Have you ever noticed there is some difference between city trees and forest trees? A new study finds city trees grow faster but die younger than trees in rural forestry.

As we all know, the earth would be freezing or burning hot without carbon dioxide. However, carbon dioxide is a greenhouse gas, meaning it traps energy from the sun as heat. That makes temperatures near the ground rise. Human activities, especially the widespread burning of fossil fuels, have been sending extra greenhouse gases in to the air. This has led to a rise in average temperatures across the globe.

Studies had shown forests readily absorb carbon dioxide, but there hadn’t been much data on whether city trees grow, die and absorb carbon dioxide at the same rate as forest trees do. So some researchers decided to find out.

To figure out how quicky trees were growing, researchers tracked their diameters (the width of their trunks) between 2005 and 2014. A tree’s diameter increases as it grows, just as a person’s waist size increases as they gain weight. The research has shown about half the weight of a tree is carbon, while most of the rest is water. Over the nine years’ tracking, the researchers found city trees absorbed four times as much carbon dioxide from the air as forest trees. However, they were twice as likely to die. So over the lifetime of each type of tree, forest trees actually absorbed more carbon dioxide.

City trees grew faster because they have less competition for light from their neighbors. In a forest, trees tend to grow close together, shading their neighbors. Street trees also benefit from higher levels of nitrogen (氮) in rainwater. Nitrogen helps plants grow. Waste gases from gas-burning cars also contain nitrogen, thus enriching city air with nitrogen. Later, rainwater may wash much of it to the ground. Some street trees may also have better access to water than trees in the country because the underground water pipes can leak.

Population data for European mountain birds have been for the first time combined in a recent study, with worrying results: the abundance of mountain-specialist birds has declined by as much as 10% in the 2000s.

Ecological communities in mountain areas include species not found in any other habitats. These species are also very susceptible to climate change, as global warming is reducing their liveable habitats. In principle, species may relocate further up the mountains, but closer to the top their habitat inevitably shrinks.

According to the new article,the abundance of European mountain birds has in fact declined in line with climate change projections.

The recently released study examined the population trends of 44 bird species in the 2000s in the mountain and fell regions of Fennoscandia, Great Britain, the Alps and the Iberian Peninsula. A decline was seen in 14 of the observed species, while eight of them saw significant increase.

“On average, population decline among the species studied was 7% over the 13-year research period, making the situation of mountain birds distinctly worse compared to, for example, European forest birds, whose numbers did not change during the same period,” explains Aleksi Lehikoinen, an Academy of Finland research fellow at the Finnish Museum of Natural History Luomus (part of the University of Helsinki), who headed the study.

The situation is direst for species that only inhabit mountain regions and are unable to live in other European environments. For these species, known as mountain specialists, the numbers dwindled by as much as 10% during the monitoring period.

The ability to use tools is rare in the animal world. Recently, cockatoos(凤头鹦鹉) have been proven capable of more than just using tools.

According to a paper published in Current Biology in February, 2023, scientists designed various tasks for a group of cockatoos. The first task was getting a nut out of a puzzle box, requiring two tools: first a short, sharp tool used to cut the membrane(薄膜), then a long stick to get the nut out of a hole. Five out of 10 cockatoos were able to reach the nut. In the following tasks, the cockatoos were observed picking up tools before doing the task, showing their ability to plan ahead. Researchers also noticed that each cockatoo had a different way of carrying and using the tools.

Using a set of tools means that the animal can “solve problems through flexibly applying some insight of a given situation,” Mark Briffa at the University of Plymouth, UK, told CNN.

The great intelligence of cockatoos makes them popular pets—they can mimic(模仿) sounds and dance to music. However, these smart birds may suffer from mental health issues as well. Common signs of stress and anxiety include biting and feather picking, according to the PetMD website. Biting is often regarded as a form of attack, but sometimes cockatoos bite others due to stress and fear. Feather picking can be a more serious sign that the cockatoo is unhappy. In extreme conditions, a cockatoo may pluck(拔) out all of its feathers.

Some other pets show similar troubling behaviors too. For example, according to Discover magazine, pet dogs may chew their nails or lick their bodies so much that they form ulcers(溃疡). Pets desire attention, joy and excitement. As scientists learn more about animal intelligence, we should keep in mind that they may suffer from psychological illnesses just like we do.