Discussion
We compiled a large dataset that describes mortality due to
wildlife-vehicle collision in Ecuador based on both systematic surveys
and non-systematic records that came from citizen science and
opportunistic observations reported in the scientific literature.
Collectively, these data reveal that 13.66% of described vertebrate
species from Ecuador are susceptible to die on roads, a number that
likely underestimates the true impact of roads as not all areas are well
sampled and smaller and cryptic species may be underreported. We see a
need for additional systematic surveys, which can provide more
comparable estimates, and have been few and limited to some areas.
Likewise, citizen science reports are overrepresenting certain areas,
with gaps in other regions.
We found that marsupials (D. marsupialis , and D. pernigra )
represented more than a half of mammalian records (systematic and
non-systematic) reported in 21 out of the 24 provinces. Their generalist
habits (diet and habitat), together with increased abundance and
intermediate body masses could be important factors for their high
mortality (Medrano-Vizcaíno et al. , 2022). Likewise, species with
a scavenger or omnivorous diet such as the American black vultureCoragyps atratus, the smooth-billed ani Crotophaga ani and
the groove-billed ani Crotophaga sulcirostris comprised a great
part of the avian records. The common green iguana Iguana iguanawas the most common roadkilled reptile. While this is mainly a
herbivore, iguanas have been recorded feeding on carcasses of deer and
opossums (Anderson & Enge, 2012). Roadkilled animals and invertebrates
that get attracted to these carcasses can be a food source for
scavengers, which attracted to road then have a higher probability of
being hit by a car.
Among the systematic studies we estimated particularly high standardized
mortality rates in some cases. Studies in Galápagos (García-Carrascoet al. , 2020), Napo (Filius et al. , 2020), and Manabí
(Gaón & Valdez, 2021) where roadkill rates were disproportionally high
in comparison with other studies were all conducted in small areas
(13.8, 15.8, and 10 km, respectively). These areas could be hotspots of
mortality that do not represent rates across wider areas (overestimate
risk). On the other hand, roads in these studies were surveyed by
bicycle. Slower survey methods like bicycle or walking can result in
higher detectability, 8.4 times higher than using a car (Wang et
al. , 2022). Therefore, these studies may be better capturing the true
mortality, at least for those smaller areas.
How road impacts wildlife in areas of biological importance should be
further studied. For example high road mortality for endemics of the
Galápagos Islands could threaten population persistence (Wiedenfeld,
2006; Tejera et al. , 2018). In this territory, threatened species
comprise 20 out of 43 birds species, 18 out of 42 reptiles species, and
6 out of 9 non-cetacean mammals species (IUCN, 2022), for which the
impacts of roads on their populations remain unexplored. But also
non-threatened species may be impacted. For example, the yellow warblerSetophaga petechia , that was commonly reported as roadkill, has
experienced a dramatic population decline, and although low insect
abundance due to intense use of herbicides has been associated with this
decline (Dvorak et al. , 2012), road mortality could contribute to
further declines (or already be a factor). While there have been two
systematic studies in Galápagos these offer limited insight as one
focused on a single species focus (Tanner & Perry, 2007) and the other
represented a single one-month survey (García-Carrasco et al. ,
2020). The real impact of roads on wildlife populations in Galápagos
remains unknown and considering the high endemism and quantity of
threatened species, we think that this area deserves special attention
for research.
We found roadkill records for 15 Threatened and six Data Deficient
species, with some of them showing repeatedly in different regions of
Ecuador. The Peters’ running snake Coniophanes dromiciformis , is
a Vulnerable and little known species recorded in only nine locations of
Ecuador (Cisneros-Heredia, 2021). This range-restricted species showed a
roadkill rate of 1.19 ind./km/year in Manabí, with an additional four
non-systematic records. Another worrying case is the Violet-throated
Metaltail Metallura baroni . This bird, catalogued as Endangered
and endemic to Azuay and Cañar provinces, is known from five locations
(BirdLife International, 2016), and we estimated roadkill mortality of
0.13 ind./km/year in Azuay, with an additional non-systematic record. In
addition, we gathered seven non-systematic records of the pacific horned
frog Ceratophrys stolzmanni in Manabí, a Vulnerable and
rare species whose entire population is distributed in less than eight
subpopulations (IUCN SSC Amphibian Specialist Group, 2018). Directing
research efforts on roads within the distribution areas of these
range-restricted species could be important to determine the impact of
roads on their populations.
