Birds under threat from climate change: study

By Mark Waghorn via SWNS

Birds will raise fewer chicks in the coming decades because of climate change, warns new research.

An earlier spring makes it harder for them to know when it is time to breed, the new report reveals.

Our feathered friends are struggling to keep pace. The phenomenon has been dubbed "ecological mismatch."

Study first author Dr. Casey Youngflesh, of Michigan State University, said: "By the end of the 21st Century, Spring is likely to arrive about 25 days earlier, with birds breeding only about 6.75 days earlier.

"Our results suggest that breeding productivity may decrease about 12% for the average songbird species."

Birds' readiness to reproduce is likely to become worse as the world warms - which would be catastrophic for many species.

Breeding seasons begin whenever the first green plants and flowers appear - which is happening earlier and earlier as the climate warms.

In the UK plants are already flowering almost a month earlier on average.

Just as autumn leaf fall is being delayed by warmer weather, flowers are appearing earlier on trees and shrubs.

There are knock-on effects for birds, insects and whole ecosystems.

Global warming is causing spring to arrive early and autumn to come late in many places. Not all plants and animals are adapting at the same rate.

If species get out of sync with each other it could have disastrous consequences.

Pollen, nectar, seeds and fruits of plants are important food resources for insects, birds and other wildlife.

And if flowers appear too early they can be hit by frost, damaging the harvest of fruit trees.

Conservation strategies should address birds' responses to climate-driven shifts, says the US team.

Determining if the earlier springs will pose problems for migratory birds has been a major goal of biologists for decades.

Senior author Professor Morgan Tingley, of California University, Los Angeles, said: "For nearly 30 years, scientists have hypothesized that animals could become mismatched from plants as springs begin earlier.

“While there have been a few very good case studies of this phenomenon, it has remained a major mystery whether advancing springs will pose a general problem for the majority of species.”

When it comes to raising their young, timing matters for birds. If they breed too early or too late, harsh weather could harm their eggs or newborns.

The same applies to food. If birds are looking for grubs before or after their natural availability, they might not have the resources to keep their young alive.

Tingley said: "Critically, we found evidence for impacts on bird reproduction of both the absolute and the relative timing of birds."

The researchers analyzed large-scale bird banding data from the Institute for Bird Populations in which small colored rings are fitted to individuals' legs.

It enabled them to calculate the timing of breeding and the number of young produced for 41 migratory and resident species at 179 sites near forests across the US between 2001 and 2018.

Satellite imaging determined when vegetation emerged around each location. The study found each species had an optimal time to breed.

The number of young produced decreased when spring arrived very early, or when breeding occurred early or late relative to when plants emerged.

Most were adversely affected by variations in the start of spring. Several species countered the trend, demonstrating improved breeding productivity when spring began earlier.

They included the northern cardinal, Bewick’s wren and wrentit. They are non-migratory species that can respond more quickly to the emergence of spring plants that signal the start of the breeding season.

By breeding earlier and without the time constraints imposed by migration, non-migratory species may also be able to reproduce more than once per season.

But those species were the exceptions to the rule. Even most non-migratory species couldn’t keep up with earlier spring arrivals. Overall, for every four days earlier that leaves appeared on trees, species bred only about a day earlier.

For migratory species breeding is likely to get shorter as spring-like conditions begin earlier.

Birds need time to establish territories and prepare physiologically for egg-laying and rearing their young.

The change could cause even greater disturbances to reproduction.

Tingley added: "North America has lost nearly a third of its bird populations since the 1970s."

"While our study demonstrates the worst impacts of timing mismatch likely won't occur for several decades yet, we need to focus now on concrete strategies to boost bird populations before climate change takes its toll."

The study was published in the journal Proceedings of the National Academy of Sciences.