Bird Food Grows on Trees!

Spring is here, and love is in the air for our backyard birds! After a long winter of subsisting on seeds and berries, birds need a new menu in spring. Soon they will be mating, nesting, laying and hatching eggs, and hunting from sunrise to sunset to feed their newborn chicks. That takes a lot of energy, and it requires a special diet.

Baby birds can’t eat seeds or berries. They need the protein and other nutrition found only in insects. And, though baby birds will eat a variety of insects, their favorite food is caterpillars, the larvae of moths and butterflies. Caterpillars are soft, easily digested, and loaded with nutrients. Bird parents need thousands of caterpillars to raise even a single clutch of babies. Where are all those caterpillars to be found?

 A pair of chickadees needs 7,000 to 9,000 caterpillars to raise 3 baby chicks
Photo: Doug Tallamy

Caterpillars, quite literally, grow on trees – but only on native trees! For example, not one species of caterpillar has been observed growing to maturity (to become a moth or butterfly) on Norway Maple, a non-native tree. A bird searching for caterpillars on a Norway Maple will find nothing to feed her babies. In contrast, many native trees are hosts for hundreds of different species of caterpillars, so they produce lots of bird food.

Among native trees, some species are much more productive hosts than others. Recent studies have ranked native tree species for their ability to host caterpillars. So, which are the best trees to have around if you want to feed the birds?


The undisputed MVP of caterpillar-producing trees is the native Oak (Quercus spp.). You cannot go wrong planting a White Oak (Quercus alba), Red Oak (Quercus rubra), Scarlet Oak (Quercus coccinea), Pin Oak (Quercus palustris), Bur Oak (Quercus macrocarpa), or any other Oak tree native to our region. Oaks are host plants for over 550 species of caterpillars! Think of Oaks as the grocery store for bird families.

Though this White Oak likely holds thousands of caterpillars, it is not at all disfigured by their munching!


Second only to Oaks as caterpillar factories are the small trees in the Willow family. Pussy Willow (Salix discolor) is a great garden plant and hosts over 450 species of caterpillars. (The familiar weeping willow tree, however, is not native to North America and is not a host plant.) Our recent blog post found here is full of information about Pussy Willow.

Pussy Willow is a small multi-trunked tree great for smaller gardens
Pussy Willow in bloom supports native bees

Black Cherry

Our native Black Cherry tree (Prunus serotina) and the closely related shrub, American Plum (Prunus americana), are essentially tied with Willows as caterpillar producers, with over 450 known species using their leaves as hosts. Both also produce fruit that adult birds enjoy in the summer. Black Cherry is not often planted, but if you have one in your yard, take good care of it, and the birds will thank you. American Plum has beautiful flowers, can form a dense thicket, and is a great shrub for a privacy screen if you have some space.

Wild Black Cherry is incredibly valuable to birds
Bees, butterflies, and birds all flock to American Plum


Native birches are next in line as caterpillar producers, hosting just over 400 species of moths and butterflies. River Birch (Betula nigra) is a favorite as a landscape plant, and its crazy bark holds a variety of insects that attract woodpeckers all winter. Chickadees, warblers, wrens, and many other songbirds hunt and find caterpillars in the leaves of birch trees.

River birches make lovely landscape plants
Photo: Mia Edwards
The bark of River Birch adds winter interest


Malus, the apple tree family, hosts over 300 species of caterpillars and includes the lovely crabapples that bloom so profusely in late spring. Crabapple is another caterpillar host that is of equal value to native bees because of the pollen and nectar provided by its flowers.

Crabapple in bloom


Our native Red Maples (Acer rubrum) and Sugar Maples (Acer saccharum) host 285 species of caterpillars and are gorgeous shade trees. But be sure to choose one of these natives rather than a Japanese Maple or the invasive Norway Maple, which do not host native insect species at all.

