Penguins inspire a special fascination, even among people who might not normally care about birds. Perhaps it’s their shuffling waddle, their bright, contrasting colors or their stoic, heroic huddles in the face of frigid Antarctic winds. Despite their charm, “if you annoy them, they’ll stab you in the face with their bill,” says Ron Naveen, the founder of nonprofit conservation group Oceanites. A new report issued Tuesday by the group says that although Antarctica has an abundance of these charismatic birds, some penguin populations have suffered huge losses over the past few decades.

About six million breeding pairs of penguins currently live in Antarctica, according to the report. That number is expected to change as the organization finalizes ongoing surveys. But Naveen says one trend is clear: some species of penguin have experienced dramatic shifts in population sizes as parts of the continent have warmed. The report combines all available data on the five species of penguins that breed on the continent, including satellite imagery, ground counts and other estimates, providing a comprehensive overview of the state of penguins in the Antarctic for the first time in more than two decades.

Oceanites’s report reveals several important large-scale population trends, says Naveen, who has traveled to Antarctica almost every year over the past three decades to study penguins. The findings show that two species—Adélie, the most ubiquitous on the continent, with a white ring around their eyes and short beaks, and chinstraps, named for a distinctive line of dark feathers under their faces—are declining on the Antarctic Peninsula, which juts some 800 miles north from the continent toward South America. In this area populations of the two species have dropped by as much as 50 percent since the 1980s. At the same time gentoo penguins—which live in the same region and have orange bills and white dashes over their eyes—have grown in population by about 40 percent during that period. “That leads us to start thinking about climate change and why one species is adapting better than another,” Naveen says.

Naveen thinks the rapid warming of the peninsula through the second half of the 20th century may have caused these shifts (although the region has cooled slightly since the 1990s). No one has proven why these penguin populations are dwindling, but Naveen speculates melting glaciers and ice sheets around the peninsula could change the balance of krill and fish penguins eat. If gentoos can adapt their diet more readily than Adélies can, then that may be why they are thriving in that region. Michelle LaRue, a research ecologist at the University of Minnesota, confirms the importance of sea ice for organisms like krill. "Krill need sea ice to survive," she explains. LaRue says there is a strong correlation between reduced sea ice and decreased krill populations.

Naveen notes that in East Antarctica, on the opposite side of the continent from the peninsula, Adélie numbers have in fact grown. In the east, Naveen says, “it’s colder—there has not been a similar warming trend.” Emperor and macaroni penguins are the other Antarctic species, but not enough long-term data exists yet to determine how their populations have changed across the continent.

All the species play a critical role in the Antarctic ecosystem, according to LaRue, who uses satellite imagery to study Antarctica’s penguin populations. Not only do they eat krill and many species of fish, they are also important prey for leopard seals. Naveen hopes this report will be used by organizations involved in Antarctic management and conservation. The Commission for the Conservation of Antarctic Marine Living Resources, an international group comprising 24 countries and the European Union, is in charge of regulating fishing for krill and toothfish (also marketed as Chilean sea bass) in Antarctic waters. Naveen says the commission could use this report to make decisions about regulating fishing and to help justify its rules.

The report draws heavily on a new database Oceanites helped launch last year called the “Mapping Application for Penguin Populations and Projected Dynamics,” or MAPPPD. This open-access project lets scientists—and anyone interested in penguins—visualize and work with data on the locations and numbers of penguin colonies in Antarctica. LaRue, who was not involved with the new report, says that in the past, information on different species or on penguins in different regions were only available separately. But “the Southern Ocean and Antarctica is not piecemeal—it’s all connected,” she says. “This puts it all in one spot.” Heather Lynch, a researcher at Stony Brook University who helps run MAPPPD and is currently working on an updated survey of chinstrap penguin populations, agrees. “Having a single open-access data set that everyone in the community can use is a big deal scientifically,” she explains. “For once, we can start working on models and analyses on an agreed[-on] data set, rather than everyone using their own.”

Louise Emmerson, a research scientist with Australia’s Department of Environment and Energy Antarctic Division, raises some issues with the database though, including errors in data on the site—both in terms of actual numbers used and because satellite imagery can sometimes generate false positives, incorrectly identifying marks such as sediment runoff as guano stains from penguin colonies. “This is concerning and has the potential for detracting from conservation efforts,” she says. Emmerson hopes the database will go through a peer review process in the near future; Naveen says that process is underway.

Ultimately, Oceanites plans to produce reports like this one annually. As more data comes into the MAPPPD database, estimates will improve and long-term trends will become clearer. Climate change will likely continue to influence population trends, Naveen speculates. But Emmerson also notes changing penguin populations cannot be attributed solely to climate change—food webs, the fishing industry and disturbance from tourism can also affect penguin populations. “One of the difficulties we have as scientists is trying to understand what is driving these [population] differences,” she says. “This is an incredibly complex thing to decipher.”