Gloria Dickie

LONDON, (Reuters) – The early bird gets even earlier.

With climate change spurring earlier springs across much of North America, many birds are laying their eggs earlier in the year, according to a new study – adding to mounting evidence that global warming is turning wildlife habits upside down.

In a paper published in The Journal of Animal Ecology on Friday, scientists report that approximately a third of 72 birds in Chicago laid eggs around 25 days sooner than they did one hundred years ago.

The mourning doves, American kestrels and Cooper’s Hawk are among those affected.

The scientists so far haven’t found any clear traits shared by these species, such as size or migratory status, that might explain why they’re changing their schedules.

John Bates (curator of Field Museum’s bird division in Chicago) said that “the vast majority of birds examined eat insects.”

Bates explained that it’s becoming more important to think about how seasonal and climate disruptions affect animal and plant life cycles.

A few degrees below the average temperature can make a huge difference in when insects emerge, what time trees grow leaves and when the flowers bloom.

According to Science, scientists believe that these changes are among the reasons why bird populations have declined steeply since 1970s. The United States and Canada lost roughly one third of their birds in this period. This is a total loss of approximately 3 billion birds.

Bates, along with his collaborators, studied nearly 1,500 eggshell records kept at Chicago’s Field Museum. These records date back to 1872-1920 when eggs were a common pastime. These Victorian era ova enthusiasts left detailed, handwritten labels listing information such as the bird’s species and collection date.

These records were then compared with over 3,000 contemporary records. The data also included information about the carbon dioxide levels for nesting dates and time.

Similar results were obtained from similar studies in Britain in recent years. These also showed that eggs are laid earlier than previously thought.