The phenomenon of bird migration has fascinated people from the earliest times. Recently, evidence has grown that the migratory behaviour of many bird species is changing in response to human-induced environmental change. Non-migratory individuals have been reported either in increasing frequency in partially migratory populations or in previously wholly migratory populations. Whilst the mechanisms that drive changes in migratory behaviour and how contrasting migratory strategies affect the survival rates and demographic parameters of residents and migrants within a population are poorly known, this has implications for our ability to conserve species and use them as monitors of the global environment.

The iconic White Stork is a very adaptable species, opportunistic species. Since the mid-1980s, increasing numbers of White Stork have chosen to stay in Iberia all year rather than migrate to Africa in winter. Some of the birds that winter in Portugal are from breeding population in Central and Eastern Europe. Resident birds rely almost exclusively on the guaranteed, abundant food supply from landfill sites during the winter. They have benefited from milder European winter temperatures.

In Portugal several landfill sites will close at the end of 2014 and during 2014, this presents a unique opportunity to study the consequences of a dramatic reduction in winter food availability for resident individuals of a partially migratory population.