Birds wearing backpacks trace a path to conservation

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Like many migratory songbirds, tree swallows are experiencing population declines in parts of their breeding range – Julia Baak

By Samantha Knight, University of Guelph and Ryan Norris, University of Guelph

With the arrival of spring, we look forward to the return of hundreds of species of migratory songbirds from their wintering grounds.

Sparrows, swallows, warblers and thrushes, among other songbirds, will be returning from their wintering sites anywhere between the southern United States and distant South America.

Some of these birds will return with a small “backpack” that has recorded their entire migration from their North American breeding grounds to their wintering grounds and back.

Birds provide important ecosystem services, such as preying on insects, dispersing seeds, scavenging carcasses and pollinating plants. Unfortunately, there have been dramatic declines in many migratory songbirds over the past few decades, with some of these populations dropping by more than 80 per cent.




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If we are to find ways to slow or reverse these declines, we must first figure out what’s causing them. Climate change, habitat loss and predation by cats are among the leading causes of bird declines.

But with the vast distances these birds move over the course of the year, it can be difficult to pinpoint the main cause for a given species — and where it’s occurring.

Migratory connections

To answer this question, we need to know where individual birds spend their time throughout the year.

We have a good idea of the range — or the total area — the birds occupy during the breeding and wintering periods. But ranges are composed of many populations, and we still have a very poor understanding of how individuals within each of these populations are connected between seasons.

Individuals from different breeding populations may remain segregated during the winter. For example, some ovenbirds winter in the Caribbean whereas others spend their winters in Mexico and Central America.

Or a bird may mix with individuals that originate from other breeding populations, such as bobolinks that mix in South America during the winter.

These patterns of migratory connectivity have critical implications for predicting how migratory songbirds will respond to environmental change.

Habitat loss — deforestation, for example — in one place can have different effects. If habitat loss occurs in a wintering area where breeding populations mix, it may have wide-ranging, yet diffuse, effects on the breeding populations. But if the habitat loss occurs in a wintering area that is occupied by a single breeding population, the effect may be more focused.

For example, habitat loss in South America will likely have range-wide effects on bobolinks, while habitat loss in the Caribbean may only influence a portion of the breeding populations of ovenbirds.

Backpacks for birds

We know that the breeding and wintering populations of most species mix to some extent, but we don’t know by how much or where in the range that occurs. By understanding the migratory network, we can predict how populations across the range will respond to future changes in the environment.

How do we determine where particular individuals go? This is where the tracking “backpacks” come in handy.

These devices, known as “archival light-level geolocators,” weigh less than one gram and are small enough to be carried by songbirds.

A geolocator fitted onto the back of a tree swallow, using a harness that loops around the bird’s legs.
Dayna LeClair

Geolocators record ambient light levels every few minutes while in use. We can then use the geographic variation in sunrise and sunset times as well as day length to locate the individual bird.

We can figure out the bird’s longitude — its east-west position — by comparing solar noon, the midway point between sunrise and sunset, with the time of day (using Greenwich Mean Time). We calculate its latitude — its north-south position — from day length.

Each backpack provides a year’s worth of daily light levels, and a glimpse into one bird’s annual journey.

Tracking tree swallows

In 2011, we began deploying geolocators on tree swallows at 12 sites across their breeding range, from Alaska to Nova Scotia and North Carolina.

These iridescent blue birds with bright white bellies can be seen foraging for flying insects in marshes and fields across Canada and the United States in the spring and early summer. Like many migratory songbirds, tree swallows are experiencing population declines in parts of their breeding range. It is unclear what is driving these declines, however they coincide with declines in several species of birds that also feed on aerial insects.

By 2015, our team, comprising 27 collaborators, had retrieved more than 140 of these devices. We tracked these birds from the breeding sites to their wintering grounds in Mexico, Central America, Florida and the Caribbean.

With this information, we developed the most comprehensive songbird migration map to date. We found evidence for a high degree of mixing within three distinct migratory flyways between the breeding and wintering grounds of tree swallows.

The tree swallow migratory network.
Norris Lab

The tree swallow network

When we analyzed the network, we discovered that tree swallows migrated between their breeding and wintering grounds using three distinct migratory flyways: West of the Rocky Mountains, down the Mississippi River valley and along the Atlantic coast. Breeding populations within these flyways mixed extensively with one another at migration stopover and wintering regions.

We identified important regions within these flyways, such as areas in Florida, Louisiana, North Dakota, South Dakota and the U.S. Midwest, where tree swallows from many different breeding populations congregate. Such areas appear as critical connections within the whole network.

Now that we know more about the connections between breeding and wintering tree swallow populations, we can use this information to investigate threats to declining populations across their range. For example, using chemical markers, range-wide connectivity has been described in eastern North American monarch butterflies and then used to identify the primary threats in this declining population.

The ConversationThis spring, as the migratory songbirds return, take a moment to think about the amazing journey these birds have taken since last autumn — while wearing their backpacks.

Samantha Knight, Lab manager and researcher, University of Guelph and Ryan Norris, Associate Professor, Member of the Royal Society of Canada’s College of New Scholars, Artists and Scientists, University of Guelph

This article was originally published on The Conversation. Read the original article.

How to fight Insectageddon with a garden of native plants

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A giant swallowtail butterfly feeds from the flower of an alternate-leaved dogwood.
(Nina Zitani), Author provided

by Nina M. Zitani, Western University

People across North America love to garden, yet the vast majority of garden plants are non-native species.

Day-lilies, peonies, roses, chrysanthemums and butterfly bushes, just to name a few, are all non-natives. They evolved in far-away places such as Europe and Asia and people transported them to North America.

