By Alex Harper
Turkey Vultures, swallows, Ash-throated Flycatchers, Lucy’s Warblers, Hooded Orioles and Yellow- headed Blackbirds sneak into southern Nevada by late March and continue into early April. These species are among the most obvious returners to the region as springtime ushers in breeding and migratory activities for hundreds of birds. The pulses of birds moving into southern Nevada are driven by the instinct to breed. As the northern hemisphere warms up and trees begin to produce buds and flowers, birds come in to feed on resources that were not available during the winter and find cover in trees that were previously bare.
The movement of migratory birds in the spring is largely dependent on weather. Most songbirds migrate during the nighttime and fly on clear nights with favorable winds. Birds are in a rush to reach their breeding grounds to claim the best territory for nest-rearing. Driven by hormones that are largely signaled by increasing daylight, they want to push northward. To do this, they will need to store their energy in the their wintering grounds and bide their energy as they move northward. For this reason, birds often fly with favorable tailwinds as opposed to against energy-depleting headwinds.
Songbirds employ a few strategies to help them migrate at night. It is believed that songbirds rely heavily on stars and other features of the night sky to help them navigate, recalling the early human navigators. Perhaps just as remarkably, songbirds have demonstrated an ability to orient using magnetic fields. In the eyes of many birds is magnetite. Magnetite moves across the eyes depending on their orientation to the north and south poles, suggesting that they have the ability to always have the ability to see the magnetic fields that exist above both poles. You can think of this as having compasses in the eyes, and songbirds that migrate have higher concentrations of magnetite in their eyes than nonmigratory birds. Along with these adaptations, birds utilize and memorize landscape features such as mountain ranges, valleys and river systems. They apparently employ all of these modes for navigation in conjunction to move about the world.
Using these remarkable adaptations and navigational skills are millions of colorful songbirds that are rearing to migrate into and across Nevada in the months of April and May. To best see these species, one may not need to wander far outside of the city; many local parks and even backyards can attract a diversity of migratory species. Some of the most popular locations for viewing vireos, flycatchers, thrushes, warblers, sparrows, orioles, buntings and grosbeaks are Corn Creek Field Station, Floyd Lamb Park, Craig Ranch Park, Sunset Park, Clark County Wetlands and the Henderson Bird Viewing Preserve. These parks are easily visible to birds flying towards or over the city, have available water, and offer a variety of options for resting and refueling.
There are a few things to remember when looking for migratory birds this spring. Firstly, well-fed birds often begin migrating shortly after sundown and can fly for over fourteen hours after launching. That means that even though birding activity is overall higher around dawn that newly arriving birds may not touch down into a place that you are birding until late morning. Secondly, pay attention to the weather in the immediate area and in locations to the south where most birds are coming from. Birds move when there is a gentle tail wind coming from the south and clear skies. Do not expect to find arriving migratory birds during a period of northerly winds. You can learn how to better predict these movements by following a migration tool called BirdCast (Live bird migration maps - BirdCast). BirdCast uses weather tracking data to estimate bird traffic at night. By following weather patterns and ground truthing on your own, you can better predict the presence or absence of migratory birds. Predicting migration is difficult, so expect a steep learning-curve and deep satisfaction in the learning process.
It"s not just songbirds that move into the region during April. Waterfowl mostly move out as the month moves along, but shorebirds start to move in. Avocets, stilts, plovers and sandpipers may begin congregating at the Las Vegas Wash from Sunrise Manor down to Pabco Weird, the Henderson Bird Viewing Preserve and in reservoirs. Scan shorelines and mudflats beside water and you may well run into shorebirds. The end of April and early May is a peak period for shorebird migration. For that reason, the Intermountain West shorebird survey runs through the last week of April. Red Rock Audubon volunteers will be helping to conduct shorebird standardized shorebird surveys at key shorebird habitats across Nevada as part of a long-term population and land-use study.
In our own neighborhoods and communities, residential birds continue along in breeding activities. You will hear familiar backyard birds maintaining territories though chasing off competition, singing, displaying, and courting. By the end of the month you may hear the sounds of nestlings or see birds fledging the nest. Meanwhile in the higher elevations surrounding Las Vegas, breeding activity is more staggered. Typically mountainous birds begin breeding a few weeks later than birds in the low valleys.
As you get out and wander in April, notice that seed-eating sparrows move through before most insectivores like flycatchers and warblers. Pay attention to how diet and the scarcity of resources are connected to temperature or the life histories of species of birds. For migratory birds there is a sweet spot that must be met: they want to be early enough to claim the best territory but not so early to be wiped out by lingering cold weather. Each species has it’s own tolerance and strategies to cope. What will you observe this April?