Across the U.S. Southeast and mid-Atlantic, cheery daffodils, brilliant forsythias and delicate pink-and-white cherry blossoms are blooming unseasonably early. Some have already peaked, with their vibrant petals turned brown with wilt—and it is only mid-March. Migratory birds such as the Nashville Warbler have touched down several weeks ahead of schedule, and on blades of grass in New York State and other spots, ticks have perched, poised to latch onto their first victims of the season, since February.

These premature signs of spring were spurred by a mild winter across much of the country’s eastern half. Twelve states had their warmest January and February on record, and another 18 had ones in their top 10 warmest, according to the National Oceanic and Atmospheric Administration. Some places, including New York City and Nantucket, saw the earliest signs of spring—such as unfolding leaves and blossoming flowers—on record, according to data from the USA National Phenology Network.

Humans may welcome the chance to put away our coats early. But off-schedule springs can have devastating ecological impacts, from pollinators missing the flowers they usually visit to an increase in conflicts between humans and animals as hibernations are cut short. “A really early spring can lead to all sorts of unexpected problems,” says Morgan Tingley, an ornithologist at the University of California, Los Angeles. The situation will only worsen as climate change makes warmer winters and earlier spring conditions ever more likely. “The issue is when really early springs don’t just become the exception; they become the rule. And that is what we are seeing with climate change in general,” Tingley says. “The extreme has become the typical.  That’s when we start to see stronger, really negative impacts.”

The study of the way species time their behavior with Earth’s cycles is called phenology. For example, birds migrate as the days shorten or lengthen; leaves turn gold or red when temperatures drop. When ecologically intertwined species fall out of alignment with their seasonal cues, it’s called a phenological mismatch.

Flowers that bloom in early balmy weather run the risk of mismatching with their primary pollinators—such as hummingbirds or bees—which can follow non-climate-dependent cues such as day length. That means pollinators will miss out on the nectar they need for energy, and the flowers also won’t be fertilized at their regular rate. Those plants will produce fewer seeds and, in the case of crops, fewer fruits. Botanist Susan Pell, executive director of the U.S. Botanic Garden in Washington, D.C., is particularly worried about fruit tree harvests this year. “We’re seeing pretty much everything blooming much earlier than it normally would,” she says. Fruit trees are also in danger if they bloom early because they could still experience a sudden frost if the weather changes, which can destroy the delicate buds that ultimately yield fruit.

Earlier flowers also mean an earlier release of pollen, which can extend the usual seasonal misery for those with allergies. In Washington, D.C., maple trees let loose their pollen—a major allergen—several weeks ago. Earlier in March Atlanta and Raleigh, N.C., saw a record-breaking onset of high pollen counts.

On the other end of the spectrum, not all flowers will bloom early; some tie their efflorescence to the amount and quality of sunlight they receive. But those that do so can mismatch with pollinators that emerge ahead of schedule as a result of warm weather. If the primary flowers they rely on haven’t bloomed, there won’t be anything for them to eat. “I heard some anecdotal accounts ... of dead bees being witnessed on the ground,” says Theresa Crimmins, director of the USA National Phenology Network. Some biologists speculate that warm temperatures might have lured the bees out of their winter rest and that they then starved without the right flowers being open.

When early springs are coupled with warm winters, it also extends the window for some pests to munch on plants—or on people, in the case of ticks. Without a deep freeze, these arachnids and various insect pests don’t die off en masse, Pell says. This can also spell higher populations in spring and summer.

If insects emerge early because of warming temperatures, their numbers could also peak before the birds that munch on them arrive or before the birds’ chicks hatch. Tingley’s research suggests some birds are advancing their migrations with warming but only at around half of the rate at which plants are now emerging in spring. And other studies have found that insects are mostly keeping pace with plants’ advancement. In Raleigh several bird species showed up early this year—including the Black-and-white Warbler and the Nashville Warbler, says Deja Perkins, an avid birder and urban ecologist at North Carolina State University in Raleigh. “It’s a delight but also a concern,” she says.

Aside from phenological mismatches, early springs open the door to another problem. A recent study found that climate change amplifies human-wildlife conflicts by altering where animals are located and how they behave. One example is bears’ hibernation. Mild winters and early springs lengthen bears’ active season, which draws them into close contact with humans more often as the animals search for food.

Ultimately, scientists don’t yet fully understand the extent to which earlier springs and warmer winters will ripple through ecosystems (and our daily lives). More long-term research is needed to tease apart how species’ relationships with one another will be affected. Citizen science projects that track events in nature can help researchers understand the effects of these seasonal shifts, Perkins says. For example, the USA National Phenology Network’s Nature’s Notebook app, the California Academy of Sciences’ iNaturalist social network and the Cornell Lab of Ornithology’s eBird app all let anyone report the seasonal shifts they notice in their areain leaf buds, insect emergence or bird sightings, for exampleand compare what they see with observations from previous years.

“It brings into focus, for people that don’t necessarily think about climate change on a day-to-day basis, that, indeed, conditions really are changing,” Crimmins says. “We are poised to potentially see some pretty significant impacts.”