Songs of Stridulation

 

Immature katydids, called nymphs, are initially wingless. 

As the summer temperatures heat up, songs of singing insects fill the air with a variety of sounds.  Members of the order Orthoptera, including katydids, crickets, and grasshoppers, produce a variety of sounds through stridulation, or the rubbing of one body part against another.  

Differential Grasshopper, Melanoplus differentialis

While grasshoppers typically stridulate by rubbing their hind legs against their closed wings, katydids and crickets have modified bases of their wings in order to produce sound.  Specifically, they have a sharp edge or ‘scraper’ on the upper surface of the hindwing which they rub against a row of bumps or ‘file’ on the underside of the forewing. During sound production, katydids and crickets elevate their wings and move them rapidly back and forth, and the wings vibrate as a result of the scraper rubbing against the file.

Central Texas Leaf-Katydid, Paracyrtophyllus robustus

Unlike Orthoptera, male Cicadas in the order Hemiptera produce sounds through a pair of special ribbed organs or ‘tymbals’ located on sides of their abdomens, just behind their wings. When they contract their muscles, it causes the ribs to bend suddenly, producing a sound that resonates within a large air sac in their abdomen. The distinctive sound that is produced is one of the loudest made by any insect.

Resh Cicada, Megatibicen resh

The use of sound is crucial in courtship, with each species having its own distinct song.  Males attract mates through stridulation, producing a vibration frequency that is species-specific.  Songs are distinguished both by their dominant frequency and the details of their timing patterns. Crickets generally produce musical trills of continuous notes often too fast to count, or short bursts of chirps followed by silence.  

Field Cricket, a species in the Gryllinae family

Katydids and grasshoppers have high-pitched songs, composed of atonal shuffles, rattles, scrapes, buzzes, or ticks.  Some sing more or less continuously while other species have long silences in between periods of singing.  Cicada songs are the most penetrating, as rattling buzzes or harsh trills, often with a pulsating or grinding quality.

Fork-tailed Bush Katydid, Scudderia furcata

While most insect songs are the calling songs of males intended to attract females, these songs are thought to have other functions as well.  Some songs are for courtship once a mate is found, and some serve to attract males to a group chorus or to keep males optimally dispersed within a singing colony.  Aggressive songs can also be heard, when two males encounter each other, or even disturbance calls, when an insect is touched or handled.  Whatever the reason, now is the season to hear the songs of stridulation!

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! 

Umbraphilia!

 

Would the clouds cooperate during the total solar eclipse?

A total solar eclipse occurs when the moon, the sun, and the earth align such that the moon appears to completely cover the face of the sun from the earth’s perspective.  To see this astronomical phenomenon, you must be somewhere within what is called the path of totality.  About every 18 months or so, a total solar eclipse happens somewhere in the world, and on April 8, 2024 Central Texas was lucky enough to be in the path of totality.

Typically, the path of totality across the globe is around 9000 miles long, but only about 90 miles wide, and being in the very center of this path allows you to maximize the amount of time that totality lasts.  A total solar eclipse can last for several hours, but totality can only range from a few seconds to seven and a half minutes. Observers outside the path of totality may only see a partial solar eclipse. 

The first stage or partial eclipse.

There are five different stages that make up a total solar eclipse. The first stage is when the partial eclipse begins, or when the moon starts to become visible over the sun, looking like it has taken a bite out of it.  The second stage is when the total eclipse begins, when the moon covers the entire face of the sun, and you are now in the umbra, or the darkest part of the moon’s shadow. The third stage is totality, which is when the moon completely covers the sun and leaves only the sun’s corona visible. The midpoint of this stage is called the maximum eclipse. 

Totality or maximum eclipse!

During totality, the sky goes dark, the temperature falls, a light breeze picks up, and the birds and other animals go quiet. The fourth stage is when the total eclipse ends, and the moon starts moving away as the sun reappears.  The fifth and final stage is when the partial eclipse ends, as the moon is no longer visible over the sun.

Baily's Beads appearing in Stage 2, just before totality.