Native red maples are stunning in the Fall

White Pine

It may surprise you to know that even our native White Pine (Pinus strobus) is an impressive larval host to moths and butterflies. Over 200 species of caterpillars develop on the needles of native pines, and many of them over-winter on the tree. If you watch carefully, you may spot birds combing the branches of pines and making trips back to their nests with juicy caterpillars for their babies.

Pine trees are also caterpillar hosts

It is often said that trees are essential to life. They pull carbon dioxide from the air and store it for years. They produce oxygen, manage storm water, improve soil, provide shade, and shelter so many animals. It is easy to forget, however, that their leaves also feed the little wiggly creatures that make life possible for all of our beloved birds. Our choices – which trees to plant, which to take down, and which to care for – have a huge impact on the world around us. Choose wisely!

Share this post:

Before the Bulbs

Is it spring yet?

For many gardeners, the earliest signs of spring are snowdrops, crocuses, and daffodils. But if you know where to look, you can find blooming flowers — and the little critters who need them – even before those bulbs come to life. One of the earliest bloomers in the Northern half of the US also happens to be one of our most interesting and valuable native shrubs: Salix discolor, or the amazing Pussy Willow!

In February, Pussy Willows are already producing the adorable, fuzzy flowers that give them their common name. This type of flower has no petals or fragrance, and is known as a “catkin” from the Dutch word “katteken,” which means kitten. Just as soft to the touch as they look, the silvery catkins are popular in spring flower arrangements and delight children of all ages.

 Pussy Willows start blooming in February
The soft hairs on catkins protect the inner flower parts from cold and snow

Over the next month, the catkins will gradually open revealing numerous string-like filaments. Pussy willow shrubs are dioecious, meaning the shrub holds either male or female flowers. On the male plants, the filaments hold quantities of pollen that give the catkins a bright yellow appearance. The female flowers look more like spiny caterpillars than kittens, so for ornamental purposes, the male shrubs are preferred.

By mid-April, the catkins have opened and leaves begin to emerge

Pussy Willows typically are large, multi-stemmed shrubs or small trees, topping out between 15 and 25 feet. Unlike most trees, however, they can benefit from being severely pruned, or “coppiced,” to keep them shorter. Cutting back the branches after blooming will generate multiple slender new stems, increasing the fullness of the shrub and the number of catkins within easy reach in the following season. 

Humans have used the flexible young branches of willows for basket-weaving, arrows, rustic fencing, and many other purposes for hundreds of years. One of the most important traditional uses of willow bark was medicinal. Willow bark tea contains salicin, a pain-killer and fever reducer, now synthetically produced as aspirin.

Pussy Willow’s natural form is a large, multi-trunked shrub, but it can easily be pruned as a hedge or privacy screen

By far the most important use of Pussy Willow in our gardens, however, is to support native pollinators and other insects. As one of the very earliest plants to bloom, Pussy Willow provides nectar and pollen for early-emerging native bees. In fact, the Andrina family of native bees are willow “specialists” – they must have willow pollen to feed their young. The nectar of willow catkins also supports many other insects in early spring when food is especially scarce.

 A tiny ant finds what it needs on Pussy Willow

All summer long, the leaves of Pussy Willow feed the caterpillars of more than 450 species of moths and butterflies — second only to oak trees in providing caterpillars for baby birds! Willow is a host plant for a huge number of our most spectacular butterflies: Viceroy, Red-spotted Purple, Mourning Cloak, and various hairstreaks, fritillaries, and dusky-wings.

Mourning Cloaks are just one of hundreds of butterfly species that depend on willows

In addition to Pussy Willows, there are at least 90 species of willows native to the US, and 20 or more native to the Northeast. Unfortunately, there are also many non-native species sold in the nursery trade, including the well-known weeping willow (Salix babylonica), that do not provide the same value to our native birds and insects. Be sure to check the scientific name before you add a willow to your landscape.  Pussy Willow (Salix discolor), Black Willow (Salix nigra), Shining Willow (Salix lucida), and Silky Willow (Salix sericea) are all good native shrubs, but Pussy Willow is likely the easiest to find.

