English ivy (Hedera helix) is a familiar sight, often used as an evergreen ground cover or climbing vine. Its aggressive growth habit and ability to thrive in various conditions have made it an increasingly common plant, often bordering on invasive in North America. White-tailed deer populations have expanded and adapted to these environments, leading to frequent encounters between the animals and cultivated plants. The question of whether deer consume English ivy arises from the conflict between landscape preservation and the deer’s need for forage.
Palatability and Preferred Forage
Deer are highly selective browsers, classified as “concentrate selectors,” meaning they prioritize consuming the most nutrient-dense and easily digestible plant parts. Their preferred diet consists of tender shoots of woody plants, soft leaves, and forbs—broad-leaved herbaceous plants that offer high levels of crude protein and phosphorus. These choices are driven by the deer’s small, specialized rumens, which require easily fermentable material for efficient digestion.
English ivy, with its tough, leathery, and waxy leaves, generally falls low on this preference hierarchy, offering low nutritional value for a selective browser. Palatability varies by region and season, and consumption often reflects a lack of better options rather than a universal preference. The evergreen nature of ivy means it retains foliage when many other plants have died back, making it a visible food source.
Chemical Deterrents and Toxicity
The primary reason deer tend to avoid English ivy is the presence of defensive chemical compounds that make the plant taste bitter and potentially toxic. The most significant of these are triterpene saponins, specifically hederacoside C and alpha-hederin, which are concentrated in the leaves and berries. Saponins are glycosides that serve as a natural deterrent against herbivores.
When consumed, these saponins can cause severe irritation to the mucous membranes lining the deer’s digestive tract. In non-ruminants, consumption can lead to symptoms like vomiting and diarrhea; in deer, it is thought to disrupt the delicate balance of the rumen’s microbial population. English ivy also contains polyacetylene compounds that can cause contact dermatitis in mammals. The combination of these bitter-tasting and irritating substances makes the plant unappealing, discouraging the deer from consuming large quantities.
Environmental Stress and Browsing Behavior
The instances where deer browse English ivy are usually situational, overriding their natural aversion to the plant’s deterrents. This behavior is most commonly observed during periods of environmental stress when preferred, high-quality forage is scarce. Severe winter weather, deep snow cover, or extended drought conditions can limit access to tender forbs and woody browse, forcing deer to consider less palatable alternatives.
When faced with starvation, deer will resort to browsing on any available green material, including ivy. In areas with high deer population density, competition for food also increases the likelihood of ivy consumption. Browsing typically involves taking small bites or nibbling on the youngest, least-waxy leaves or shoots. While English ivy is not a staple of a deer’s diet, it serves as a “backup” food source consumed out of necessity when environmental conditions leave few other options.