During the second and fourth stages, when the moon is just about to cover the sun or just starts to move away, those in the path of totality can have the chance to see two special effects, Baily’s beads and the diamond ring. About five seconds before and after totality, Baily’s Beads appear as little bead-like blobs of light at the edge of the moon, created by sunlight passing through the gaps in the mountains and valleys on the moon’s cratered surface. They are named after Francis Baily, an English astronomer who observed and described this effect in 1836. 

The diamond ring in Stage 4, just after totality.

About 10 to 15 seconds before and after totality, the solar corona or outer atmosphere of the sun becomes visible, and combined with a small remaining or emerging part of the sun’s disk dazzles like a diamond set in a ring.

Prominences seen during totality.

Sometimes, during totality, observers can see small, fiery structures around the obscured sun.  Typically, these are not solar flares, which are explosions on the sun’s surface that can launch massive clouds of plasma, but rather they are called prominences or longer-lived plasma structures that are smaller and not as explosive as flares.

One who is addicted to the glory and majesty of total solar eclipses is called an umbraphile, or ‘shadow lover.’  If you have personally experienced this amazing phenomenon of basking in the moon’s darkest shadow, you too may have contracted umbraphilia!

Requisite Night

 

Light pollution is nearly non-existent in Big Bend,
allowing for spectacular star-filled night skies.

Most environmentally-minded individuals recognize the more talked about threats to our native wildlife, such as habitat fragmentation/loss, invasive species, and climate change, but not as many are aware of the dangers posed by light pollution. Up until the mid-1800s, humans and animals lived under night skies solely lit by the moon. Electric outdoor lighting became common in the early 20th century, but its use spread quickly, and the global extent of modern light pollution became clear.  

By 2016, it was possible to measure nocturnal artificial light with the advent of a comprehensive global satellite measurement system. Researchers found that more than 80% of the world’s population lived under light-polluted night skies, or skies where the glow of artificial light is significant enough that the stars disappear from view.  In the US and Europe, it was found that 99% of residents live under light-polluted skies.

Light pollution exposes animals to many dangers, including predators, starvation, exhaustion, and disorientation. Artificial light, like roads and fences, can create barriers that fragment habitat.  Slow-flying bats avoid feeding in or passing through illuminated areas for fear of predators such as owls and other birds of prey. Artificial light near their roosts can also delay their emergence at dusk when their insect prey is most abundant.  If they never leave their roost since it always appears to be light, they can even starve to death.  

Artificial nocturnal light can also lure animals in and lead to their destruction.  Many species of migratory songbirds are attracted to brightly lit structures at night, circling them, sometimes colliding into them, or becoming disoriented enough to lead to a depletion their energy stores which ends in exhaustion and the inability to complete their journey.  In some bird species, artificial light at night interferes with their ability to use natural polarized light from the sky to calibrate their internal compass.

Artificial light at night attracts insects, like this Luna Moth, 
and can disrupt normal behavior patterns.

Light pollution is also one of the many factors contributing to the rapid decline of insect populations.  Moths and other nocturnal insects orient themselves by moonlight, and this instinctual tendency is interrupted by artificial night light, luring them in to fly incessantly around a bright light, causing exhaustion, exposure to predators, and the potential to miss courtship cues from mates.  This is especially true for fireflies, as artificial night light can cause them to alter or cease their mating flashes.  Studies have also shown that light pollution can harm diurnal insects like monarchs, who flit and flutter all night when exposed to excessive light when they should be resting, and causing them to be disoriented from their migration route.

Light pollution facts and some easy solutions.

Unlike other environmental threats to wildlife, simple solutions to artificial nocturnal light exist.  The best solution is to have no nocturnal lighting other than natural conditions. If a light at night is truly needed, the amount that spills into wildlife habitat can be reduced through dimming, downward shielding, or switching to motion-activated lights. Studies are also showing that lights in the warmer color tones are less disruptive than bright white lights.

Travis Audubon promotes the Lights Out Initiative for Austin.

