Marine bird poop is helping cactus forests grow on desert islands. By studying samples from Isla San Pedro Mártir and other islands, researchers found that seabird guano provides a lot of nitrogen to the soil, which boosts cactus growth. The nitrogen levels in the cacti on bird islands are much higher than those on mainland or non-bird islands. This shows that seabird poop is a key factor in making cactus forests thrive in these harsh environments.