Additionally, poorly studied organisms such as Caecilians andAtractus sp. snakes were also regularly reported as roadkill.
These animals are among the least known vertebrates, with several
taxonomic uncertainties and unknown conservation status for many of them
(Cisneros-Heredia, 2005; Wilkinson, 2012; IUCN, 2022). Both groups were
frequently detected across three studies in Napo (Filius et al., 2020;
Medrano-Vizcaíno & Espinosa, 2021; Medrano-Vizcaíno et al. in prep),
and non-systematic data included 41 records of Atractus sp.
snakes. In a survey conducted in 2014, Medrano-Vizcaíno & Espinosa
(2021), found two roadkilled individuals attributed to the genusAtractus in Napo that were latter described as new species
(described by Melo-Sampaio et al., 2021; Arteaga et al., 2022). Road
ecology research in areas with poorly-known and undescribed species
would be valuable, both to quantify impacts but also to potential expand
our understanding of these species.
Our study offers an overview of wildlife mortality on Ecuadorian roads,
but likely underestimates the impact. We obtained roadkill records from
all the 24 provinces in Ecuador, but systematic studies were only
available for five, and non-systematic data was disproportionally
distributed in provinces like Manabí, and Napo (more than 300 records
for each province). While in Bolívar, Cañar, Carchi, Cotopaxi,
Galápagos, Los Ríos, Pastaza, Santa Elena, and Zamora Chinchipe, we
gathered less than ten records per province. Our results also show that
citizen science data can complement systematic studies and identify top
roadkill species (like D. marsupialis, D. pernigra, S. petechia ,
and R. marina ) that were both commonly reported in non-systematic
and systematic data from Galápagos, Manabí, Guayas and Napo (González,
2018; Filius et al. , 2020; García-Carrasco et al. , 2020;
Zavala, 2020; Gaón & Valdez, 2021; Medrano-Vizcaíno & Espinosa, 2021).
We hope by expanding our network of citizen scientists in REMFA we will
be able to fill geographical gaps of information, and gain insights into
wildlife mortality in areas where systematic studies are lacking.
A limitation in out compiled dataset is the assumption of correct
taxonomic identification in systematic studies (and our own correct
identification in non-systematic records). For example, some species
were reported outside their known distribution ranges in Ecuador:Neacomys amoneus, Mesoclemmys heliostemma, Myrmochanes hemileucus,
Pseudocolopteryx acutipennis, Rhogeessa io, Scinax ruber, andXenoxybelis argenteus, and even one species not distributed in
Ecuador was reported (Rhinella arenarum ). These may be
misidentifications (likely for R. arenarum ), but previous
roadkilled specimens have revealed new distribution areas for certain
species (Medrano-Vizcaíno & Brito-Zapata, 2021). Roadkill records can
provide valuable information about the biology and ecology of species
and with correct taxonomic identification contribute to our
understanding of biodiversity.
Road ecology research in Ecuador is gaining interest, but is still
relatively limited. Promoting and guiding additional research and public
engagement is important. Through our citizen science project REMFA we
have given a special relevance to science communication, which has been
vital to reach citizens to join our work, and we are now engaging with
policy makers. The active involvement of government ministries such as
the Ministry of Environment, Water and Ecological Transition, together
with the Ministry of Public Works is necessary for the inclusion of
adequate policies to reduce wildlife mortality across existing roads,
and to plan sustainable roads for the future. We hope that this work can
be an initial step towards these national aims for wildlife
conservation.