u.m sp Tr. } Prosopis velutina 1,213 ----- Total 3,026

Five species represented, in addition to those of _Aristida_. Largest storage of _Prosopis_ found. Mound was near a good-sized mesquite tree.

No storage in subsidiary burrows.

DEN 21.

January 31, 1920. Male trapped here night of January 29, and suckling female trapped at same place and same opening of mound, night of January 30. Burrow excavated to secure young, which were found in special nest chamber.

Species stored. Grams.

Aristida spp. (intimate mixture of undetermined species) 1,115 Eschscholtzia mexicana (from spring of 1919) 48 Opuntia (p.r.i.c.kly pear, seeds only, no fruits) 10 ----- Total 1,173

Three species represented. p.r.i.c.kly pear hitherto found as fruits only.

DEN 22.

January 1, 1921. Rather good gra.s.s growth here in summer of 1920. Burrow typical, sandy soil. Two skulls of former residents unearthed.

Species stored. Grams.

Aplopappus gracilis (some B. rothrockii) 1,030 Astragalus nuttallia.n.u.s 630 Bouteloua rothrockii (some A. gracilis) 530 Sida diffusa 30 Solanum elaeagnifolium (282 fruits) 53 Loeflingia pusilla Tr.

Bouteloua aristidoides Tr.

Plantago ignota Tr.

Lupinus sparsiflorus Tr.

Old storage (mostly Bouteloua aristidoides with traces of B.

rothrockii and Aristida divaricata) 60 ----- Total 2,333

Eleven species represented. First instance of quant.i.ty storage of _Aplopappus gracilis_. First occurrence of _Loeflingia pusilla_ and _Astragalus nuttallia.n.u.s_.

DEN 24.

November 8, 1921. On mesa northeast of Albuquerque, N. Mex., near base of Sandia Mountains. Fair gra.s.s growth here during preceding summer.

Species stored. Grams.

Sporobolus cryptandrus strictus 5,455 Salsola pestifer 295 ----- Total 5,750

Two species represented. The heads of _Sporobolus cryptandrus strictus_ are retained to a great extent within the leaf sheaths. This necessitates the cutting of the stems into suitable lengths for carrying, and the stored material appears to be merely cut sections of the stems. Close examination, however, discloses the heads within, and shows that as in other instances seed storage is the end sought. These pieces are packed beautifully parallel like so many matches, and vary from a minimum length of 20 to a maximum of 37 millimeters, averaging about 30. Count of 2 grams of the above _Sporobolus_ material shows that there are 125 separate cut sections per gram, or a total of approximately 680,000 pieces in this one lot of storage, indicating a remarkable activity on the part of the individual rat (Pl. VIII, Fig.

1).

[Ill.u.s.tration: PLATE VII. FIG. 1.--DEN EXCAVATED ON RANGE RESERVE.

Vertical section through Den No. 1, of Table 1 (p. 20), showing the complex system of burrows, some of them plugged with closely packed storage (outlined in white), the depth of the den, and the widened chambers centrally located.]

[Ill.u.s.tration: PLATE VII. FIG. 2.--CONTENT OF EXCAVATED DEN.

Storage content of Den No. 1 (Fig. 1, above), showing the separate species of plants listed in Table 1. The rod is 1 meter long. The large pile on the left is composed of seed-laden heads of crowfoot grama (_Bouteloua rothrockii_), the large pile on the right consists of heads of six-weeks grama (_Bouteloua aristidoides_), the pile of heads in the center is desert plantain (_Plantago ignota_), and the smallest heap is composed of buckwheat-bush seeds (_Eriogonum polycladon_).]

The number of lots of storage (24) studied in detail, extending as it does over a period of three years with seasons of varying growth conditions, is not sufficient to permit the construction of a curve showing increase and decrease in quant.i.ty of stored material with growing seasons and intervals between; but the results indicate a very decided increase during the autumn storing season, and continuing large well into the winter, since some outside material can still be obtained until midwinter. From about February to April a decrease may be noted, followed, if the spring growth of annuals be good, by a slight increase; and we can very nearly predict the general character of the increases and decreases by the precipitation and consequent growth conditions.

TABLE 2.--_Quant.i.ty of storage per den correlated with time of year and growth conditions of preceding season (chiefly from United States Range Reserve near the Santa Rita Mountains, Ariz.)._

------------+-----------+-----------+----------- Den No. Date. Quant.i.ty. Preceding season.

------------+-----------+-----------+----------- 1918. _Grams._ 1 Feb. 7 4,127 Good.

2 Mar. 9 3,615 Do.

3 July 25 401 Poor.

4 Sept. 20 734 Do.

5 Sept. 21 2,520 Do.

6 Oct. 17 2,315 Do.

7 Dec. 20 1,247 Do.

1919. 8 Feb. 7 1,600 Do.

9 Mar. 13 370 Do.

10 Apr. 7 180 Do.[3]

11 Apr. 9 117 Good.[3]

12 May 7 298 Do.[3]

13 May 11 1,590 Do.

14 Aug. 8 5 Good.

15 Sept. 4 151 Do.

16 Oct. 17 313 Do.

17 Oct. 18 583 Do.

18 Oct. 25 3,410 Do.

19 Nov. 1 3,026 Do.

20 Dec. 13 2,816 Do.

1920. 21 Jan. 31 1,173 Do.

1921. 22 Jan. 1 2,333 Fair.

23[4] Nov. 7 1,685 Good.

24[4] Nov. 8 5,750 Do.