Hispid cotton rat facts for kids
Quick facts for kids Hispid cotton rat |
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| Conservation status | |
| Scientific classification | |
| Genus: |
Sigmodon
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| Species: |
hispidus
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The hispid cotton rat (Sigmodon hispidus) is a type of rodent. For a long time, people thought this species lived in many parts of South America, Central America, and southern North America.
But new studies, looking at their mitochondrial DNA, have shown that this one widely spread species is actually three different ones. These are S. hispidus, S. toltecus, and S. hirsutus.
The S. hispidus cotton rat lives from Arizona in the west to Virginia in the east. Its range goes from the Platte River in Nebraska in the north, likely down to the Rio Grande in the south. This is where its home meets the area of the S. toltecus.
Adult hispid cotton rats are usually about 20 to 34 centimeters (8 to 13 inches) long. Their tail is about 9 to 12 centimeters (3.5 to 5 inches) long. They weigh between 50 and 250 grams (1.8 to 8.8 ounces). These rats have even been used in laboratories for scientific studies.
Contents
What's in a Name? (Taxonomy)
The official scientific name for the hispid cotton rat is Sigmodon hispidus. It belongs to a group of rodents called the Cricetidae family.
Scientists recognize about 25 different types, or subspecies, of the hispid cotton rat. However, genetic studies show there are two main groups within the species. One group lives in the eastern part of their range, and the other lives in the western part. These two groups can mix where their areas meet.
Where Do They Live? (Distribution)
In the United States, the hispid cotton rat lives in many states. You can find them from southern Virginia and North Carolina, west through Tennessee, and up to northern Missouri. They also live in Kansas, southern Nebraska, southeastern Colorado, New Mexico, and southeastern Arizona. Their range extends south to the Gulf Coast and into northern Mexico.
They are not found in the coastal plain of North Carolina or in the mountains of Virginia. Some smaller groups live separately in southeastern Arizona and extreme southeastern California, reaching into Baja California Norte. In Kansas, these rats have only appeared in the last 50 years.
Their Home (Habitat)
Hispid cotton rats live in many different kinds of places. However, they don't just live anywhere. They really like areas with lots of grass and some shrubs. They don't seem to prefer areas with many broad-leafed plants (dicots).
How they use and prefer their habitat often depends on how much grass is around. But some studies show that other plants can be important too. For example, they might like areas with many dicots if there's still good plant cover. In Kansas, their numbers grew in areas where prairie land was plowed. This led to more types of early plants growing.
Male hispid cotton rats are less picky about where they live than females. In Texas, males were found in grassy, shrubby, and mixed areas about equally. Females, however, tended to choose mixed habitats more often.
Their habitat choices also change with the seasons and if they are breeding. In Texas, they preferred grassy areas with some shrubs in spring. In the fall, they liked areas with more shrubby cover.
In Kansas prairies, hispid cotton rats prefer dense undergrowth. They also like areas with protective plants like big bluestem. They are often found in grassy clearings, farm fields, overgrown areas, and along roadsides. They are common in ungrazed uplands and sandy mixed-grass prairies. They also like disturbed areas, which helped them spread into north-central Kansas.
In Texas rangelands, their numbers increased where there was more plant growth. This included plants they could eat, like bristlegrasses. Rat numbers were four times higher in areas planted with certain foreign grasses. These included King Ranch bluestem and buffel grass.
In northeastern Kansas, hispid cotton rats had high numbers in tallgrass prairies. But their numbers dropped as these areas changed into brush and trees over 28 years. They are sometimes found in areas with early-growing grassland plants.
Hispid cotton rats live in grassy or early-growth areas within open woods. In the Southeast, their numbers increase with plants like broomsedge. But their numbers go down as the area changes into brush and trees. In Texas pine-hardwood forests, they were often caught in narrow areas along streams. These areas have more light and ground cover.
In Louisiana, they were found in pine stands with surface cover. They were not found in dense, pole-sized timber. This is because pole-sized timber blocks light and has little ground cover. In Louisiana and Mississippi, they were more common in cut bottomland forests than in uncut ones. They were also more common in cottonwood tree farms. In northern Georgia, clearing pine-hardwood forests helped more food plants grow. This led to more small mammals, including cotton rats.
In Colorado, hispid cotton rats live in damp areas with many grasses and weeds. They seem to prefer warmer places. In New Mexico, they usually don't live where the average yearly temperature is below 13°C (55°F). They also avoid places where the growing season is shorter than 180 days. In Trans-Pecos, Texas, they live at warmer, low elevations with moderate to dense grass cover.
When water is added to certain swampy areas, hispid cotton rats move to drier spots. Rising water levels favor marsh rice rats over cotton rats.
Scientists have studied how many hispid cotton rats live in an area. The average number is about 5 to 31 rats per hectare (about 2 to 12 rats per acre). In Texas, numbers varied from 1 to 84 rats per hectare depending on the habitat. In Florida, numbers ranged from 0 to 94 rats per hectare. In Kansas, the highest number was 65 rats per hectare in their favorite habitat.
