March 2021 – Discover-Nature

Red-winged Blackbird

Signs of spring continue in many places this month, and one of those is the return of red-winged blackbirds, Agelaius phoeniceus. Males are a glossy black with bright red shoulder patches bordered in yellow called epaulets. Females are dark, streaky brown with an orange-ish face and chin and faint pale orange epaulets. Members of the blackbird family, they have stocky, rounded wings, a short tail, and a thick beak.

Red-winged blackbirds winter in Mexico and migrate in spring to the United States and southern Canada. Wetlands, including marsh, wet meadow, and heavily vegetated shores of small ponds, are their preferred habitat. Nests are built in wet, brushy areas. They are cup-shaped, woven from twigs and grass, and attached to straight, vertical shoots near the water’s surface. They are held together with mud and lined with fine grasses for comfort and insulation.

Red-winged Blackbird song and call recorded on the Cub Lake Trail in Rocky Mountain National Park. Note that an American Robin, Ruby-crowned Kinglet, Wilson’s Snipe, House Wren and the buzz of a hummingbird flying by can also be heard in the recording.

Males arrive first in the spring and select a territory. They have a wide variety of songs for attracting mates and warning other males to stay out of their territory. Many blackbird species have the ability to learn and incorporate new songs into the repertoire. Males use many convoluted flight sequences that show their bright red and yellow epaulets as warning signs for both competitors and potential predators. Experiments studying the red shoulder patch shows that birds use them to establish a rank in the social order of birds in the area. A bird defending its own territory will display the whole epaulet, whereas a bird searching for food outside its established range will keep the red shoulder partially concealed, so as to not provoke an attack.

Females choose their mates, based in part on the amount of territory a male can hold and defend and by habitat quality. If there is enough vegetation to support multiple nest sites and insect populations for food, this is a clear indication of a highly desirable breeding partner and more than one female may choose to mate with the same male. Timing of egg laying is tied to availability of food. Females will have two broods each year, with three to four eggs in each.

Red-winged Blackbird eggs by Iowa Cooperative Fish&Wildlife Research

Red-winged blackbirds are extremely bold birds. They are not afraid to attack predators much larger than themselves. Any potential threat close to a nest site is subject to warning calls, displays showing the red epaulets, and dive bombing from a male willing to use his beak as a weapon. Threats may include crows, hawks, raccoons, and people.

Red-winged Blackbird song and call recorded in Moraine Park in Rocky Mountain National Park. Note that Western Chorus Frogs and the buzz of a hummingbird flying by can also be heard in the recording.

The red-winged blackbird is one of the most prolific species in the U.S., and yet their populations have declined an estimated 30% in the last 50 years. Some of this is due to intentional poisoning of large flocks that have often been perceived as a threat to corn and wheat granaries. Urban development continues to contribute to loss of habitat. Other causes for this decline are climate-based including late spring cold snaps that may kill off expected insect populations used for food and additional acreage under threat of wildfires due to warming temperatures.

In spring, the males sing several melodies followed by their signature drawn-out, raspy trill. If you have any wetland areas nearby, visit these to observe their courting and breeding behaviors or attract them to your backyards with their favorite foods. They generally feed on the ground or from a platform feeder. In early spring, they like sunflower seeds, cracked corn, millet, oats and peanut hearts. As insect populations arrive, birds will move into wetland areas to lay eggs and raise their young.

Sandhill Cranes

For the past week, we have been hearing warbling sounds from high overhead as sandhill cranes return to their spring breeding areas from their winter stay in Mexico and the southern U.S. Even though their large size makes it possible to see these birds for long distances, they fly at such high altitudes that their size looks deceptively tiny, making them hard to find in bright daylight skies. Flying in a ‘V’-shaped pattern, flocks from a dozen to several hundred noisy birds pass by repeatedly during the day.

Sandhill crane, *Antigone canadensis* by Brendan Lally

Sandhill cranes, Antigone canadensis, are classified into five subspecies. Lesser sandhill cranes, A.c. canadensis, and greater sandhill cranes, A.c. tabida, both overwinter in Florida and Mexico. In spring, they migrate north to breeding grounds in the northern U.S. and across Canada into the Arctic, Alaska and northeast Siberia. There are two separate flyways, one from Florida bearing slightly northwest and passing through Indiana and Illinois. The second is from Mexico heading due north through Texas, Nebraska, and Colorado. Three quarters of all the cranes will pass through the Sand Hills region of Nebraska from which their name is derived. This flock, crossing the Platte River area in spring, is comprised of 250,000 to 500,000 birds. There are three small populations of non-migratory birds named for their respective locations including the Florida sandhill, A.c. pratensis; the Cuban sandhill A.c. nesiotes, and the Mississippi sandhill, A.c. pulla.

