Warm spring upsets links between birds, insects and trees

FEW WILL complain as we bask in this week’s unseasonal sunshine – but the phenomenon has consequences beyond delivering the first sunburn of the season.

Spring is arriving earlier each year and it is turning the tight relationships between birds, trees and insects on their head.

The amount of change is significant, said Dr Alison Donnelly of Trinity College Dublin’s Centre for the Environment. Beech trees growing on Valentia Island, Co Kerry, now begin breaking leaf a full month earlier than they did 40 years ago, she said.

Birds that migrate from the sub-Sahara now tend to arrive about seven days earlier than in the past, including the common cuckoo, bard swallow and sand martin. But this is late compared to their main food source, the insects, whose numbers rocket weeks earlier as they feed on sap delivered by the opening leaves.

Scientists and interested members of the public have catalogued the phenology or timing of these life-cycle events in plants and animals over decades, Dr Donnelly said. These sensitive life-cycles pick up the impact of climate change.

The phenology of flora and fauna in autumn, when birds migrate and leaves wither, is driven by diminishing sunlight and cooler air, but temperature is the key factor in spring, she said. This made the science an ideal way to gauge the impact of climate change on the living environment. “Phenology is the only real climate-change indicator that looks at how the change affects plant and animal life,” said Dr Donnelly, who heads Trinity’s phenology group. “It is also a really good way to convince policy makers about the reality of climate change.”

Dr Donnelly has written the 10th Scientific Statement from the Climate Change Sciences Committee of the Royal Irish Academy. The report shows people do not need to guess how climate change will affect Ireland – it is already evident. “We are seeing a very clear signal and seeing the effects in our back gardens,” she said. “People are saying they have to cut the grass all year long.”

It spells trouble for confused birds and bugs, the horticultural industry and people who suffer from hay fever. Birds arriving late for the spring insect feast will have less food and fewer fledglings, while earlier insect populations will rise without birds to cull them. The biodiversity of a region can shift with alterations to the predator/prey mix.

Late frosts are another threat, she said. These can kill young birds while insects can also be wiped out, producing a gap in the food supply. Fruit that sets early is also in jeopardy.