In one study, hispid cotton rats preferred only the largest patches of grass. These patches were 50 by 100 meters (165 by 330 feet). They were less common in medium-sized patches. They were very rare in the smallest patches.
In Kansas, an adult male cotton rat's home range was about 0.39 hectares (0.969 acres). For adult females, it was about 0.22 hectares (0.543 acres). The farthest a male traveled was 100 meters (330 feet). For a female, it was 76 meters (250.9 feet). In Texas, males also had larger home ranges than females. Home ranges were bigger in summer and winter than in spring and fall.
The size of their home range was related to their body weight. It was smaller when there were more rats in the area. They showed some dislike for other rats, especially of the same sex. In Texas, hispid cotton rats could find their way back home from far away. They were good at finding their way back from up to 300 meters (990 feet) away. This means they know the area well within that distance.
Cover Requirements
In the southern Coastal Plain, hispid cotton rats use burrows made by gopher tortoises. They use these burrows for shelter in sandy areas with pine and oak trees.
Plant Communities
Hispid cotton rats live in areas with mesquite trees in Arizona and New Mexico. In the Coastal Plain, they live near the edges of bald cypress swamps. They are also common in old rice fields in Texas, especially near overgrown canal banks.
In Florida, they are common in areas with sabal palm and coconut palm trees. In the Southeast, they prefer grassy areas under pine trees that are kept open by fires.
Sometimes, hispid cotton rats move into sand pine scrub areas for short times. This might happen when there are many rats in nearby good habitats. Sand pine scrub has little ground cover, so it's not their favorite place to live.
Life and Habits (Behavior and Biology)
Hispid cotton rats are mostly active at night. But they can be seen at any time of day. Their activity depends on things like weather and other animals. They are active all year long.
They usually have two main breeding seasons. Most babies are born in late spring and again in late summer or early fall. In some areas, they breed in March and June. Females were found to be pregnant from March through July. They do not breed in the coldest winter months. In Kansas, they only breed when there is no frost.
The female builds a nest on the ground or in a burrow. Nests are shaped like a cup or a ball and are made of woven grasses. Cotton rats in colder northern areas make thicker nests than those in the south.
Pregnancy in hispid cotton rats lasts about 27 days. A female can have from one to 15 babies at a time. Larger litters are more common in northern areas and later in the season. Newborns are quite developed. They can move and have light fur, but their eyes are not open yet. Their eyes open about 18 to 36 hours after birth. They stop drinking milk from their mother in 10 to 15 days. They reach adult size by about 41 days old.
Some male cotton rats can have babies by 60 days old. Some females can get pregnant by 30 to 40 days old. The earliest a female was recorded pregnant was at 38 days. These rats are known for having many babies in the Southeast. Females can have two or more litters each year. This depends on where they live and the local weather. Females can mate again within 24 hours of giving birth.
Hispid cotton rat groups usually stay in one place. Their numbers depend mostly on how many babies are being born. In Kansas, their numbers were highest in fall and early winter. They were lowest in spring and early summer. In the northern parts of their range, bad weather can cause their numbers to drop quickly. In Kansas, many rats died in severe weather in March and April.
In many areas, their numbers can drop to zero, meaning they disappear from that spot. In Georgia, their numbers were lowest after droughts and very cold winters. These drops in numbers were linked to less plant growth and cover.
In Georgia, if there were more than 15 rats per acre, many of them died. This was often due to predators. If there were fewer than 15 rats per acre, fewer died from predators. When many different kinds of predators are around, they are more important than food or weather in limiting cotton rat numbers.
In another study in Georgia, fields were covered with nets to protect rats from birds. This cover did not affect how many new rats joined the group in spring and summer. But it greatly reduced deaths in autumn and winter. This suggests that birds are more important predators than mammals. Also, in winter, many rats die from predators. But in breeding seasons, rats can make up for losses by having more babies.
What Do They Eat? (Diet)
Hispid cotton rats eat many different things, but mostly green plants. They sometimes eat insects and other small animals. They prefer to eat the stems, leaves, and seeds of both farm plants and wild plants.
In the Southeast, they eat a lot of perennial legumes and broomsedge. They also eat roots and tubers. In Texas, their diet always included the lower green stems of grasses. They also ate raspberries, privet fruits, and fogfruit leaves when available.
Who Eats Them? (Predators)
Many animals hunt and eat hispid cotton rats. These include birds, reptiles, and other mammals.
In Oklahoma, Swainson's hawks often eat hispid cotton rats. In central Missouri, cotton rats made up 19% of the food found in red-tailed hawk nests. Their remains were also a big part of short-eared owl pellets in Arkansas.
Hispid cotton rats were the third most important food for red wolves in eastern Texas and Louisiana. In North Carolina, bobcats ate many hispid cotton rats. They were a smaller part of the diet of Florida panthers.
In north-central Florida, scientists saw a corn snake killing a hispid cotton rat. The snake was waiting where a trap had been set.
