Deer population must be managed to protect ecosystems

Healthy ecosystems rely on checks and balances among all species, plant and animal alike.

Foxes prey on smaller animals like mice, squirrels, snakes and amphibians. In turn, amphibians such as frogs consume insects, worms and even small fish. These interactions occur across every ecosystem and explain how energy moves through the food web. They also allow ecosystems to remain resilient, genetically diverse and functional over time.

When a species is lost, especially a keystone species, ecosystems begin to unravel. With white-tailed deer, we are seeing this clearly happen in Delaware and across much of the country. Historically, wolves and other large predators kept deer populations in check at sustainable levels. Without these predators, the only remaining controls on deer populations are vehicles and hunters.

Current deer populations across Delaware often exceed 100 to 150 per square mile. Ecologically sustainable levels are closer to 10 to 15 per square mile, meaning 10 to 15 times higher than what our forests can sustain.

Why does deer overpopulation matter, and what does it mean for ecosystems?

Deer prefer to eat native plants. In forest ecosystems, this prevents regeneration because they’re consuming seedlings and young plants faster than they can recover, leading to collapse of native plant communities.

This matters because native plants form the foundation of terrestrial food webs. Roughly 90% of insect species rely on specific native plant species or plant families to reproduce. When native plants disappear, the insects that depend on them disappear as well.

North America is home to roughly 14,000 species of butterflies and moths, many of which are highly specialized. No milkweed means no monarch butterflies. No pawpaw means no zebra swallowtails. The loss of native plants cascades quickly through the ecosystem.

Insects are the most efficient way to move energy through a food web. When native plants decline, insect populations collapse, and when insects disappear, the entire system begins to fail.

Some 96% of bird species feed their young insects, especially caterpillars, rather than seeds or berries. Freshwater fish depend on aquatic insects. Amphibians, foxes and bears all rely on insects directly or indirectly. Even animals that do not consume insects depend on prey species that do.

Healthy forests clean and store water, capture carbon, reduce erosion and produce the oxygen we breathe. Forests depend on insects for pollination and nutrient cycling. Without insect pollination, new trees fail to replace aging ones, which perpetuates a vicious cycle of ecosystem collapse.

Since the early 1970s, insect populations have declined by roughly 45%, and North America has lost nearly 3 billion birds.

So how does this implicate deer? The last time deer populations were near ecological balance was also in the early 1970s. These declines are interconnected, and without action, they will worsen.

At current deer population levels, this entire system is under threat. Forest understories are being eaten faster than they can regenerate. Native plants are eliminated before they can mature. What remains is open space vulnerable to invasion.

Invasive plants exploit these gaps. Studies show that deer tend to prefer native plants and avoid many invasive species altogether, giving the invading flora a competitive advantage where native plants have been eliminated.

To be invasive, a species must be non-native, often introduced from other world regions, and cause or be likely to cause ecological harm, economic harm, or harm to human health. Many invasive plants originated in landscaping, including Japanese barberry, Japanese pachysandra, Burning Bush/European privet, and Callery pear. These plants produce little to no usable food for native insects because insects require thousands of years to adapt to a plant’s chemical defenses, not the few decades most invasive species have existed here.

As a result, our forests are failing to regenerate. Young maples, oaks, hickories, viburnums and hemlocks are scarce or absent. In their place, invasive species have overtaken large swaths of land. Without intervention, the forests will continue to degrade into resource-scarce monocultures dominated by invasive species. 

This is not a distant problem. It is happening locally, in places we know and visit. 

Cape Henlopen State Park is constantly being inundated by invasive species from surrounding private properties, in addition to the 50,000 invasive Japanese black pines planted during World War ll. Park management is tirelessly working to reduce and eliminate ecologically useless invasive species within its 5,450 acres, but these efforts are made less effective by the park’s overpopulation of deer. 

The consequences extend beyond ecosystems. Deer cause hundreds of millions of dollars in crop damage annually. Vehicle collisions involving deer kill hundreds of people each year and result in billions of dollars in damages. High deer densities also contribute to the spread of Lyme disease and destroy billions of dollars’ worth of residential landscaping. The ecological costs and human costs are inseparable.

Delaware must address deer overpopulation directly. Regulated hunting is one of the few effective tools remaining, and it plays a critical role in population management. Hunters are not adversaries of conservation; they are participants in it. At unsustainable population levels, inaction does not spare deer from harm. It leads to widespread starvation, disease and prolonged suffering within deer herds, while accelerating the loss of insects, birds and other wildlife that depend on intact native plant communities.

If we want more birds, more wildlife, healthier forests, fewer vehicle collisions and reduced disease risk, deer populations must be managed.

This is an uncomfortable reality, but avoiding it will not protect ecosystems. If we want a sustainable and resilient future, we must confront this issue directly.

The buck stops here.