With Insectageddon — the great insect die-off — upon us, it’s time to rethink our gardens.

Habitat destruction is the primary cause of the decline in biodiversity. Around the world, wildlife habitat has been destroyed by a variety of human activities such as residential and commercial development, agriculture and mining operations.

But gardeners can help to reverse the trend in biodiversity loss by creating backyard habitat, and native plants are the key.

Gardening with native plants has a long history in North America, but it remains under the radar of mainstream gardening. It’s time we embraced our native plants and the biodiversity that comes with them.

Our feathered — and furry — friends will thank us for it.

And if you’re an insect hater, now might be a good time to rethink that attitude.

Many insects are picky eaters

It was hot and steamy in the Costa Rican tropical forest. I was looking for caterpillars — the cute, wiggly, multi-legged and often furry larval stages of moths and butterflies.

As a graduate student at the University of Wyoming, I wasn’t studying caterpillars per se, but looking for new insect species. My job was to search for parasitoid wasps — minute, non-stinging wasps that spend their immature stage living inside caterpillars.

I collected the caterpillars in plastic bags along with the fresh green leaves they were feeding on, and brought them back to the field station for rearing.

But before I knew it, I was headed back into the forest. The caterpillars were leaf-eating machines and needed fresh leaves often. But I couldn’t just go into the forest and grab some leaves. I had to find the exact plant species the caterpillars were eating, or they would starve and die.

And that’s how I learned that caterpillars, most of them anyway, are picky eaters.

The caterpillar of the giant swallowtail butterfly feeds on the leaves of hoptree.
(Nina Zitani), Author provided

Neatly tucked away in the scientific literature, you’ll find the fascinating story of plant-animal co-evolution that began millions of years ago during the Mesozoic Era. There are many outcomes of that co-evolution, such as pollination, seed dispersal and the close relationship caterpillars (and other plant-feeders) have with their food plants.

Today, flowering plants produce toxic chemicals in their leaves to deter animals from eating them. But some animals, namely caterpillars, have adapted to eat the plant leaves — toxins and all.

So if you’re interested in creating wildlife habitat in your backyard, then you’re going to need the favourite food plants of insects. Insects will then thrive in your garden — as will the many larger animals that depend on insects for food.

What is a native plant?

To better understand the concept of a native species, consider common milkweed and its relative, the dog-strangling vine.

Both are members of the milkweed family and found today in North America. Common milkweed is a native plant — it evolved in North America thousands of years ago, along with some other animals, including the monarch butterfly and the milkweed tussock moth. Today it is vital to the survival of those species.

But dog-strangling vine is a non-native plant from Europe that was introduced to North America by settlers in the 1800s. Monarch caterpillars and other native milkweed specialists that hatch on dog-strangling vine die because they can’t eat it.

To make matters worse, dog-strangling vine has become an invasive species, forming dense colonies that displace native plants and their associated animals, contributing to biodiversity loss.

(No, it does not strangle dogs, by the way.)

Planting for the birds

Birds (and other larger animals) depend on bugs. “Nearly all terrestrial birds rear their young on insects, not seeds or berries,” writes Doug Tallamy in his book Bringing Nature Home.

A simple way to think of it is this: Native plants maintain natural ecosystem food webs, whereas non-native plants don’t. Native plants will attract and support healthy insect populations in your garden, which will provide essential food for birds and other animals.

There are thousands of native, or wild, North American pollinator species, including approximately 4,000 native bees and about 700 native butterflies, not to mention other pollinating insects such as moths, flies and beetles.

The leaves of native plants provide the food for caterpillars. The flowers of native plants provide food — pollen and nectar — for the pollinators.

When we consider the entire life cycle of insects, the essential role of native plants becomes clear.

A caterpillar and a bumblebee on native Carolina rose.
(Nina Zitani), Author provided

And let’s not forget the non-native honey bee, one of the few domesticated insect species. Although the honey bee is not wildlife, it does pollinate some crops and produces honey. It too will find plenty of food in a native plant garden.

Small gardens, big impact

My family kicked off our native garden by planting a single common milkweed plant into our tiny urban garden. The following summer it bloomed, and when a monarch butterfly landed on it, we were hooked.

When we moved to a larger property years later, we decided to create a monumental garden full of biodiversity.

We travelled for hours to purchase plants from nurseries that specialized in locally sourced native plants. Over several years, we planted more than 100 native species, including two kinds of milkweed, nannyberry, daisies of all sorts, multiple kinds of roses, dogwoods, elderberry and more.

We also planted hoptree (Ptelea trifoliata, a Citrus relative), the food plant for the caterpillar of the giant swallowtail, North America’s largest butterfly.

A monarch butterfly gathers nectar on a native daisy commonly called cup plant.
(Nina Zitani)

You don’t need to have a huge garden to support wildlife. Start small, and plant just one native plant. Butterfly milkweed is a great choice, but there are thousands of native species to choose from. Starting small is better than not starting at all.

It’s easy to get started. The Nature Conservancy of Canada publishes the “Native Gardening 101” guide. The USDA Plants Database has species range maps for all of North America and allows you to search on common names of plants such as butterfly milkweed. The Ontario Invasive Plant Council’s “Grow Me Instead” guide includes many native plant options.

Nature Needs Half is a growing conservation movement. A reasonable end goal might be to devote half of your garden to native plants.

A year after we planted the hoptree, we spotted a giant swallowtail butterfly laying eggs on its leaves. Several days later we found the caterpillars eating the leaves, and we celebrated.

The ConversationBut not for long — we had gardening to do!

Nina M. Zitani, Assistant Professor of Biology, part-time, Western University

This article was originally published on The Conversation. Read the original article.