Flora and Fauna

Big Brown Bat

Little Brown Bat

Bats (wetland) - Bats are crepuscular mammals (active at dawn or dusk), which make up 20 percent of all mammalian species. At Bluff Lake we have two different species, the Big Brown Bat, and the Little Brown Bat. These species are most common in urban environments because they have the ability to roost in many different locations. These species are insectivores whose diet consists of moths, wasps, mosquitoes, gnats, midges and other insects. Bats play an important role in the ecosystem by acting as pollinators, seed dispersers, as well as insect population control. We are happy and fortunate to have them at Bluff Lake!

American Beaver (wetland) - Bluff Lake’s beavers live along Sand Creek and they chew down cottonwoods throughout the site (as seen in the photo above, taken December 2008). Beavers are mammals and have several adaptations that allow them to spend most of their time in water, including a gland that excretes an oily substance that waterproofs their fur, an extra, clear eyelid that allows them to see when under water, and valves that close to keep water out of the nose and ears.

More information can be found at enature.com and wikipedia.org.

Blue Grama -  Blue grama is the Colorado state grass. It grows naturally all over the United States. You will find blue grama at Bluff Lake growing in bunches along the trail. On the end of the stalk is a line of seeds that look like eyelashes. These seeds provide a great food source for animals in the winter when there is little food to be found.

photo by Courtney Keller

Cattail - You can’t miss the cattails that grow thick in the wetland area. In the summer they can grow to be over 7 feet tall. The fuzzy brown part on the top is really thousands of seeds that burst open in the winter, sending seeds flying in the wind for miles. The cattails provide a great hiding place for many animals. Look for flattened areas of cattails where the deer have made beds.

Coyote (prairie) - Coyotes look very similar to wolves, but they are much smaller. Their coat blends in with the various shades in the prairie. Coyotes are mostly active during the day when they are hunting for small prey like rabbits and small rodents. When coyotes hunt in groups they can catch much larger prey, like mule deer.

Click here to access more information from Denver’s Department of Parks & Recreation about coyotes, their role in the urban ecosystem, and hazing them in your backyard or neighborhood. Where BLNC agrees that coyotes should be hazed in housing areas, please refrain from hazing them at Bluff Lake unless they are acting in an aggressive manner.  Hazing refers to methods used as deterrents to get an animal out of an area or discourage undesirable behaviors.

Eastern Cottontail Rabbit (prairie and grassy wetlands) - Cottontails get their name from their fluffy white tail. They can live in a variety of habitats, but need to be able to dig burrows for their homes. Cottontails are herbivores that eat grasses and flowering plants. In the winter they eat twigs and small trees. In the spring and summer they can have up to 8 litters with an average of 4 young per litter. The young are ready to leave their mother within 2 to 4 weeks.


photo by Fran Haas

Great Horned Owls – Great Horned Owls are typically 18-25 inches long with a wingspan of 36-60 inches and weigh 32-60 ounces. As is typical for raptors, females are generally 10-20% larger than males. Great Horned Owls start their mating activities in December, nesting in January and February. The female usually lays two eggs, but sometimes up to four. She does all the incubation, which lasts an average of 33 days. The male hunts at night and brings food to the female. At 6-7 weeks after hatching, the owlets leave the nest (before they can fly) to sit on the tree branches and then start flying at 9-10 weeks. The parents will continue to feed them well into the summer. By autumn the young owls are off on their own, but have been known to hang around until the parents start mating behavior again in December. The young will not mate for a couple of years. Please click here for more photos of Great Horned Owls and to hear recordings of the sounds they make.

Mosquitoes (wetland) – Mosquitoes live in two different habitats: during their larval phase they live in the water (providing nutrients for many aquatic creatures) and during their adult phase they live on land (providing an important food source for birds, bats, and dragon flies). Mosquitoes can also be considered home bodies, most of the time they remain within one mile of their breeding site. Believe it or not, mosquitoes are primarily nectar feeders; many people do not realize that not all mosquitoes are interested in mammalian blood. Only female mosquitoes need mammalian blood to ensure that they receive the necessary nutrients for producing offspring.