Pussy Willow is a great choice for sunny wet areas, including rain gardens. It is an ideal solution for a soggy lawn area where rainwater tends to collect. All willows have extensive root systems that seek out water, so they should not be planted near a septic system, but they are perfect near a stream or pond or anywhere you want to stabilize a slope eroded by stormwater.

Deer will browse Pussy Willow, but because the shrub actually benefits from winter pruning, the nibbling is unlikely to harm the plant. Pussy Willows grow fast and are very resilient. In fact, many people propagate them simply by cutting off a dormant stem in winter and sticking it in the ground, or even a glass of water, until roots appear. Hardy in Zones 2 through 7, the only thing Pussy Willow does not tolerate well is shade. You’ll need at least a half day of sun, and plenty of water until the roots are established. 

Pussy Willow is an all-around winner: easy to grow, interesting and attractive, incredibly valuable for the ecology, and a real problem-solver for a troublesome spot in the landscape.

So, where will you put it?


Back to School

Many of us grown-ups, upon learning of the complex relationships between native plants and insects, wonder “why am I hearing about this for the first time?” or “did I miss this in school?”  No worries! You are not alone. This subject only recently has become part of the basic biology curriculum.

At the Greenburgh Nature Center, we want people of all ages to understand this vital relationship. So, let’s start at the beginning — with some visual aids!

“Native” plants are the species that evolved in a particular place without human intervention. In the US, that means the trees, shrubs, grasses, and perennials that were here before European settlers arrived. Native plants are important largely because of their relationship with native insects. 

The majority of insects eat plants. Most other animals, including humans, also eat plants, or they eat other animals that eat plants. As the main food supply for most living things, plants would soon be wiped off the face of the Earth if they did not develop strategies to protect themselves from all of these plant-eaters!

Most insects eat plants
Illustration: Masha Role

Over the millennia, plants evolved defenses to protect themselves from plant eaters. You may recognize a few of these if you’ve eaten a very hot chili pepper or had a bad reaction to touching poison ivy. Insects (the largest category of plant eaters) face similar problems.

Plants have developed many defenses to hungry insects
Illustration: Masha Role
Toxic leaf chemicals, sticky sap, spines and thorns, stinging hairs, fibrous tissue, bloom time, and even height are evolutionary plant defenses to insect predators
Illustration: Masha Role

To survive, insects had to evolve methods of overcoming plant defenses. But the enormous variety and complexity of defenses in the plant world limited insects to overcoming only the specific defenses of a limited number of plant families. As a result, about 90% of all plant-eating insects are “specialists,” meaning they are able to eat only a few closely-related species of plants. Those plants became the “host” plants for the insect species adapted to overcoming their specific defenses.

Specialist insects eat their host plants, but cannot eat other plants. The host plants can survive and reproduce because they are eaten only by the insects specialized to them.
Illustration: Masha Role

The best-known example of this insect/host relationship is the monarch butterfly and milkweed. Milkweed has sticky sap loaded with toxins that repel most insects. The monarch caterpillar evolved the ability to tolerate those toxins, but has no ability to overcome the defenses of other plants. Monarch caterpillars cannot eat the leaves of plants outside of the milkweed family.

Monarch caterpillar on milkweed
Monarch butterflies can drink the nectar of many flowers, but must lay their eggs on milkweed

The situation is the same for most plant-eating insects. These evolutionary plant/insect relationships developed over very long stretches of time, thousands of years. So, most insects can eat only those plants that evolved with them in the same place and over the same long period of time. That is why insects native to North America cannot eat plants that have been brought in, or “introduced,” by human settlers from other continents.

As you look around your neighborhood, you will no doubt see many plants introduced from other continents: Norway maples, Korean dogwoods, Japanese maples, Norway spruces, Japanese barberry, English ivy, Chinese feather grass, and many more. These non-native plants have evolutionary relationships with insects on other continents, but most North American insects cannot eat them. Many of these plants are marketed as “pest-free” for exactly that reason. Insects here avoid them, and many gardeners like that! 