Austin is one of several cities across the US that participates in the migratory bird friendly Lights Out Initiative, which asks residents to turn out all non-essential lights from 11pm to 6am every night during spring migration (March 1 – June 15) and fall migration (August 15 – November 30).  This is one of many ways we can prevent light pollution from overpowering our native wildlife. Turn out your lights when they are not needed, and welcome the requisite night!

Irruption Disruption

Pine Siskins often feed in groups or flocks

While many northern species of birds fly south through central Texas during fall migration, some species go no further, and spend their winters in the area. Our generally mild winters and higher availability of food sources are the reasons they stay, fueling themselves in the cooler months as they prepare for northward migration in the spring.  

This cycle is not always predictable, however, as there are a few overwintering bird species that are nearly absent in some years, and overly abundant in other years.  One such species is the Pine Siskin (Spinus pinus), a small finch-sized, seed-eating bird with a sharp pointed bill, short notched tail, and streaky brown overall with subtle yellow edging on the wings and tail.  They flash yellow wing markings as they flutter while feeding or burst into flight, and usually occur in fairly large, gregarious flocks.  Their wheezy twitters are a dead giveaway, and they will stay all winter near a dependable food source.  

Pine Siskin showing the yellow edging on wings and tail

Pine Siskins range widely and erratically across North America every winter in response to seed crops, and flocks may monopolize your feeders one winter and be completely missing the next. In the winters when Pine Siskins are abundant, the phenomenon is referred to as an irruption.  In the bird world, irruptions, broadly defined as sudden changes in population density, refer to the movement of northern-wintering bird species to the south in years of low food availability. However, some recent bird banding studies suggest that some pine siskins fly west to east while others fly north to south in search of winter food.

While fairly common, the overall population of Pine Siskins is difficult to estimate due to their unpredictable seasonal movements.  However, this species is considered to be in steep decline, with an estimated 69% decline in numbers from 1966 to 2019.  Natural threats include predation by outdoor domestic cats, squirrels, hawks, and jays.  Man-made threats include pesticides, mineral deposits from salts used to melt ice and snow, outbreaks of salmonella from unsanitary feeders, and forest clearing.

Pine Siskins will quickly empty your feeders!

Winter flocks of Pine Siskins can be aggressive around food sources, often trying to disrupt and challenge feeding competitors by lowering their heads and spreading their wings and tail. They may even lunge toward and pick fights with other seed-eating birds such as Lesser Goldfinches and House Finches. Keep an eye on your feeders this winter and you just may witness this irruption disruption, when flocks of these birds can eat you out of house and home!

Odd Ducks

Waterfowl in winter's morning mist on Lady Bird Lake.

Wintertime is the perfect time to look for ducks in central Texas.  Several species that breed far north of our state’s border return to Texas in the colder months to feed in our unfrozen freshwater lakes and rivers.  From the Old English ‘duce’, the word duck is a derivative of the verb meaning to duck or dive, or bend down low as if to get under something.  It best describes the way many ducks feed, by upending or diving under the water in search of a wide variety of food sources, such as small aquatic plants, grasses, fish, insects, amphibians, worms and mollusks.

Most ducks fall into either the dabbler or diver category.  Dabblers feed on the surface of the water, and sometimes on land, while divers disappear completely beaneath the surface and forage deep underwater.  In general, divers are heavier than dabblers, which gives them the ability to submerge more easily, but they often pay the price by having more difficulty when taking off to fly. 

While there are several species of ducks that are commonly found in central Texas winters, those that are more rarely seen usually occur singly or in small numbers.  These ‘odd ducks out’ include species such as the Hooded Merganser (Lophodytes cucullatus), Redhead (Aythya americana), and Cinnamon Teal (Anas cyanoptera).

A pair of Hooded Mergansers (female behind, male in front).

The Hooded Merganser is an uncommon diving duck that is found on forested wetlands, rivers, and backwaters. The male has a black bill and head, with a large white head patch that is conspicuous and fan-shaped when the elegant crest or hood is raised.  His black and white breast and back gives way to chestnut sides.  Females are generally browner, including their bushy crest, with some white only in the wing feathers.  Hooded Mergansers are one of the few species of ducks that nest in tree cavities rather than on dry ground near water, and the females may start scouting for next year’s tree cavity at the end of each breeding season.

