A Giant among Kangaroo Rats

Can you see it? It's a crappy image, but it's good enough . . . 

When you're squinting at your camera trap images on the LCD in the glaring sun it's easy to miss the little guys, even if they're giants among their kind.

So the thrill of seeing a new species in the latest Chimineas survey was delayed until the jpegs were uploaded to computer.

Mind you, I can't swear that  the small blobular creature on the right is Dipodomys ingens, but compared with other photos I have a strong hunch it's the real thing.

Among kangaroo rats, Dipodomys ingens is a giant, with larger males weighing in at as much as 140 g (= 0.3 lb) when they are bulked out in the month of August.

Equally appropriate names would be the big-footed or big-headed kangaroo rat because the head and hindfeet are oversized compared to most other kangaroo rats.

We knew ingens was on the ranch because their skulls litter the ground beneath the winter roosts of the long-eared owls.

It was a welcome addition to our mammalian species list.

Craig photographed it in annual grassland.

The lovely big-eyed rat probably had a patchy distribution even before Father Junipero Serra and his followers drove cattle up el Camino Real and scattered Mediterranean weeds across the western plains of the San Joaquin valley.

When Joseph Grinnell was digging up k-rat burrows in the early '30s ingens colonies were spread across thousands of acres of rangeland.

Wherever Grinnell and his contemporaries found ingens, it reigned supreme over other rodents, "--it 'owns' whole square miles to the practical exclusion of other seed-eating rodents."

Even California ground squirrels were largely absent in giant kangaroo rat country.

This is puzzling because kangaroo rats and ground squirrels work different time shifts, and ecological theory predicts this difference should at least reduce competition when resources aren't severely limited.

The State Water Project of the '60s and '70s changed the situation by irrigating the western part of the Tulare Basin, which fragmented the saltbush community and converted most of it agroscape.

The k-rat disappeared over a large segment of its former range, and in the 1980s the State of California and US Fish and Wildlife Service listed the giant kangaroo rat as endangered.

The Carrizo Plain remains a giant kangaroo rat stronghold, but a strange thing has happened there: the rat has formed an unsavory alliance with alien weeds from the Mediterranean.

The k-rat likes the big seeds of five annual weeds, and two of them, redsteam filaree (Erodium cicutarium) and foxtail brome (Bromus madritensis) thrive and dominate the flora in the rats' precincts, the most active parts of their home ranges.

The k-rats gather and cache the seeds in granaries, and when it rains some of them sprout in the disturbed soil, which the k-rats prepare and till by nightly digging, burrowing, dust-bathing, and plant clipping activities.

An endangered kangaroo rat that cultivates undesirable exotic weeds is a Catch-22 for conservation biologists.

You may not be able to eradicate the weeds and restore the grassland without threatening the k-rat -- and if you hasten the k-rat's recovery you'll spread the exotic weeds.

This may be a case where you can't have it both ways.

Save the giant k-rat and the weeds are here to stay.

References
Grinnell, J. 1932. Habitat relations of the giant kangaroo rat. Journal of Mammalogy 13:305-20.

Schiffman, P. 1994. Promotion of exotic weed establishment by endangered giant kangaroo rats (Dipodomys ingens) in a California grassland.  Journal Biodiversity and Conservation. 3(6):1572-9710.

Williams, D.F. and K.S. Kilburn. 1991. Dipodomys ingens. Mammalian Species No 377:1-7.

Williams, D.F., M.K. Davis and L. P. Hamilton. 19 95.  Distribution, population size, and habitat features of giant kangaroo rats in the northern segment of their geographic range. Bird and Mammal Conservation Program Report  95-01, State of California Department of Fish and Game, 44 pp.