Since the ceding of the Panamá Canal from the United States to the Republic of Panamá in 1999, human development has accelerated, resulting in the loss of tropical rainforest habitat and declines in wildlife populations. In 2007 this area of vast plant and wildlife diversity experience further loss of habitat as land clearing and excavation commenced for the Panamá Canal Third Locks Expansion Project. As one of the largest construction projects in the world, the potential impacts of the expansion prompted the Panama Canal Authority to work with a local non-governmental conservation organization to initiate a wildlife rescue and relocation operation to conserve wildlife in the affected areas. From 2007 to 2010, 896 wildlife rescue events occurred in 11 areas along the Canal; 806 of these individuals (90%) were successfully relocated to protected areas (n=749) or captivity (n=57). These wildlife rescue efforts were summarized, including human labor required, wildlife species composition, and conservation statuses according to the IUCN and CITES. Also quantified were wildlife dominance and biodiversity using the Simpson, Shannon, Berger-Parker, and Brillouin diversity indices, relative abundance of >100 Neotropical species, and habitat-abundance relationships for four focal species: Hoffman's two-toed sloth, Choloepus hoffmanni; brown-throated three-toed sloth, Bradypus variegatus; American crocodile, Crocodylus acutus; and common caiman, Caiman crocodilus. Relationships between diversity indices and habitat for the wildlife rescued during the wildlife rescue project were also analyzed. Results indicate the Panamá Canal Watershed to ii possess a diverse representation of Neotropical wildlife. Habitat-abundance relationships of focal species suggest two-toed sloth numbers increased as the edge of secondary forest decreased and number of three-toed sloths increased as total landscape area of agriculture decreased. Crocodile populations increased as number of patches on the landscape and mean patch size of secondary forest decreased, and caiman numbers increased as the edge density of secondary forests decreased and mean patch size of agriculture increased. Diversity-habitat relationships revealed wildlife diversity increased with heterogeneous secondary forest landscape consisting of less edge. This project provides rare insights into wildlife rescue operations and wildlife-habitat relationships for Neotropical wildlife species that will be useful for a range of conservation efforts. Additionally, this research provides updated population assessments for many of the species included in the research, especially the focal species, in which a need for them has been stressed in the conservation literature.

The field of wildlife rescue and rehabilitation continues to grow as human expansion increases the rate of deforestation in Latin America. Wild animals that are often rescued from becoming orphaned or injured are rehabilitated in captivity until considered suitable for release back into the wild. Sloths (Bradypus spp. and Choloepus spp.) are a common species admitted to rescue centers throughout Latin America due to their poor dispersal abilities and vulnerability to anthropogenic impacts. Post-release monitoring is fundamental in measuring the success of wildlife rescue programs, however, few studies have assessed the outcomes of releasing hand-reared sloths back into the wild. I studied the ecology of rehabilitated and relocated Hoffmann’s two-toed sloths (C. hoffmanni) in central Panamá. My objectives were to: (1) use a soft-release technique to quantify activity budgets of individuals prior to release in the wild, (2) analyze movement trajectories and estimate home range sizes, (3) assess habitat selection, and (4) determine survival rates and causes of mortality for rehabilitated and released two-toed sloths. Eleven two-toed sloths rescued from the wild were hand-reared in captivity for a mean total of 727  193 days (mean  SE value across all sloths) at the Pan-American Conservation Association facilities in Colón Province, Panamá. During 2019-2020, sloths were processed into 2 groups, radiomarked, placed in an outdoor 500 m2 soft-release enclosure for 3 months, and released in nearby Soberanía National Park. I conducted 580 hr of behavioral observations during soft-release to quantify activity budgets for 5 main activity states. A linear mixed model was used to compare two-toed sloth activity budgets in response to sex, age, season (i.e., dry vs. wet), session time (i.e., morning vs. evening) and month. Rehabilitated two-toed sloths spent 80.0% of their time resting, becoming active and more alert in the evening, exhibiting behavioral patterns similar to wild two-toed sloths (as ascertained from existing literature). I used homing to radiotrack two-toed sloths for 210 radio-days during which I used a paired analysis approach to measure tree height, crown height, height to crown base, diameter at breast height, abundance of lianas, canopy depth, and canopy closure at 118 used and random locations. Habitat selection was modeled using conditional logistic regression and movement trajectories were analyzed using ArcGIS. Rehabilitated two-toed sloths traveled shorter distances than wild two-toed sloths, traveling a mean linear distance of 82.3  21.6 m and a mean distance of 25.6  9.5 m between successive locations. Mean home range size for released two-toed sloths was 2.92  1.19 ha with females occupying larger areas than males. I did not find strong evidence of habitat selection; however, rehabilitated two-toed sloths chose trees with a smaller dbh than available. Habitats used by rehabilitated two-toed sloths closely resembled those used by wild two-toed sloths, selecting trees with dense crowns and 50% lianas. Monthly survival for rehabilitated two-toed sloths (0.72  0.14) was low relative to wild sloths, and monthly estimates for males (1.00  0.00) and females (0.44  0.22) did not differ (P  0.30). Eight mortalities were recorded with predation and natural causes being the main causes of mortality. My study provides information that can be useful in evaluating the costs and benefits of sloth rescue and rehabilitation programs throughout Latin America.