Sandhills are large birds, standing between 3’6″ and 5′ tall. Their broad wingspans of up to six feet provide enough power to lift their considerable weight, for a bird, of six to fourteen pounds. They have a small head, long straight bill, a long neck, and a short tail covered by drooping feathers called a “bustle”. Cranes are slate gray with pale cheeks and black legs. Adults display a bright red crown and some rusty tones in their backs from mud used in preening.

Sandhill cranes in flight by Karen & Brad Emerson

Birds fly during the day when the sun is up and air currents are strongest. The birds will use thermals, a column of air that is heated by the sun and rises upwards, to carry them aloft. As cranes ascend, they are searching for air currents blowing in the direction they want to fly. Typically, they will fly between 4,000 and 5,000 feet high, but may ride a thermal all the way up 12,000 feet. Cranes are able to cover 150 to 400 miles each day at speeds of 15 to 50 miles per hour.

Sandhill cranes in flight by NPS Shan Burson

Upon reaching their summer breeding grounds, both sexes will engage in courtship displays that includes a dance involving outstretched wings and head pumping, bowing and leaping into the air. Males and females will call in unison as part of their bonding. They mate for life, only taking another partner if one dies. A normal life span is a little over twenty years; the oldest recorded bird was 36 years 7 months old. Females may begin breeding as early as age two, but most are seven years old and up. They will lay 1-2 eggs, but normally only one survives. The juvenile, called a ‘colt’, will remain with the parents for 10-12 months, until leaving for their own life the spring following their birth.

Sandhill cranes feeding in marsh by NPS & MSU Acoustic Atlas-Jennifer Jerrett

Fossils found in Nebraska date from the Miocene period about ten million years ago. The bone structure of the fossils is the same as what is found in today’s birds, making the sandhill crane one of the oldest species of birds. In the late 19th century, they were hunted for the wild meat market until they were considered extirpated east of the Mississippi River. The Migratory Bird Treaty Act of 1918, passed with support of several early conservationists, is considered to be the critical step that saved the sandhill crane. Current populations are doing well, but growing slowly since only one chick is born annually. Conservation of all five species, especially the non-migratory birds, is tied to the preservation of wetlands for migratory staging and breeding.

Now is the time of year to get outside in late morning through the afternoon and listen for their warble, then see these great flocks heading northward overhead. To learn more, take a look at the International Crane Foundation website at: https://www.savingcranes.org/

Bird Nests

Winter is quickly turning into spring in our area. Freezing temperatures that were here just two weeks ago have passed, and daytime temperatures are warm with temperatures often staying above freezing overnight. In the local bird communities, we are beginning to hear males singing for mates. This will begin the cycle of courtship, mating, nest building and raising a new family.

As birds evolved from cold-blooded to warm-blooded animals several million years ago, they started to build nests to help keep their eggs warm. Researchers think that the first nests were simple piles of twigs on the ground in depressions or among rocky or sheltered areas. The first nests built off the ground were also made from loosely arranged twigs. There are species today who still use both of these types of nests.

Savannah Sparrow nest by Kristine Sowl, USFWS

Nests have several functions. They create a place to hide and guard the eggs from predators. They provide protection for the parent who remains with the eggs while incubation takes place. They create a place where incubation is easier in variable weather conditions. Eggs can be kept warmer and out of the wind and rain. Many nests are built in places that are already sheltered, such as lower branches of trees where wind effects are less, under large limbs or next to tree trunks that provide protection from both wind and rain. In urban areas, as well as woodlands containing a heavy shrub layer, most nests are less than ten feet off the ground. The most complex nest construction is that of a cup nest, built of mud and grass, in a tree fork or hanging from a branch or plastered to the side of a building.

Robins build a cup nest of twigs and mud in the fork of a tree or on a horizontal branch close to the trunk. Sparrows, of all species, make small cups of grass built either on or near the ground. Goldfinches build a small nest lined with soft milkweed or grasses in the crotch of a tree. Hairy and downy woodpeckers, like all woodpeckers, prefer holes in trees. Hairy woodpeckers will drill an oval-shaped hole in a dead branch of a living tree, while downy woodpeckers drill a perfect circle in a branch of a dead tree. Most woodpecker holes face east or south under a branch to gather warmth from the sun and protection from the rain. Geese build a large nest on the ground near water, typically lined with down for warmth and comfort.

