The research into European Turtle Dove declines shows that the brood numbers in Northern Europe in the 60s were 3-4 in a season and then from the 90s just one. This alone would largely account for the rapid decline in the species.
Also Turtle Doves did sustain hunting at a likely higher or at least similar level than more recently. The changes in agricultural wiping out food supplies are the critical aspect here but hunting a rapidly declining species will only further exacerbate the problem.
Spain hosts 1,370,000–2,285,000 pairs (c.41% of European breeding population) so clearly an important source breeding population (also the area of La Brenne in France is a great place for the species with a very high breeding / occupied territory density). These two areas are interesting as gut analysis of birds shot in Southern Spain showed a high concentration of wild plant seeds (and obviously there is an array of natural areas and important plants like fumitory grow abundantly in these areas and also in La Brenne) compared to those retrieved from more intensively farmed areas. Other parts of Spain and Europe are continually intensifying agriculture mostly to feed livestock causing this lack of food resources.
The Turtle Dove is mostly an obligate granivore (mostly consuming seeds) and requires summer seed source from once commonly occurring countryside plants. Modern herbicides and agricultural practices have wiped these species out and one of the casualties is the European Turtle Dove – along with a whole host of farmland birds and other wildlife.
Additionally the agricultural change on wintering grounds for export agriculture to Northern Europe is an issue equally wiping out naturally occurring seed sources. We gave a talk about the issues in Africa at the African Bird Club AGM in London – https://www.youtube.com/watch?v=iVrcwAjzC7s
This lack of food in the countryside has placed the adults under increasing food stress making them more susceptible to disease. This is likely spread from non native captive bred introduced Pheasants – in fact trichomoniasis detected in swab analysis of TDs detected strains of the disease found commonly found in Pheasants! So a reduction in numbers being released is urgently needed (the levels in the UK are completely unsustainable).
There is some talk of reintroducing birds from captive stock – which to me is ludicrous because the species still exists, the problems are still in effect and the birds would not have migratory instinct therefore robbing Africa of returning European Turtle Doves! Plus any introduction should follow IUCN guidelines (regardless if the species requires licensing for reintroduction) – one of which clearly states that the problems and causes for decline must be significantly addressed before reintroduction.
Hunting is often the most emotive issue that receives a lot of attention but the fork remains one of the most powerful tools for conservation and what we eat determines how the vast majority of land is managed.
As ever the issues are multivariate the solutions however are achievable. One step closer….we hope!