Birds can cause significant damage to plants in a variety of ways. Their feeding behaviors, waste elimination, nesting habits, and other activities can harm plants both directly and indirectly. Understanding how birds interact with vegetation can help gardeners and land managers prevent or mitigate bird damage.
Direct Physical Damage from Feeding
Many types of birds directly consume parts of plants as they forage. While most bird species mainly eat insects, berries, seeds, or nectar, some are more destructive feeders that can ravage fruits, flowers, buds, leaves, stems, roots, and seeds of desired plants.
Some examples of bird species that can physically damage plants include:
- Sparrows – Feed on seeds, seedlings, buds, fruits
- Finches – Feed on flower buds, fruits, seeds
- Crows – Will eat seeds, fruits, seedlings, grains and other crops
- Blackbirds – Feed on buds, fruits like berries, seeds, and grains
- Starlings – Eat fruits like grapes and berries as well as grains, buds, sprouts
- Pigeons – Feed on seeds, grains, sprouts, greens
These birds and many others can directly damage fruits like grapes, berries, melons, and citrus by pecking holes in ripe produce to get at the juicy interior. They may remove strawberry caps, eat the outside of corn kernels, or strip flesh from developing peaches or cherries.
Birds also commonly feed on newly sprouting seeds and seedlings, destroying them right after planting. They dig up germinating seeds like beans, pull up sprouts of lettuce and other greens, and nibble off young growth on vegetables. This can set crop plants back significantly.
Buds ready to open into flowers or leaves are another prime target. Birds like finches can pinch off buds before they have a chance to develop. Removal of too many buds negatively impacts fruit and vegetable yields.
Grains like rice, wheat, sorghum, and corn are susceptible to bird damage both before and after harvest. Flocks of blackbirds, starlings, sparrows, and pigeons will descend on fields and feed on ripening grains right on the stalks. Post-harvest, these birds still raid storage facilities and leftovers in fields for their carbohydrate-rich bounty.
Fouling by Waste
Bird droppings are rich in nitrogen, composed of a mixture of fecal and uric acid. This nutrient-dense waste certainly helps fertilize landscapes. However, excessive bird feces can burn and discolor plant leaves and fruits. The high nitrogen concentration can even damage plants by forcing succulent growth vulnerable to disease.
Fruit crops like grapes, berries, and orchard fruits are especially at risk of damage from bird feces. Droppings on sweet fruits can ruin their aesthetic appeal. But more importantly, bird waste can spread dangerous pathogens like E. coli, salmonella, and toxoplasma. This food safety threat means any fruits with bird feces may be unfit for human consumption.
Bird droppings can also accumulate under roosting or nesting spots in high enough levels to injure vegetation. Evergreen trees and shrubs are particularly prone since birds perch on them year-round.
English ivy, boxwoods, yews, arborvitae, and other landscape plants under bird roosts often develop discolored, withered leaves and damaged growth. The nitrogen overload and contamination essentially burns the plants.
Destruction from Nesting Materials
Birds rely on readily available plant parts like leaves, stems, roots, and twigs to assemble nests. While utilizing dead brown materials strewn on the ground has minimal impact, birds often favor fresh, flexible green plant growth.
Robbing too many living leaves, needles, twigs or vines from a single plant or shrub can stunt its growth. Birds like crows and jays pluck long strips of bark from trees, damaging the cambium layer that transports nutrients.
Nests built directly in shrubs or trees also increase local damage. The large, frequent structures of colonial nesters like herons and cormorants break branches and strip areas of foliage.
Some birds even make use of lawn thatch for nest warmth and stability. Ripping up pieces of sod weakens grass, creating dead patches.
Methods to Prevent and Deter Bird Damage
A variety of deterrents and management strategies can limit the harm birds inflict on landscaping and crops. The most effective plans incorporate multiple techniques.
Physical Barriers
Physical exclusion of birds is the most direct way to protect plants. Netting over fruit crops, vegetable gardens, or nursery plants creates an impenetrable barrier against feeding. Small mesh netting with openings less than a half-inch can exclude most birds.
For crops like berries or orchard fruits, cover plants with netting before the first signs of ripening. Prompt removal of the nets after harvest also deters damage. Making sure to secure edges of netting prevents gaps where determined birds can enter.
Bird netting over ponds and other open water sources likewise prevents access that attracts birds to adjacent plantings. Overhead grid wires or parallel monofilament lines can also discourage birds from landing.
Wrapping tree trunks in burlap, window screening, or plastic spiral guards prevents bark stripping. Use plastic or mylar tape, old CDs, or similar reflective deterrents to repel birds from ripening fruits or gardens. Attach these sparkly items to stems and branches with twist ties.