Hairy woodpecker nest by Kameron Perensovich

Finding nests in late spring and throughout the summer can be quite difficult. You may try to follow a bird back to its nest, but many nests are only built by one partner, and you could follow the wrong one and be disappointed. Many birds will build a nest in one place, but will forage for food in an entirely different location. If you should walk near a nest, birds will sing or make a display to distract you. Getting out at this time of the year lets you see where many of last year’s nests were located. Take a walk before leaves are out and see how many nests you can still find from last year.

Want to learn more? There are many field guides that will have information on building nests and nesting behaviors. You may want to consider a specialty volume such as “Eastern Bird Nests” by Peterson Field Guides for explicit information on nests of all kinds.

Turnover

Area ponds have been frozen for the last several weeks due to the extremely cold temperatures we have experienced. But, thawing started last weekend which initiates turnover, the mixing of pond water as surface temperatures change with the progression of the seasons. This process happens several times each year, and has profound effects on the insects, amphibians, fish and other wildlife that live in these waters year-round.

Water can exist as a gas, a liquid, or a solid depending on its temperature. Water density and its capacity for carrying oxygen also changes with temperature. Like most other liquids and gases, cold water is heavier, denser and can hold more oxygen than warm water. However, water has a unique property in that it reaches maximum density at 39˚F (4˚C). As water gets colder, it expands, becoming lighter weight and less dense. At 32˚F (0˚C), water freezes into a solid, crystalline structure called ice, which floats on top of the denser water below. This property makes it possible for wildlife to survive below the ice.

During summer, deeper bodies of water will have layers differentiated by temperature. The top layer is warmed by the sun and atmosphere and is the warmest, with layers getting progressively cooler as the pond gets deeper. Plant matter that falls in the pond will start the process of decomposition, using light and oxygen. As decomposing material sinks to the bottom where there is less light, this process can rapidly use all of the oxygen in the lower layers. Most animal life is found in the upper layers at this time of year.

Painted Turtle, *Chrysemys picta* by Steve Hinshaw

The top layer of water is constantly picking up oxygen from wind and wave action. As atmospheric temperatures start to drop in autumn, the top layer becomes colder, denser and able to carry more oxygen. As winter progresses and temperatures continue to drop, the denser, heavier water accumulates on the bottom of the pond. Aquatic species will move to this highly-oxygenated layer to spend the winter. In spring, as ice melts, the top layers of the pond pick up more oxygen from wind and wave action. As water temperatures at the surface start to climb, approaching 39˚F (4˚C), the layering effect may disappear for a short period as the entire pond mixes to a uniform temperature and density. Wildlife will start to move toward surface areas, finding well-oxygenated water everywhere in the pond. Layering will return as top layers warm more rapidly than underlying water.

American Bullfrog, *Lithobates catesbeianus* by James Harding

Northern Leopard Frog, *Lithobates pipiens* by James Harding

In Dupage County, Northern Leopard Frogs, Lithobates pipiens, American Bullfrogs, Lithobates catesbeianus, and adult Painted Turtles, Chrysemys picta, all spend the winter underwater. Painted Turtles burrow into the mud at the bottom. They slow their metabolism down to where they only need a small amount of oxygen each day. The blood vessels in their butts are very close to the skin, and they are able to absorb oxygen from the water directly into their bloodstream. They can remain in this state for 3-4 months. Northern Leopard Frogs and American Bullfrogs also slow down their metabolisms and have a similar ability to absorb oxygen through the skin into the bloodstream. They rest on the bottom, not immersing themselves in the mud because this would prevent the oxygen rich water from being in contact with their skin.

There are many factors that affect turnover and the availability of oxygen-rich water for the animals that overwinter under the ice. A mild winter may not freeze over the ponds, leaving the water well mixed and oxygenated throughout the season. Topography of the land surrounding a pond is very important. Open ponds that receive a lot of sunlight tend to turn over rapidly and often, and will have a shorter period under ice with lots of oxygen-rich water available. Ponds closed in by land or forest canopy will experience much less wind and wave action resulting in little turnover and smaller amounts of oxygen in the water. As spring starts to arrive, be on the lookout for changing conditions as wildlife starts to emerge.