Remodeling Fever – Kangaroo Rat’s Reshape Burrow Systems Seasonally
27 May 2011 Filed in: Rodentia | Heteromyidae
Visit any home improvement store this time of year and you will see dozens of people purchasing materials to remodel or beautify their homes. We are not alone - banner-tailed kangaroo rats (Dipodomys spectabilis) also remodel their burrow systems every year (Figure 1).
Figure 1 A photo of the related giant kangaroo rat (Dipodomys ingens) at its burrow entrance (courtesy of J. Roser)
Burrows provide a number of important services for small mammals. These services include protection from predators, reduced thermoregulatory costs, storage sites for food caches, nurseries for rearing young, and hibernacula (in some species). Burrow systems also vary widely in architecture; the depth, number of side tunnels or chambers, and number of entrance/exits show considerable variation within a species. Is there an optimal architecture that would provide greater predator protection or reduce thermoregulatory costs? How does burrow architecture change with season?
These are some of the questions asked by Andrew Edelman in his 3-year study of burrow architecture in banner-tailed kangaroo rats (Edelman, 2011). Edelman hypothesized that kangaroo rats would modify the number of entrance/exits to burrow in response to ambient temperatures and predation pressure.
Banner-tailed kangaroo rats construct elaborate burrow systems with a surface mound containing multiple entrance/exit holes. These mounds can reach 4 meters across and are aggressively defended by their tenants. The burrows provide a refuge from temperature extremes, which is important for such desert dwelling species. They also provide protection from rattlesnakes, which are one of the few predators that can enter the burrows. Finally, kangaroo rats use chambers within the burrow system to larder hoard seeds. Consequently, burrows provide many functions, but what’s best for keeping seed stores edible may not be best for reducing thermoregulatory costs or providing protection from rattlesnakes. For example, the best protection from snakes would come from increasing the number of burrow exits, but in the winter many exits leads to cooler burrow temperatures and increased thermoregulatory costs for the resident kangaroo rat.
One solution is to modify the number of entrance/exits each season. That’s just what banner-tailed kangaroo rats do (Figure 2).
Figure 2. A graph of the mean number of burrow entrances (solid line) in banner-tailed kangaroo rat mounds and (b) mean surface air temperature, and (c) total precipitation from Mar. 2005 to Feb. 2008. (From Edelman, 2011)
Edelman found that the kangaroo rats plugged many entrance/exits during the winter months when ambient temperatures fell and when predation from rattlesnakes was at a minimum (rattlesnakes are dormant in winter at this study site). This strategy kept burrow temperatures warmer, potentially reducing metabolic heat loss for the resident rat. In contrast, during the summer months the number of entrance/exits on the mound increased. At this time of year western diamondback rattlesnakes are actively hunting and more exits means increased chances of survival for prey. Indirect support for this idea comes from the fact that females with litters had more burrow openings than males. Additionally, summers tend to be warmer and wetter, so increasing the number of surface openings increases ventilation within the burrow system, which reduces fungal growth and germination rates of seed caches.
Thus it appears that banner-tailed kangaroo rats remodel their burrow systems each spring and fall to optimize their fitness.
References
Edelman, A. (2011). Kangaroo Rats Remodel Burrows in Response to Seasonal Changes in Environmental Conditions Ethology, 117 (5), 430-439 DOI: 10.1111/j.1439-0310.2011.01890.x
Figure 1 A photo of the related giant kangaroo rat (Dipodomys ingens) at its burrow entrance (courtesy of J. Roser)
Burrows provide a number of important services for small mammals. These services include protection from predators, reduced thermoregulatory costs, storage sites for food caches, nurseries for rearing young, and hibernacula (in some species). Burrow systems also vary widely in architecture; the depth, number of side tunnels or chambers, and number of entrance/exits show considerable variation within a species. Is there an optimal architecture that would provide greater predator protection or reduce thermoregulatory costs? How does burrow architecture change with season?
These are some of the questions asked by Andrew Edelman in his 3-year study of burrow architecture in banner-tailed kangaroo rats (Edelman, 2011). Edelman hypothesized that kangaroo rats would modify the number of entrance/exits to burrow in response to ambient temperatures and predation pressure.
Banner-tailed kangaroo rats construct elaborate burrow systems with a surface mound containing multiple entrance/exit holes. These mounds can reach 4 meters across and are aggressively defended by their tenants. The burrows provide a refuge from temperature extremes, which is important for such desert dwelling species. They also provide protection from rattlesnakes, which are one of the few predators that can enter the burrows. Finally, kangaroo rats use chambers within the burrow system to larder hoard seeds. Consequently, burrows provide many functions, but what’s best for keeping seed stores edible may not be best for reducing thermoregulatory costs or providing protection from rattlesnakes. For example, the best protection from snakes would come from increasing the number of burrow exits, but in the winter many exits leads to cooler burrow temperatures and increased thermoregulatory costs for the resident kangaroo rat.
One solution is to modify the number of entrance/exits each season. That’s just what banner-tailed kangaroo rats do (Figure 2).
Figure 2. A graph of the mean number of burrow entrances (solid line) in banner-tailed kangaroo rat mounds and (b) mean surface air temperature, and (c) total precipitation from Mar. 2005 to Feb. 2008. (From Edelman, 2011)
Edelman found that the kangaroo rats plugged many entrance/exits during the winter months when ambient temperatures fell and when predation from rattlesnakes was at a minimum (rattlesnakes are dormant in winter at this study site). This strategy kept burrow temperatures warmer, potentially reducing metabolic heat loss for the resident rat. In contrast, during the summer months the number of entrance/exits on the mound increased. At this time of year western diamondback rattlesnakes are actively hunting and more exits means increased chances of survival for prey. Indirect support for this idea comes from the fact that females with litters had more burrow openings than males. Additionally, summers tend to be warmer and wetter, so increasing the number of surface openings increases ventilation within the burrow system, which reduces fungal growth and germination rates of seed caches.
Thus it appears that banner-tailed kangaroo rats remodel their burrow systems each spring and fall to optimize their fitness.
References
Edelman, A. (2011). Kangaroo Rats Remodel Burrows in Response to Seasonal Changes in Environmental Conditions Ethology, 117 (5), 430-439 DOI: 10.1111/j.1439-0310.2011.01890.x