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Early springs in UK leaving birds hungry

According to new research, the warmer springs which are arriving earlier than before in the UK is causing birds to go hungry. As caterpillar numbers spike too early due to the slightly higher heat that comes weeks before it usually should means that by the time many bird eggs have hatched, there is no longer enough food to go round. This is just one part of a wider trend that has seen the life cycles of many animals and plants disrupted by the changing climate.

Caterpillar numbers spiking early

These disruptions are not just within the natural world, it also has effected how humans and animals co-exist. For example, in Finland, the Northern lapwing and Eurasian curlew have typically made nests among the crops after the farmers have sown their seeds so that the eggs hatch whilst the farmers are not in operation. This rhythm has now been thrown off by the warmer temperatures, meaning that concealed nests are now being destroyed by tractors due farmers moving their schedules three weeks back. These out of sync movements which we are seeing between animals and their surroundings are due to global warming, Dr Karl Evans at the University of Sheffield puts it simply that: ‘Previous work has shown a mismatch does lead to population declines’, whilst Dr Malcolm Burgess, who carried out the new research expands by saying, ‘Forests have a short peak in caterpillar abundance, and some forest birds time their breeding so this coincides with the time when their chicks are hungry.’

Dr Burgess then explains that this means there is now an added pressure on birds to breed early because of the shifting environmental conditions: ‘With spring coming earlier due to climate change, leaves and caterpillars emerge earlier and birds need to breed earlier to avoid being mismatched. We found that the earlier the spring, the less able birds are to do this.’

Pressure on birds to match the changes

The study in question focused on blue tits, great tits and pied flycatchers. Using data collected largely by a national network of citizen scientists to explore the spring emergence of oak tree leaves and the caterpillars that feed on them, and the timing of nesting by the three bird species, they were able to show that the biggest mismatch was among the pied flycatchers. Birds such as these who migrate (with pied flycatchers migrating from sub-Saharan Africa in the beginning of the spring) are far less well equipped to shift their own understanding of when breeding season should commence than birds who are native all year round and so able to pick up slightly better on the changes as they happen.

All of these disruptions to the life cycles, migratory habits and breeding patterns of birds which have been etched into their life cycles in an evolutionary manner of course combining with other factors leading to an overall decrease in bird populations in the UK including the overuse of pesticides which has lead to severely depleted numbers of insects.

Uncertainties about evolutionary capacity

Although Dr Evans notes that birds are gradually changing their breeding patterns to adapt to the changing environment and specifically to the earlier springs, he suggests that, at the moment, this change is not happening quickly enough for this not to continue to have a hugely negative impact on the populations of birds in the UK. Although, this is just a theory at this stage, Dr Evans makes it clear that: ‘People are starting to look at whether there’s capacity for evolutionary change to improve their ability to match, but the evidence is very mixed at the moment.’


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