Will Defining “Habitat” Put Arizona’s Endangered Species Out To Dry?

By Danika Marzillier.


The Endangered Species Act of 1973 (the “Act”) is one of the United States’ largest pieces of conservation legislation and was enacted with the purpose of protecting vulnerable species and their habitats. Not only does the Endangered Species Act include the designation of vulnerable species as either threatened, endangered, or critically endangered, it also allows the U.S. Fish and Wildlife Service (USFWS) to designate and control areas of critical habitat, thereby preventing further adverse development of the land. Critical habitat is defined under the Act as specific zones within a geographical area occupied by a species that has the physical or biological features which are essential to the conservation of a species and which may require special consideration. It goes further to also consider areas not occupied by the species at the time of their listing, if the Secretary determines that the areas are vital for the conservation of the species.

"Desert tortoise (Gopherus agassizii)" by Joshua Tree National Park is marked with CC PDM 1.0.

However, while “critical habitat” has long been defined by the Act, “habitat” has not. This was recently an issue for the dusky gopher frog when the United States Supreme Court found that in order for something to be declared critical habitat, it must first be considered habitat. The main issue that the Supreme Court was trying to decide in Weyerhouse v. U.S. Fish and Wildlife Service was whether an area that was not currently suitable to be inhabited by the endangered species could be designated as critical habitat. In order to address this gap, the U.S. FWS proposed a definition of “habitat” as well as an alternative definition at the beginning of August and opened the proposed rule to a 30-day public comment period, which ended on September 4, 2020.

The first, and preferred definition, proposed by the U.S. FWS is “the physical places that individuals of a species depend upon to carry out one or more life processes. Habitat includes areas with existing attributes that have the capacity to support individuals of the species.” The second definition is “[t]he physical places that individuals of a species use to carry out one or more life processes. Habitat includes areas where individuals of the species do not presently exist but have the capacity to support such individuals, only where the necessary attributes to support the species presentlyexists.”

While both of these definitions allow for the designation of critical habitat areas where the species is currently not living, but could live, only land that currently has the physical attributes necessary to support an endangered species can be protected. Therefore, land that was historically occupied by a species, or land that could be suitable habitat for a species with restoration, cannot be designated as critical habitat under either definition. This is important because these areas could become vital habitat areas as the planet continues to change in response to climate change and as natural habitat areas become more fragmented due to human urbanization. The most popular example of these effects is coastal areas that will be flooded as sea levels rise, requiring coastal animals to move upland in order to survive. However, Arizona’s hot and dry desert climate and the Southwest’s fast-growing population could make this provision relevant in this state as well.


Arizona could be greatly affected by the definition of habitat chosen by the federal government. The federal government owns 42.29% of the state’s land, while state trust lands make up 12.7 percent. The state also is home to over 44 endangered and threatened animal species, many of which are native and only exist in Arizona’s varied habitats. Some of these species include the bald and golden eagles, the gaguar, the Mexican wolf, and the desert tortoise. At the state level, Arizona currently addresses these issues through the State Wildlife Action Plan, last revised in 2012. Arizona is currently working on addressing species conservation through a new plan, the Arizona Wildlife Conservation Strategy, which will address Species of Greatest Conservation Need and should be completed in 2022. The comment period for this legislation closed on September 15, 2020.

Many challenges face Arizona’s endangered species. Over the past two decades, the climate has become hotter and drier. As many of Arizona’s desert-dwelling creatures are specially adapted to a narrow range of temperatures and conditions, shifts in these conditions can certainly cause the need for species migration or even extinction. Unfortunately, migration is limited due to habitat fragmentation caused by urbanization and development of open landscapes. Further, scientists have noted a trend of homogenization of varied desert landscapes to grasslands, fueled by an increase in wildfires and rising temperatures that increase evaporation, thus resulting in less water being available for biotic communities. Forests and woodlands are predicted to shift upwards in elevation as temperatures rise.

To address this issue, the United States Department of Agriculture has assessed the possibility that it may become necessary to assist in migration, whereby individuals of a species are moved to areas outside of their historic range. Alternatively, it has also been proposed to translocate species to recent historical ranges to lower the risks associated with moving individuals to completely new ranges.

An example of one species being affected by climate change and human infrastructure development is the Sonoran Desert Turtle. Despite its protected status, designated recovery efforts, and regulations, the turtle’s numbers are still declining. While these turtles are highly adapted to high temperatures and drought conditions, the species is threatened on a long-term scale by the increase of water shortages and rising temperatures. One issue facing this iconic creature of the Southwest is human infrastructure blocking their path to relocation, including utility-scale solar arrays, railroads, and highways, making it difficult for the tortoises to migrate to new areas of the desert as their old ranges are or will be experiencing heavy drought. One proposed solution to this problem is the artificial movement of tortoises to regions that could better support them. However, some of these potential areas require restoration before they are appropriate for the tortoises.


This relocation plan is not unique to the desert tortoise. In fact, many species are expected to shift their current ranges to more accommodating areas as the climate changes, either naturally or via artificial relocation. However, this will be much more difficult if the current proposed definition of habitat is accepted. As scientists predict changing climates over the next few decades and as human populations continue to grow and urbanize, we will need to make decisions regarding what we want to do to address a reduction in habitats and natural areas. The Endangered Species Act itself is hotly contested, as support and criticisms are widespread and range from the Act overstepping and going too far on one hand to arguing that it does not go far enough to protect species on the other. The unfortunate reality is that adaptation may be difficult, and state and federal legislatures will need to decide how much to intervene and where to draw the line.