Furtive Fledglings

 

Mixed woodland of oak and juniper in Central Texas is the only breeding habitat
for the Golden-cheeked Warbler.

As the temperature rises and late spring turns to early summer, many bird species are in the throes of caring for newly hatched nestlings (still in the nest) or fledglings (just out of the nest).  As you hike through our oak-juniper forests in the western part of Austin, you just may run across young families of our endangered bird, the Golden-cheeked Warbler (Setophaga chrysoparia).

Adult Golden-cheeked Warblers arrive at their breeding grounds by mid-March, returning largely to the same areas each year and nesting from April to May. They are socially monogamous, with the males arriving before the females to establish their territory. Courtship behavior, rarely observed, involves the female collecting nesting material as the male sings a soft, twittering version of his song, flicking and spreading his wings and tail and sometimes bringing nesting material to the female. 

A male Golden-cheeked Warbler sings from a juniper to establish his territory.

The female chooses the nest site, often in a branched fork of an Ashe Juniper or Live Oak tree, and the nest is built in 4 days, camouflaged by bark strips from mature juniper trees and secured by spider silk. Females lay 3-4 eggs and for the first 3 days she broods or sits on the eggs continuously, being attended to and fed by the male. The eggs hatch in approximately 12 days, and the nestlings are altricial or born helpless and requiring significant parental care.  

Female Golden-cheeked Warblers typically don't have black throats,
but the ones that do are called 'bearded females'.

However, they leave the nest only 8 or 9 days after hatching, staying in the vicinity of their attendant parents, but usually huddled together and partially hidden in the trees. They continue to be cared for by both parents, who actively search for caterpillars and other insects in the foliage to bring directly to the fledglings.  

A fledgling Golden-cheeked Warbler.

The most obvious way to spot these furtive fledglings is by listening for the family group.  As a parent nears with food in its beak, the fledglings chip rapidly and flutter their wings, begging and hoping to be the one who gets the morsel of food.  They grow quiet once the parent takes off to forage again.  Once they get a bit older, they start to follow their foraging parents begging for food, eventually becoming more confident in their ability to fly and learning to forage for themselves. As they become even more independent, the young join the adults in mixed-species flocks in the woodlands before migration begins in July and early August.

This Golden-cheeked Warbler fledgling caught its own food!

If you hear or see a Golden-cheeked Warbler family foraging and feeding in our mixed woodlands, consider yourself lucky.  Of the nearly 360 bird species that breed in Texas, the Golden-cheeked Warbler is the only one that nests exclusively in Texas, so each one is a native Texan! 

Cooling Conduct

Eastern Ringtail dragonflies obelisking

The unrelenting heat this summer has affected all living creatures, and while humans can escape into air-conditioned spaces, wildlife needs to rely on other ways to regulate their body temperature.  Often this is accomplished through different types of behavioral strategies acquired through adaptation, and some may seem quite odd until you understand the dynamics at work.

One of the most obvious behaviors (for humans at least), is sweating.  But many creatures don’t have sweat glands, or only sweat from their feet (like some canines), so they rely on panting instead.  In panting, animals breathe rapidly and shallowly with their mouths open, thereby increasing evaporation from the surfaces of their mouths.  This evaporation removes heat and acts as a cooling mechanism.  Panting is used by most mammals (like dogs) and many species of birds. While panting is effective at removing heat, dehydration is a risk so a nearby water source is important.  Birds may also spread their wings and body feathers to allow heat to dispel, and they have an elaborate breathing system that includes air sacs (in addition to lungs) to help them get rid of excess heat through panting.

A molting Northern Cardinal, panting and spreading its wings to cool down

Some birds, such as some species of vultures and storks, will voluntarily defecate on their legs to cool down.  Since bird poop is mostly liquid, it works by having an evaporative cooling effect, much like sweating.  As the poop dries on the bird’s legs, the heat is carried away and it brings down their body temperature.  Pelicans, herons, doves, owls, quail, and nighthawks, can employ gular fluttering, vibrating the muscles and bones in the throat and exposing moist throat membranes to the air, which helps regulate temperature by increasing evaporation.

Insects, like most all creatures, can also maintain a stable body temperature in at least a portion of their bodies through some interesting behavioral means.  While many insects need some heat to warm up their flying muscles, many will adjust/reduce their activity levels or seek out shady spots to handle extreme heat.  Dragonflies, for example, will often obelisk while perched in the midday hot sun, or point the tip of their abdomen directly up at the sun.  It is believed that this behavior reduces the heating effect by reducing the amount of surface area exposed directly to the sun’s rays.

Checkered Setwing exhibiting obelisking as a cooling behavior

When temperatures soar, four-legged animals such as squirrels, marmots, rabbits, bears, and even dogs and cats will lie flat on their stomachs on a cooler surface with their arms and legs stretched out from their bodies.  This behavior is called splooting, and it is thought that since their bellies have less fur and lots of blood vessels, they can dissipate the heat and absorb some of the coolness from the surface.  Also known as frogging or pancaking, splooting can take on various forms: the full sploot (all four legs out), the classic sploot (one leg tucked underneath the body while the other is kicked back), the side sploot (one leg tucked under the body and the other kicked out to the side), and the reverse sploot or toolps (when the animal lays on its back with its legs in the air)!

