Drinking water availability patterns amplify domestication of Florida Key deer

• Rain and fresh water lens-filled depressions provide natural drinking water sources for Key deer. • Historically, many natural fresh water sources have been destroyed by human development. • During annual dry season large parts of the deer’s habitat have few or no natural drinking water. • The deer utilize anthropogenic fresh water sources, and are now dependent on them in some areas. • Lack of natural drinking water sources is accelerating domestication of the Key deer. Natural habitat of the endangered Florida Key deer ( Odocoileus virginianus clavium ) is limited to a portion of the lower Florida Keys, large parts of which have been altered by human development. A major reason the deer have survived there is its unique geology that provides surface access to underground freshwater lenses. Such water features provide the deer access to drinking water, however, historically many of the sites have been destroyed through human activity. We examined seasonal drinking water availability to the deer on multiple islands for 3.5 years from April 2019 through September 2022. We also examined the availability of anthropogenic drinking water sources linked to human habitation. Our results show that natural drinking water sources become extremely limited or non-existent during the region’s dry season in large parts of the Key deer range. Anthropogenic freshwater sources in the form of air conditioning drips, garden ponds, water buckets and bird baths are much more numerous, and the deer utilize them regularly. We posit that the existing unavailability of natural drinking water sites is a prime factor driving the domestication of Key deer. This trend of Key deer dependence on humans will only increase as projected increased hurricane activity and sea level rise will negatively affect the freshwater lenses, and hence the number of permanent freshwater sites available to Florida Keys wildlife. The dependence trend could be slowed by management’s readopting natural water source enhancement efforts and installation of water guzzlers as was done in the mid-2000 s but has not been continued since.