Despite the restricted morphology and distribution of sloths today, fossils sloths show a wide variety of forms and behaviors and used to range from South America to Alaska. These extinct forms have in the past simply been lumped together as "ground sloths", separated from modern "tree sloths". However there are intermediate forms that have been posited to be semi-arboreal. In other groups such as primates the shape of the shoulder blade has been shown to vary significantly between groups with different arboreal behaviors. This study used geometric morphometrics to examine the scapulae of modern and extinct sloths to show that these three locomotor groups can in fact be distinguished by their shoulder blade shape. Juveniles of giant ground sloths also have significantly different shoulder blade shapes than the much larger adults, however they do not overlap with the smaller intermediate sloths, so may have been just as terrestrial as their parents despite their much smaller size. Finally, ontogenetic trajectories of several sloth genera do not show evidence of having different slopes. They start and end in different areas of morhospace but are all on parallel paths. This argues against the hypothesis of convergence in modern tree sloths, which despite both having an unusual suspensory lifestyle are not closely related. Rather they are both retaining an ancestral growth trajectory that all sloths have possessed.

Living sloths represent two distinct lineages of small-sized mammals that independently evolved arboreality from terrestrial ancestors. The six extant species are the survivors of an evolutionary radiation marked by the extinction of large terrestrial forms at the end of the Quaternary. Until now, sloth evolutionary history has mainly been reconstructed from phylogenetic analyses of morphological characters. Here, we used ancient DNA methods to successfully sequence 10 extinct sloth mitogenomes encompassing all major lineages. This includes the iconic continental ground sloths Megatherium, Megalonyx, Mylodon, and Nothrotheriops and the smaller endemic Caribbean sloths Parocnus and Acratocnus. Phylogenetic analyses identify eight distinct lineages grouped in three well-supported clades, whose interrelationships are markedly incongruent with the currently accepted morphological topology. We show that recently extinct Caribbean sloths have a single origin but comprise two highly divergent lineages that are not directly related to living two-fingered sloths, which instead group with Mylodon. Moreover, living three-fingered sloths do not represent the sister group to all other sloths but are nested within a clade of extinct ground sloths including Megatherium, Megalonyx, and Nothrotheriops. Molecular dating also reveals that the eight newly recognized sloth families all originated between 36 and 28 million years ago (mya). The early divergence of recently extinct Caribbean sloths around 35 mya is consistent with the debated GAARlandia hypothesis postulating the existence at that time of a biogeographic connection between northern South America and the Greater Antilles. This new molecular phylogeny has major implications for reinterpreting sloth morphological evolution, biogeography, and diversification history. Extant sloths are the survivors of an evolutionary radiation marked by the extinction of large terrestrial forms of the Ice Age. By sequencing ten mitogenomes from extinct sloths, Delsuc et al. present a new molecular phylogeny revealing widespread morphological convergence with major implications for reinterpreting sloth evolutionary history.

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