But “pest-free” plants come at a terrible cost: nearly all (96%) of our native terrestrial birds need insects to feed their young. Well-documented and shocking declines in insect and bird populations over the past 50 years tell us we are facing a crisis. Without native plants, we lose insect populations. Without insect populations, we lose birds. We also lose all of the other animals that feed on insects, as well as butterflies, fireflies, and specialist bees that pollinate food crops and most of our flowering plants. More broadly, without native plants, biodiversity itself is threatened and our ecosystems become unstable.

Fortunately, this is one crisis we can solve in our own yards. By choosing native plants, and planting a lot more of them, we can actually bring insect species back from the brink of extinction!

The Atala butterfly

A wonderful example of this is the story of the beautiful Atala butterfly, native to parts of Florida. The Atala was believed to be extinct from 1939 until the 1960’s when a small population was discovered on an undeveloped island off the Florida coast. Then, in the 1980’s, horticulturists discovered and began growing a lovely small plant called the Coontie palm (Zamia floridana or integrifolia). Coontie was once common in Florida, but it was overharvested in the wild by early settlers for its starchy root. By the 1930’s, the plant had largely disappeared from the Florida landscape. Beginning in the late 1980’s, the re-discovered Coontie became popular with homeowners and was planted in gardens and along walkways in many Florida suburbs. And suddenly, the Atala butterfly re-appeared!

Coontie is the only plant Atala caterpillars can eat

It turns out that Coontie is the host plant for the Atala butterfly! As Coontie became popular in suburban yards, the Atala butterfly rebounded. Today, this beautiful butterfly is common enough that some misguided homeowners look for pesticides to control the Atala caterpillars eating their Coontie plants!

So, hopefully, we adults are now on common ground with today’s kids. We understand that native plants are a key element in the health of our planet. If we continue to use “pest-free” non-native plants, we will continue to see our favorite back-yard birds disappear, along with monarchs, other butterflies, and the rest of the natural food web. Or, we can do a simple good thing for nature: fill our yards with native plants and provide the food so critical for life.


If You Can Do Just One Thing…

Conservationists, ecologists, and this blog repeatedly urge gardeners to use more native plants. Native plants are essential to a healthy ecosystem because they are the first link in the food chain. Insects native to a particular region generally cannot eat plants from other regions, and insects are the primary food source for birds and many other animals. We know that insect and bird populations are declining rapidly, so we ask homeowners, residents, and property managers to replace lawn, which has no ecological value, with abundant plantings of native trees, shrubs, grasses, and perennials. 

But not everyone can do that. Gardening is not everyone’s hobby and, for many people, taking care of a lawn and a few shrubs is really all they can manage. So, what if you want to help save songbirds, butterflies, and fireflies, but transforming an entire landscape to native plants is not an option? 

In a recent interview, Dr. Douglas Tallamy, research scientist and best-selling author of several books about the interaction between native plants and insects, was asked whether there are any simple things that anyone with a yard can do to benefit insects and birds. He immediately responded, “Plant an oak tree.”

Autumn foliage on a Pin Oak (Quercus palustris)
A young White Oak (Quercus alba) in summer

Planting a native oak tree — or saving one — may be the single most valuable thing you can do to support nature. Oak trees are “keystone” plants, which means they are essential to the survival of many other species. Without them, there would be a cascade of species extinctions.

 Baby birds need insects

The importance of oaks to our native birds is perhaps the most dramatic example. Virtually all songbirds need insects to feed their young. Baby birds cannot eat seeds or berries. They must have insects, especially caterpillars. Caterpillars, the larvae of moths and butterflies, are soft, easily digested, and loaded with the nutrition baby birds need. Dr. Tallamy’s research has shown that a pair of Black-capped Chickadees needs 7,000 to 9,000 caterpillars to raise a single clutch of 3 baby chicks to maturity. Chickadees are very small birds and, if there is enough food, they can raise 2 clutches of babies in a season — that’s a lot of caterpillars! All of our other backyard birds have the same needs. Adult birds spend all day finding and transporting thousands of caterpillars to their nests. And where is the best place to find all those caterpillars? On the leaves of native oak trees!