Fox Squirrel in a full sploot on our back porch

Regardless of the method, we all have to find some form of cooling conduct that allows us to survive until temperatures fall and (hopefully) the rains begin once again.

 

The Real Rocky the Squirrel

 

Telltale signs of a Rock Squirrel Den

The squirrel family includes several different species that are grouped into tree squirrels, ground squirrels, and flying squirrels.  In central Texas, most are familiar with the Eastern Fox Squirrel (Sciurus niger) and the Eastern Gray Squirrel (Sciurus carolinensis), both of which are tree squirrels, meaning their habit is to live mostly among trees. The Southern Flying Squirrel (Glaucomys volans) occurs rarely in the eastern most portion of our area, and is named for the special flaps of skin on the sides of its body which allows for gliding flight.  But it is the Rock Squirrel (Spermophilus variegatus), which generally lives on or in the ground rather than in trees, that is our most notable ground squirrel.

Rock squirrels are stout, moderately bushy-tailed mammals, with mottled grayish-brown upperparts, a more brownish hind back and rump, buffy underparts, and a tail mixed with buff and brown and whitish tips.  The head and upper back are often distinctively blackish, and they have a light-colored ring around each eye. Adults are typically about 18 to 20 inches long, including the tail, and are found from central Texas westward into the Trans-Pecos region of west Texas.

Adult Rock Squirrel

As their common name implies, rock squirrels nearly always inhabit rocky areas such as cliffs, canyon walls, cervices, and rock piles, and even man-made areas like fills along highways and retaining walls.  These areas are where they seek refuge and create their dens.  Although they are typical ground squirrels, they can climb trees nearly as well as tree squirrels, where they can forage for berries and seeds, and they can scale rock walls with ease.  Their diet consists of a variety of plant materials, along with many types of insects.  Unlike many other squirrels, they are fond of flesh and can catch and eat small birds. They can survive long periods without water, some even up to 100 days.

Rock squirrels are facultative hibernators meaning they enter hibernation only when either cold-stressed, food-deprived, or both.   In central Texas they generally hibernate from November to February or March, often coming out to sun during warmer winter days.  Their populations tend to be colonial, each consisting of multiple breeding females and a dominant male.   Home ranges can be fairly large and include several different dens, and the males are thought to be polygamous.  Breeding occurs in March and April with an average litter of 4 young that emerge from the den in late spring.

A litter of 5 young Rock Squirrels

Most active in early morning and late afternoon, rock squirrels are rather shy and difficult to observe at close range. Like other ground squirrels, they are known for their tendency to rise up on their hind legs whenever they need to see over tall vegetation or when they sense nearby danger.  They then curl their front paws flat against their chests and send out a sharp, clear whistle to warn other family members if they sense the presence of predators.  Now you know more about Texas’ very own real-life version of Rocky the Squirrel!

Silent Flight

Eastern Screech-Owl

Owls have fascinated man from time immemorial – to some cultures they are symbols of wisdom, while to others they are harbingers of doom and death.  Adding to the mystique of these creatures is that they are mainly active at night, using their exceptional vision, acute hearing, and silent flight to stealthily hunt down their prey.

Common in Central Texas, the Eastern Screech-Owl is found in wooded suburban and rural areas and readily nests in tree cavities as well as man-made nest boxes.  A small owl 6-10” long with a wingspan of 19-24”, it has feathered ear tufts and is normally gray, brownish-gray, or less commonly reddish-brown.  The Eastern Screech-Owl eats a variety of small animals, and each night consumes from one-quarter to one-third of its own body weight.  It uses a soft trilling call to keep in contact with a mate or family members, and the male’s trill can advertise a nest site when courting a female or signal an arrival at the nest with food.  This owl also has a descending whinny, which is used to defend its territory.  Eastern Screech-Owl pairs are usually monogamous and remain together for life, although they will take a new mate when one dies.  In mid-April, the female lays 3-4 eggs on average, and the downy white owlets emerge from the nest by mid-May.

Great Horned Owl

Also common but much larger at 18-25” long with a wingspan of 40-57”, the Great Horned Owl prefers habitats of secondary-growth woodlands mixed with open meadows.  Often found perching next to an open area and nests in tree hollows, broken off snags, or nests made by other large birds.  It has prominent ear tufts spaced widely on its head, a brownish-gray body with dark barring, and a rusty facial disk edged in black surrounding each of its orange-yellow eyes. The Great Horned Owl has a broad diet of small mammals, birds, amphibians, and reptiles, and is the only animal the regularly eats skunks.  They have a large repertoire of sounds, but the most common is that of the male’s resonant territorial call ‘hoo-hoo hoooooo hoo-hoo’ that can be heard over several miles through the canyons on a still night. These owls are solitary in nature, only staying with their mate during the nesting season of January and February. Typically 2-4 eggs are laid and incubated solely by the female, until the young start roaming from the nest six to seven weeks later.  

The structure of an owl’s feather is the main reason they can fly so silently.  The leading edge of their primary wing feathers are serrated like a comb, which breaks down the turbulence into smaller, micro-turbulences.  The soft, tattered edges of their secondary feathers allow those small currents of air to pass through them and further reduce the turbulence behind their wings.  In addition, the velvety down feathers found in the wing linings and on their legs further dampen and absorb sound frequencies.  Together, these features allow the owl to greatly reduce the overall noise caused by the turbulence of air flowing over them as they fly.