Chemical Repellents
Non-toxic chemical taste or odor repellents may discourage bird feeding on certain plants. Capsaicin-based compounds added to liquid repellents create a spicy, peppery taste. Other products include bittering agents or volatile chemicals with disagreeable smells.
Repellents work best before birds develop set feeding patterns. Begin applications at the first sign of ripening fruit or vulnerable new growth. Reapply every 7-10 days according to product instructions. Rainfall, irrigation, or wind will dissipate active ingredients.
While chemical bird repellents likely won’t deter all birds or provide full season protection, they can provide supplemental damage reduction. Target them for high-value fruits, newly seeded beds, or nursery stock.
Scare Devices
Strategic use of scare devices that produce startling sounds, flashes, or threatening movements can frighten away problem bird species. These work by triggering birds’ instinctive fear reactions.
Propane-powered cannons create intermittent explosions to scare birds. Though loud and stressful for humans, cannons used for short periods at key times deter flocking birds. Mixing propane cannon use with occasional shooting of wildlife safe cracker shells or bird bombs from a starting pistol maximizes the frightening effects.
Visual scare devices include shimmering deterrent tapes, balloons with large eye spots, and flashing lights. Strategic placement in affected areas only as needed reduces habituation. Motion-activated sprinklers likewise briefly startle birds with a spray of water when they enter the range. For nighttime roosts, spotlight beams triggered by motion detectors also work.
With all scare devices, birds will become accustomed to continuous operation. Varying the location, timing, and type used prevents complacency.
Population Management
In areas with extensive agricultural plantings or managed gardens, the density of problem bird species may outstrip other control methods. Where allowed by law, reducing local populations through trapping or hunting can improve results.
Special permits allow capturing of birds like European starlings and house sparrows identified as crop pests. Consultation with USDA Wildlife Services or local agencies provides guidance on lawful trapping.
Hunting opportunities for species like crows, blackbirds, and pigeons may also be an option on appropriate private properties or rural lands outside municipal boundaries.
Important Considerations
When planning and implementing bird damage management strategies:
- Properly identify contributing birds and the type of damage occurring.
- Time deterrents and harassment to the earliest signs of bird activity.
- Combine multiple techniques for better effectiveness.
- Adapt plans annually based on results.
- Ensure compliance with all laws and regulations.
- Avoid harming protected bird species.
Impact of Birds on Plants
Birds can positively influence plant communities through seed dispersal and pollination. However, detrimental impacts often necessitate control measures in managed agricultural, ornamental, and natural settings. Understanding the interactions between birds and plants helps strike the right balance.
Though birds damage a wide variety of plants, a few examples illustrate their typical effects:
Grapes
Grapes are highly susceptible to bird damage, especially ripening table grapes. The skins are thin with a sweet, juicy pulp that birds relish. Starlings, robins, finches, crows, and other species peck grapes directly off vines from veraison (onset of ripening) through harvest. The holes and juice stains left make clusters unmarketable.
Bird damage frequently reaches 25% or more of the overall crop, sometimes exceeding 80%. Financial losses are measured in the tens of millions per year for some tart cherry, berry, and grape growing regions.
Blueberries
Many bird species pluck and feed on ripening blueberries, opening up wounds that lead to decay. Starlings, grackles, robins, and crows cause the majority of damage.
Research showed bird damage reduced blueberry yields by 13-26% in New Jersey. Missing fruits also resulted in more concentrated loads of parasites and pathogens on remaining berries.
Lettuce
Birds like crows and geese pull newly germinated lettuce seedlings right out of the ground as they scavenge for seeds or greens. Poking around soil often also uproots tiny vegetable seedlings. Replanting and delayed maturity result.
One California study documented 74% loss of lettuce seedlings to bird predation after planting. Significant reductions to yields continue as flocks feed on emerging and maturing lettuce heads.
Sunflowers
While feeding damage from birds is not an issue for commercial hybrid oilseed sunflower crops, it seriously impacts confectionary varieties. These types have large seeds lacking hulls that birds consume right from the flower heads.
Goldfinches in particular flock to fields of confectionary sunflowers, devastating yields. Losses over 80% are typical if controls are not implemented.
Conclusion
Birds fill important niches in ecosystems, but sometimes necessitate control and management in human-altered settings. A variety of techniques can reduce damage from feeding, waste, nesting, and other bird behaviors in crops, gardens, and nurseries. An integrated plan tailored to the species and plants involved provides the best results.
Understanding both avian nature and the vulnerability of desired vegetation enables coexistence. With some tolerance for minor damage and use of preventive measures only as needed, birds and plants can thrive together.