 Black-capped Chickadee with caterpillar
Photo: Dr. Douglas Tallamy

Oak trees are caterpillar factories. Over 500 species of moths and butterflies lay their eggs and hatch their caterpillars on native oak trees. By comparison, not one single species of North American moth or butterfly caterpillar can mature on the leaves of a Norway maple! In fact, none of the popular non-native trees typically planted in suburban yards help birds feed their babies. Japanese maples, crape myrtles, Korean dogwoods, Norway spruces, Callery pears, and Kwansan cherries are essentially “barren” – they do not support caterpillar populations or other insects of value to birds. 

Caterpillars of Hairstreak butterflies must hatch on oak leaves

Planting a native oak tree, or saving one from destruction, is an easy way to support biodiversity. There are over 90 species of oaks native to the US, and many of them are widely available, hardy, easy to care for, and very long-lived. In the Northeast, white oak, red oak, scarlet oak, burr oak, pin oak, and black oak are all good choices.

And you don’t need a big property to have a happy oak tree. Although an oak can reach 100 feet tall with a crown spread of 120 feet given a couple hundred years, planted in an average-sized lawn, 20 or 30 feet from house and pavement, an oak can live its long life without causing any problems. The roots of oak trees tend to run deeper than most trees, so they are less likely to buckle your driveway or sidewalk than many other species. And oaks make great specimen trees in lawn areas because they typically have a more open canopy than maples or other big shade trees. They allow enough sunlight through to permit lawn (or native groundcovers) to grow underneath.

 Oak trees do very well on average-sized suburban properties
Even mature oaks allow enough sunlight through for lawn and other plants

Oaks do best in full sun, and average, well-drained soil. Young trees will need regular watering until their roots are well-established, but once established, oaks need very little care. Professional pruning in the first decade will assure healthy branching, but supplemental water and fertilizer is rarely needed. 

It is easy to add an oak tree to any landscape because the best practice is to start small. Transplanting a large oak can be expensive and problematic. Oaks devote most of their early life to developing the root system that will keep them healthy for several hundred years. Large specimens from nurseries have been severely root-pruned to make transplanting possible, but the loss of root structure also makes them more vulnerable to transplant shock. So, starting with a small tree, or even a sprouting acorn, is inexpensive and likely to produce the healthiest tree in the long run. In just a few years, a young sapling will catch up to a severely root-pruned specimen and surprise you with how fast it grows!

Starting a tree from an acorn is fun!
Photo: Alix Dunn
The Oak Circle at the Greenburgh Nature Center just 7 years after planting saplings

So, do this one thing. If transforming an entire landscape to native plants is not an option, consider planting a young oak tree. If you have a lawn, you already have a good spot for the most valuable keystone plant there is. 

Plant an oak tree!

For further information, read the fascinating book The Nature of Oaks by Douglas W. Tallamy

To subscribe to the blog – and nothing else – enter your email below

After the Deluge

If you’ve ever enjoyed the sight of rain drops clinging to every leaf of a tree after a storm, you have observed one of the ways trees manage stormwater. 

Forests intercept rainwater in the tree canopy, and slow its fall to the forest floor where it is absorbed and filtered before any excess gradually moves to streams. A forest can absorb at least 12 inches of precipitation per hour before surface water begins to move toward natural channels. In urban and suburban areas, with limited tree canopy, heavy rainfall hits the ground immediately and accumulates on impermeable surfaces, causing flooding.

Frequent flooding makes stormwater management a top priority

As rainstorms increase in frequency and intensity, flooded roads, neighborhoods, and basements have become critical problems for municipalities and residents. Storm water run-off from impermeable surfaces too often exceeds the capacity of urban and suburban systems. Engineered solutions to flood control are complicated, expensive, and controversial, so urban planners are increasingly considering “green infrastructure” – essentially, managing stormwater by changing how we landscape.

