New in Wildlife Science: Bird–Building Strikes & Marlin Stripes

The updated numbers on bird–building collisions are worse than we thought; plus, marlins’ color changes and tall grass benefits for butterflies

By Mark Wexler
Wildlife Science
Mar 26, 2025

Undercounting Bird–Building Strikes

To estimate the toll taken by bird–building strikes, scientists have relied on counting dead birds at crash sites (above). But according to two recent studies, totals derived from such counts are too low. “The truth is there are many birds that collide and don’t immediately die,” says Ar Kornreich, a Fordham University biologist who led a project examining records of 3,100 building strikes by 152 bird species between 2016 and 2021. Writing in Plos One, she and her colleagues report that more than half of rescued crash victims ultimately died—and suggest the number of U.S. bird-collision deaths far exceeds 1 billion annually. In another five-year study ending in 2022, Muhlenberg College ornithologists analyzed data from field experiments and from 10 U.S.-based wildlife rehab facilities. They found that half of all window strikes leave no evidence of a collision and as many as 70 percent of rescued birds succumb to their injuries. Writing in The Wilson Journal of Ornithology, they estimate at least 3.5 billion birds may die each year from window collisions in this country—a 350 percent increase over earlier estimates. Birds fly into buildings, lead author Daniel Klem says, if windows reflect trees or the sky. “Ninety-nine percent of all the windows in the world are reflective,” he adds.

To learn more about bird-window strikes—and how to make your windows more bird-friendly—see: abcbirds.org/blog/truth-about-birds-and-glass-collisions/.

An image of a comma butterfly.

Boost Backyard Butterflies

Analyzing five years of butterfly sightings in more than 600 gardens across Great Britain, scientists have found that letting a portion of lawn go wild can increase the number of butterflies (including commas, above) in residential yards. The study provides compelling evidence that “undertaking simple wildlife-friendly garden practices can be beneficial for attracting butterflies, particularly in heavily modified areas,” says co-author Richard Fox, head of science at the British nonprofit Butterfly Conservation. In their analysis, the researchers explored whether specific practices, such as providing nectar plants and tall grasses, attracted butterflies. They report in Science of the Total Environment that urban properties with patches of unmowed grass, for example, showed an average of 18 percent higher butterfly abundance than properties with no long grass. Several butterfly species use tall grasses as larval host plants. Some caterpillars, meanwhile, continue to feed on long grass throughout winter while the eggs and pupae of other butterflies shelter in the plants. “The best approach for homeowners,” says Fox, “is to always have some long grass available.”

An image of a striped marlin chasing a ball of mackerel fish.

Color-Coordinated Attacks

Among the swiftest animals on Earth, striped marlin form groups to hunt, taking turns attacking prey with their pointed bills. Using high-resolution drones, biologists from Germany’s Humboldt University captured rare footage of the predators pursuing sardines off Baja California Sur in Mexico. In the footage, they observed that the stripes on each individual marlin (above) became noticeably brighter, turning iridescent blue, as the predator charged into the sardines. When the marlin retreated, its stripes dimmed back to dull blue-gray. “Although it is known that marlin can change color, this is the first time it’s been linked to hunting or any social behavior,” says lead author Alicia Burns. Published in Current Biology, the study notes that striped marlin have light-reflecting crystals in cells on their bodies that they expose and “turn on,” as the scientists put it, when they’re about to attack prey. Through such displays, a marlin may be signaling its intentions to group mates, alerting them to stay back.

An image of a bench on a patio garden with blooming perennials.

Microscope

Power of Nature

People whose surroundings feature abundant trees and wildlife (including in gardens, pictured) enjoy better mental health than those living in environments with less natural diversity, King’s College London researchers conclude in Scientific Reports.