A handsome male Hooded Merganser with his crest on full display.

The Redhead is a locally common diving duck, with the male having a rounded chestnut head, black breast, and smoky gray back and sides.  The female is tawny brown with a mostly slate bill with a pale band bordering a black tip.  The male’s bill is similarly patterned, but is mainly pale blue instead of slate.  Redheads prefer ponds and lakes with open waters, and sometimes winter in large flocks called rafts.  They fly faster than most ducks with a rapid, shallow wingbeat, and are sociable ducks that are usually found feeding with other duck species in a mixed flock.

Redhead ducks are aptly named.

An overall cinnamon color distinguishes the male Cinnamon Teal from the rich brown of the female, but both have a teal blue forewing patch.  The male also has a white face crescent and a vertical white flank patch.  Cinnamon Teals are dabbling ducks that can be sometimes be found on quiet marshes, ponds, and lakes in winter, typically near the edges of vegetation.  Males molt soon after breeding, but regain their rich reddish plumage by midwinter. While this species is not endangered, its population is declining due to pollution, recreational hunting, and the loss of wetland habitat.

Cinnamon Teal prefer wetland habitats with emergent vegetation.

The next time you venture out to a lake, river, or pond this winter, check the water’s edge and scan the flocks to see if you can spot one of Austin’s odd ducks!   

 

Phenomenal Phenology

 

The color-changing and dropping of leaves is a seasonal process.

Defined as the study of cyclic and seasonal natural phenomena, phenology is critically important in relation to climate and both plant and animal life.  The timing of biological events can be shifted earlier or later by climate variations in temperature, precipitation, and sunlight. Events such as migration, egg laying, flowering, and hibernation are all influenced by these climatic factors.  

Early blooming plants support early spring-emerging insects.

While ecosystems are resilient enough for normal phenological variations, major shifts may indicate a change in normal climate patterns.  These shifts can give rise to larger problems, since all life is interconnected.  In many areas of the world spring events are occurring earlier and fall events are occurring later than they have in the past. But since not all species are changing at the same rate or direction, mismatches are bound to occur.  

Nectar-producing flowers need to bloom in time for migrating hummingbirds.

Flowers that bloom too early leave fewer nectar sources for migrating hummingbirds.  Early flowering also leads to earlier fruiting, which typically yields lower quality fruit for fruit-eating migrating birds.  Many bird species time their nesting and egg-laying efforts so their eggs hatch when insects are available.  The emergence of insects depends on leaf out of their host plants.  One seemingly subtle shift in plant phenology can change entire food webs.  

Nesting and egg-laying are timed to coincide with insect emergence.

Some examples of phenology studies that are easy to perform include the date of emergence of flowers and leaves, the first appearance of migrating birds, the first flight of butterflies, the dates of egg-laying of birds and amphibians, and the date of leaf color changes and dropping in deciduous trees.  Studies can be formal or informal, and while many citizen scientists note these kinds of changes over the years, imagine if hundreds of thousands of them standardize their recording techniques and enter their data into a database that anyone can access.  This describes Nature’s Notebook, a web-based monitoring program of the USA National Phenology Network (www.usanpn.org). 

Anyone can contribute to the USA National Phenology Network's database.

Nature’s Notebook’s vision is to “provide data and information on the timing of seasonal events in plants and animals to ensure the well-being of humans, ecosystems, and natural resources.”  Its mission is to “collect, organize, and share phenological data and information to aid decision-making, scientific discovery, and a broader understanding of phenology from a diversity of perspectives.” Scientists use phenological data for critical applications such as understanding the timing of ecosystem processes like carbon cycling, assessment of vulnerable species and ecological communities, and invasive species and forest pest management.  Phenological data are immensely useful indicators of change, so considering joining the movement to document the changes you see in nature’s calendar, and watch what happens!