Trees not only remove carbon dioxide from the atmosphere, feed and shelter wildlife, and reduce energy demand for cooling, they are also the most cost-effective way to manage stormwater. Trees and related landscaping can keep excess water off of roadways, and out of your basement.

Trees manage stormwater in several critical ways. If you’ve ever sheltered from rain by moving under a tree, you’ve experienced “interception.” The tree canopy catches rain and holds raindrops on every leaf, twig, stem, and branch until they evaporate after the storm. A mature evergreen can intercept more than 4,000 gallons of rainwater in a year. In a suburban setting, a single deciduous tree intercepts 500 to 760 gallons per year. And a recent experiment demonstrated that even a small flowering tree can intercept 58 gallons of storm water during a ½ inch rain event, or about 67% of the rain that falls on its canopy. Intercepted stormwater never even touches the ground, so it cannot become run-off or cause flooding.

Interception: even in winter, bare tree branches intercept stormwater and hold it for evaporation
The heavily-textured trunks of mature trees slow water down as it falls (“stemflow”) and hold rain until it evaporates

Rainwater that is not intercepted by the canopy and hits the ground is called “throughfall.” Tree roots, which typically spread at least as wide as the tree canopy and are concentrated in the top 18 to 24 inches of soil, break up compacted soil so that more throughfall infiltrates and is absorbed by the ground. Ground water is then taken up by tree roots, transported to the leaves, and used in photosynthesis. That water ultimately is released back into the atmosphere in a process called “evapotranspiration.”

Tree roots absorb water directly and also make soil more absorbent

Trees consume or “transpire” an enormous amount of water. A single mature oak tree can transpire more than 40,000 gallons of water per year! Homeowners who take down mature trees may be shocked to realize that all of that water becomes run-off and a source of flooding when the tree is gone. 

A tree surrounded by pavement or lawn takes up less water than a tree in the forest or a tree accompanied by other plants. Leaf litter, groundcovers, and understory plants dramatically increase the ability of the soil to absorb stormwater. By increasing organic matter and leaf surface under trees, both the amount of stormwater held, and the amount available to the tree for evapotranspiration, are increased significantly.

By contrast, lawn grass is barely more effective than pavement at reducing stormwater run-off. The roots of turf grass are only about 2 inches deep and do not retain much water. Mowing, removing lawn clippings, and using leaf blowers all have the effect of compacting lawn and reducing organic matter in the soil, further reducing its ability to take up water. Automatic irrigation systems, programmed to top-water lawn every couple of days without regard to rainfall, add to run-off problems.

Lawn grass is not effective for stormwater control
The force of stormwater run-off on lawn is even enough to erode paving

Worse, in most communities, storm drains do not channel run-off into sewage treatment facilities, but directly into local waterways, so the chemical fertilizers and pesticides typically applied to lawns are transported by stormwater run-off to our waterways. Pesticides, applied to lawn annually at 10 times the rate used by farmers, are a leading source of water pollution, contaminating groundwater, freshwater streams, rivers, and coastal waters. Lawn fertilizer, washed into storm drains, causes algae blooms and excessive weed growth in waterways.

Storm drains route stormwater directly into streams, rivers, lakes, and the ocean
Stormwater run-off carries toxic pesticides from lawns

Suburban residents can make their yards into “green infrastructure” by reducing lawn and planting densely with native trees and other plants. Parking lots, road medians, church and school grounds, apartment complexes, and any place with lawn or paved surfaces can be added to green infrastructure by planting native trees and landscape plants wherever possible. The best way to prevent stormwater run-off from flooding your basement, blocking your street, and reaching our rivers is to capture it in your own yard with the beautiful trees and plants native to our area.

Dense planting reduces stormwater run-off on a suburban driveway