Faces of Wetlands: Tree Swallow

Image: All About Birds

Tree swallows are a striking songbird that breeds in marshes, shorelines, wooded swamps, and fields. To quickly spot them in the field, watch for the birds sporting a flashy tuxedo. Both males and females are iridescent blue with a bright white underbelly and black facemask. Tree swallows have similarities to blue birds and other swallows, but with a closer look, we can see how unique they are and what they mean for the watershed.

With a wingspan of up to 35 cm, tree swallows are truly a bird of flight. Their wings reach back to the tip of their tail, providing strength, endurance, and agility in flight. These swift, agile wings keep them comfortable in the air as they search and devour insects without landing for a break. Streamlined bodies allow them to drink and bathe by gently skimming the water’s surface, creating a “skipping” pattern that resembles a rock skipping across water. This skill is also used for pick up pieces of aquatic plants, used for nesting material.

Unlike blue birds, chickadees, and house wrens, tree swallows line their nests with feathers. This is thought to provide warmth for chicks on cool spring nights. Early in the breeding season, tree swallows can be seen holding feathers in their beaks, dropping them mid-flight, and racing to catch them before they hit the ground. Be it play, courtship, training, or bragging about their nest, this remains one of the least understood behaviors of tree swallows. Multiple swallows have been observed competing, swooping and diving for the same feather.

As cavity nesters tree swallows, blue birds, purple martins, and other birds such as woodpeckers rely on dead or decaying trees to nest. Tree swallows saw a population decline of 49% between 1966 and 2014, largely due to the practice of clearing dead and decaying debris. However gleaning some support from the popularity of bluebird nest boxes, tree swallows have seen an increase in numbers. Because tree swallows are one of the earliest birds to arrive in spring, they often beat blue birds to the first picks… much to the dismay of blue bird enthusiasts.

Unlike other swallows, tree swallows can supplement their diet with berries. With this accessory option, tree swallows are able to survive spring cold snaps while other insect-eating birds struggle to find food. In the breeding season, a single tree swallow will consume about 2,000 insects per day. On top of their own consumption, parents can feed up to 6,000 more insects to their brood every day.

An old farmer adage goes, “when swallows fly high, the weather will be dry.” This lyrical ring has some truth to it. On hot, dry days, warm air rises. This sweeps up insects into wandering heat bubbles. To keep up, swallows follow, flying higher for a sky buffet. During migration thousands of tree swallows can flock together, pausing over various lakes and wetlands for food. Perhaps their most astounding spectacle however, occurs in their wintering grounds. In these southern states, millions of wintering swallows form flying bird tornadoes. Gathering high in the sky, they form a black cloud contrasted by an evening glow before descending to roost for the night. Click here for a video of the phenomenon in action!

Such a magnificent display may seem far away, but it connects our 500 local wetlands to a national network of habitat. As a local government agency, VLAWMO administers the Wetland Conservation Act (WCA). This policy with national and state branches works to ensure a no-net-loss of wetland resources. It can be confusing or frustrating to work around at times, but it has many benefits as well. Prior to the Wetland Conservation Act, Minnesota had already lost almost half of it’s wetland resources due to gradual but consistent conversion of wetlands into agriculture and development. Protecting seasonal and permanent wetlands supports flood control, water quality, groundwater supply, habitat, and even air quality. With responsible land and water management, events such as the swallow tornado can continue to astound us.   

Watch for swallow migrations over East Vadnais Lake in September, or learn more about the Wetland Conservation Act on our website here.

Sources: Star Tribune Sailis Audubon Society All About Birds Country Roads Magazine

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