Key deer eat more than 160 species of plants. The 2 most important are mangrove trees and thatch palm berries.  They are perfectly adapted to thrive on native vegetation.    They have very delicate gastrointestinal systems and that is one of several important reasons they should not be fed.

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It’s no problem for this Key deer doe to stand on hind legs to reach desired vegetation.

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Key Deer buck eating Black Mangrove.

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A group of young Key deer led by a collared doe foraging on Red Mangrove.

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Key Deer doe stripping off Thatch Palm berries during summer.

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Toro munching on Red Mangrove leaves. He spends most of his time foraging and resting. Non-native vegetation and “human” food may severely upset his digestion.

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Key deer doe eating grass.

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Key deer doe eating Thatch palm flowers.

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Key deer doe eating Dogwood.

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Key deer doe eating mushroom.

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Young Key deer buck eating Red mangrove.

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Key deer doe eating Gumbo limbo.

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Key deer doe eating Green buttonwood.

Key deer doe eating Batis.

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Key deer doe eating Bay Cedar.

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Key Deer buck eating algae.

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Key Deer doe eating grass.

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Key Deer Button Buck eating Red Mangrove propagule.

Key Deer Buck eating Thatch Palm berries.

What Do Key Deer Eat?

While many of you may respond to our question jokingly with “What don’t they eat?”, you may be surprised to learn that due to their isolation in the Keys, Key deer actually have quite a specialized diet. Scientific studies started back in the mid-1950s when there were just a few dozen Key deer left after surviving poachers. Direct observations recorded “at least 21 plants”. Remember that in those days very few people lived in the Keys and the few remaining deer had little, if any, contact with residents. A 1955 study using observations and poop pellet analysis concluded that “more than 63% of the studied deer had red mangrove as a major part of their diet.”

Fast forward to 1990s and mid-2000s, when interest in Key deer contributed to regular scientific research  (since then, federally sanctioned Key deer research has  ground to a near-halt through today). Much habitat changed between the 50s and 90s due to the huge onslaught of humans and their non-native plants invading the Keys. In 1990, Dr. Klimstra, the Key deer guru at the time, utilized rumen (deer stomach) samples from 129 Key deer killed by cars on Big Pine, No Name, Little Torch, and Big Torch to determine a Key deer’s average diet. His findings: a mere 10 plant species comprised 56.6% of everything the Key deer decided to eat. More than 24% of their diet was red or black mangrove (same as in the 50s)! Indian mulberry and silver palm and thatch palm flowers and fruits pretty much covered the rest. So as far as we can tell, our present Key deer continue to follow their 50’s ancestor’s diet (see photo). Mangroves are not on the menu of mainland whitetails but are obviously vital to Key deer. As was published in 2020 by an SOKD Board member in a peer-review science journal, Hurricane Irma destroyed more than 25% of mangroves on some islands, thus reducing the deer’s major food supply. The loss is still quite noticeable in some areas.

So besides mangroves and the other traditional plants, what else do Key deer eat? Just about anything natural in their habitat, since their island resources are often sparse.  We have seen a Key deer work very hard to jump up under an osprey nest to get at a dead fish dropped in the bushes from the nest – a rather unique situation illustrating how opportunistic Key deer can be in their food choice. And that presents a problem: Klimstra’s study found over 150 different plants consumed by Key deer, perhaps including carrots and lettuce from the local, well-meaning residents. While still unlawful, small amounts of veggie snacks or landscape clippings likely don’t hurt the deer, but other non-native, high-carb foods do – and have actually killed Key deer. Even carrots, which are full of sugar, can cause problems in quantity. Corn in any form including raw, cracked, chips etc. as well as bread, pizza, rice, cookies – any foods high in simple carbs can kill Key deer. Here’s why: Unlike people and mainland deer that have some long-term contact with hi-carb foods, (think corn fields, hunter bait stations, etc.), Key deer generally don’t get such extreme access to high carb caches. When they do all of a sudden, they don’t know any better and gorge on the stuff…and they get very sick due to a rapid change in bacteria in their stomachs that turn it acid (“rumen acidosis” or “bloat”), and in extreme cases die a painful death (we’ve witnessed it) that is unavoidable once overt symptoms set-in. SOKD has made it one of its primary goals to educate residents and especially the tourist industry through many participating Keys businesses about the Key deer diet threat, having distributed over the past 5 years close to 80,000 educational brochures throughout the Keys at a cost of many thousands of dollars. We are happy to report that the campaign has received great feedback and has hopefully had some effect: the number of Key deer rumen acidosis cases that we are aware of have definitely decreased in the past 2-3 years from the previous years. So, help us tell the tourists to stop feeding our deer doughnuts or other people crap – because by the time they are sharing their phone shots with friends back on the mainland, that buck they let gorge on their left-over pizza outside a BPK restaurant (unfortunate, true story)…was dead from rumen acidosis. To learn more about the deer and our organization, please visit www.saveourkeydeer.org .