Identification of Green Iguana (Iguana iguana) Hotspots in Urban Kaohsiung Using Citizen-Reported Geographic Information Dataset from the Kaohsiung City 1999 Call Center
This study utilizes citizen-reported data from the Kaohsiung City 1999 call center to identify spatial hotspots and migration patterns of invasive green iguanas, revealing their concentration in the city's mid-to-southern regions, expansion via specific bridges and waterways, and potential spread toward Tainan City.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
In the bustling cities of southern Taiwan, a quiet ecological shift is underway. Green iguanas, large reptiles native to Central and South America, have established themselves as a permanent part of the local landscape. Originally brought to the region as pets, many were later released or escaped into the wild, where the warm climate allowed them to thrive without natural predators. These animals are considered an invasive species, meaning they are not native to the area and can disrupt local ecosystems by competing with native wildlife and altering habitats. For city planners and conservationists, the challenge is not just knowing that these lizards are present, but understanding exactly where they are clustering and how they are moving through the urban environment. Without precise maps of their distribution, efforts to manage their populations can be scattered and inefficient.
To solve this puzzle, researchers turned to an unexpected source of data: the city's own residents. In Kaohsiung, a major port city in southern Taiwan, citizens can report issues ranging from broken streetlights to environmental concerns to a municipal hotline known as the 1999 call center. In 2025, the city received thousands of reports from people spotting green iguanas in their neighborhoods. A team of scientists from National Kaohsiung Normal University and Kaohsiung Medical University decided to treat these reports as a valuable map. By converting the street addresses provided by callers into precise geographic coordinates, they created a detailed picture of where the iguanas were being seen. They then used a statistical method to identify "hotspots"—areas where sightings were significantly more frequent than in surrounding neighborhoods, indicating a true concentration of the animals rather than just random chance.
The analysis revealed a clear pattern of movement. The highest concentrations of green iguanas were found in the central and southern parts of Kaohsiung, with a secondary cluster forming in the northwest. The data strongly suggests that the invasion is moving from the neighboring Pingtung County into Kaohsiung City. Two major bridges connecting the two regions appeared to serve as primary entry points. The researchers found that the density of sightings was highest within a specific radius of these bridges, dropping off as one moved further away. This pattern indicates that the animals are crossing the river via these bridges and then spreading outward into the city. The study identified a boundary roughly 9,750 meters from the bridge endpoints where the density of sightings changes character. Inside this zone, the iguanas are densely packed and actively expanding their range. Beyond this distance, sightings become less frequent and are mostly found along waterways like rivers, canals, and ditches, which are known to be preferred habitats for the species.
Interestingly, the study also uncovered a new frontier of expansion in the northwestern districts of the city. Here, hotspots were detected near major roads and bridges that lead toward Tainan City, a neighboring municipality to the north. This suggests that the green iguanas are not just settling in Kaohsiung but are preparing to move further north, potentially following the same route they took from Pingtung County. The researchers noted that while the city government has been removing thousands of iguanas, these efforts often focus on areas that are easy to access or where young, smaller lizards are found. The data from the citizen reports offers a more comprehensive view, highlighting specific villages and neighborhoods where the adult population is most dense. By focusing removal efforts on these identified hotspots, particularly targeting the larger, breeding adults, authorities could potentially slow the spread more effectively than current methods allow.
The study concludes that the 1999 call center provides a powerful, low-cost tool for monitoring invasive species in urban areas. Unlike specialized apps that require users to have smartphones and specific knowledge, a phone call is accessible to everyone, including elderly residents who might otherwise be excluded from scientific data collection. This approach captures a broad demographic of observers, creating a continuous stream of information that helps officials see the big picture of an invasion as it happens. The findings confirm that the green iguana population in southern Taiwan is not static; it is a dynamic force moving through the city's infrastructure, using roads and bridges as corridors. By mapping these movements with the help of everyday citizens, scientists and city managers can now target their resources more precisely, aiming to protect the local ecosystem before the spread becomes even harder to control.
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