In , Neotropic Cormorants prefer fresh water lakes, ponds, lagoons, and slow moving rivers containing large densities of fish with available trees, snags, islands, or open banks for loafing. In the species has become common to locally abundant in some urban lakes and ponds in the greater area, as well as along perennial sections of the lower Salt and Gila rivers downstream to Gillespie Dam. Several concentration areas have already exceeded 500 individuals (figure 3). The highest densities have been observed at several residential lakes in and Gilbert, just upstream of , and several gravel extraction company lakes on the Salt and . However, it should be noted that the specific concentration locations are often temporary and are based on abundant populations of appropriate size fish. Once prey populations are reduced, these highly mobile cormorants readily move to other neighborhood lakes and ponds.
The environmental factors that have influenced the exponential increase in populations of Neotropic Cormorants and stimulated their northern range expansion are unclear. More research is needed to determine the precise reasons of these changes, which are likely due to an increase in available foraging and nesting sites (Telfair and Morrison 2005). Specifically in , the rapid cormorant population growth in the area has certainly been influenced by an increase in available prey at urban ponds, canals, and man-made lakes. At least four species of exotic tropical fish ( spp.) have been introduced into and are frequent prey items of both Neotropic and Double-crested Cormorants. Although the practice is discouraged by the Arizona Game and Fish Department, private property owners and lake managers continue to release in an effort to control the growth of certain aquatic plants (E. Swanson, personal communication). are prolific breeders and they can mature and begin reproducing at only six months of age, thus providing a plentiful supply of appropriate size prey for cormorants throughout the year. Unfortunately birds also consume other types of preys and the rapid increase of cormorants in the area is becoming a serious challenge and financial burden to those that stock game fish into urban lakes and ponds for fishing. Recent discussions have begun that may lead to attempts at locally controlling cormorant numbers in some urban areas.
The proposed genus appears to be - the European species have been separated in , and the North American ones are placed in the expanded . A fossil cormoran foot from (Germany), sometimes placed herein, would then be referable to if it proves not to be too distinct. All these early European species might belong to the basal group of "microcormorants", as they conform with them in size and seem to have inhabited the same habitat: subtropical coastal or inland waters. , meanwhile, was initially believed to be a or a by some. There are also undescribed remains of apparent cormorants from the of (), dating to some time between the and the mid-.