Even though we realize the ecological importance of mosquitoes for the animals at Bluff Lake, we also want to keep our visitors happy too! We strive to achieve this balance through our mosquito management program. We have adopted a comprehensive approach to mosquito control that includes the spreading of the natural larvacide BTI (a bacterial toxin that infects and kills mosquito larvae, but does not harm other wildlife), and the installation of bat boxes. If you would like to help out at your home, think about creating bat box in addition to getting rid of any standing water around your house.

Mule Deer (prairie) - Mule deer get their name from their large ears that are especially useful for hearing predators that may be approaching. In the summer mule deer coats are reddish brown, which changes to a darker gray in the winter. The young (fawns) are reddish with white spots. Only the males have antlers. Antlers are different than horns in that they fall off in the late winter and grow back every fall. Their antlers are made of fast-growing bony material.

Plains Cottonwood - The Plains cottonwood is a native Colorado tree that only grows close to a water source. You will find these trees along the trail as you approach the lake and by Sand Creek. Their leaves are very distinct and look like an upside down heart. In the spring they release thousands of white fluffy seeds that look like cotton. This tree provides a great nesting place for many birds, not to mention that it is the favorite food of our resident beavers. Look for trees that have been chopped down by the beaver to eat or make their home. These trees will have a distinctive point, like a pencil.

Prickly Pear Cactus  - You can find this plant growing along the hill throughout the refuge. This plant’s fruits are a great food source for many animals as well as humans. People have also eaten the stem of the plant, the green fleshy part. The spines are actually the leaves. By using this shape they conserve water which allows them to live in drier climates.

Rabbitbrush - The rabbitbrush are growing strong on top of the bluff in the gardens as well as other dry areas of Bluff Lake. This plant makes a great shelter for rabbits. Not only will they make their homes underneath the shrub, they will also eat the flowers, leaves and even bark in the cold winter months. The flower blooms later in the summer and has a very strong scent that attracts many insects, including butterflies and bees.

Raccoon (wooded wetlands) - Raccoons are omnivores (eat both meat and plants) and are known to eat almost anything including pet food and trash. They are active at night, but don’t have a great sense of sight. They use their sense of touch to find their food. Many people think they wash their food in water, but the water is used to help them feel things more clearly. They live in hollow trees, caves or in burrows created by other animals. They have five fingers that leave a print that looks like little human hands.

Red-eared Slider (wetland) - These turtles get their name from the red coloring on their head, but the red spots are not their ears. They are called sliders because of their tendency to slide off rocks and logs when startled. Turtle shells are made of keratin, the material that makes up our nails. Their shell grows along with the turtle inside. Many turtles are omnivores, eating insects and small fish when they are younger so they have plenty of protein to grow. As they get older they eat mostly vegetarian.

Red Fox (wetland) - The red fox is about the size of a large cat or small dog. Red foxes can be a variety of colors, from black to gray to red. However, all of them have a white-tipped tail. Red foxes are mainly carnivores that will occasionally eat berries and fruit if prey is scarce. Foxes are crepuscular (active at dawn and dusk) or nocturnal (active at night). During the winter they become more active in the day when it is warmer.

Striped Skunk (wetland and prairie) - Skunks get a bad name because of their bad smell, but skunks only release this odor when they are threatened. They will stamp their feet and raise their tail as a warning before the spray. Many animals will stay away from skunks to avoid the bad smell, but the Great Horned Owl, who can’t smell very well, will often choose them for dinner. Skunks are omnivores (eats both plants and meat) and eat a wide variety of food, from mice and eggs to berries and fruit.

willow wreath photo by Linda Broeren

Willow - There are many types of willows that grow at Bluff Lake. The red stemmed ones that grow close to the lake are narrowleaf willows. The ones growing along the straight section of the trail by the lake are crack willows. Peachleaf willows also grow in the area. All of these trees make great shelter and food for animals. Deer will eat the branches in the winter and beavers dine on these trees all year long.

yucca photo by Sue Schafer

Yucca - Yucca is a plant that is found only in the four corner states (CO, NM, AZ, and UT). At Bluff Lake you will find it along the bluff in great numbers. Yucca have sharp and sturdy leaves that stick around all year. In the spring they have a stalk of pink and white flowers that many insects and animals love to dine on. Be sure to visit in May when the blooms are full!

This is just a small sampling of what you might find at Bluff Lake. Come on out and explore for yourself, or feel free to write or call with questions!