When they have reached their destination, birds that fly long distances suffer from hormonal and behavioral changes , but these anomalies are usually adaptive to the biology of the species and do not pose serious problems. In reality, the most striking disorders manifest themselves before and during the journey. This is when the birds show greater agitation, with strong symptoms of anxiety .
But the most damaging thing for these travelers is the lag weather : due to climate change, the birds do not find the expected conditions at their destination. The species of an ecosystem have different rates of adaptation to warming, and become out of sync with each other with the consequent ecological disaster. For example, when the birds arrive, the caterpillars they feed on have already undergone metamorphosis, leaving them with nothing to put into their mouths.
