The Trust has been investigating the wildlife benefits of growing hemp compared with oilseed rape and field beans.
The study revealed that all three crops were used by birds as habitats for gathering food during the nesting season, but hemp was also used as a roosting site by swallows before their southward migration at the end of the summer.
Flocks of more than a thousand swallows were seen using the hemp fields on the GWCT's research farm at Loddington, Leicestershire.
Another migratory bird that was associated with hemp was whitethroat - a warbler that breeds on farmland throughout the UK.
Researchers found that some other bird species made more use of oilseed rape and bean crops.
Dr Chris Stoate, head of research at the GWCT research farm, said: "We know that hemp has low requirement for inputs such as fertilisers and pesticides, but we needed to investigate whether there are any effects on wildlife of a crop that is relatively new to modern farming systems.
"Our research found that numbers of insects, including those used as food by birds, were broadly similar in the three different crop types. Weed cover and weed species did not differ greatly between the crops, which was surprising as hemp grows vigorously, shading out competing weeds so that herbicides are not needed."
But growing hemp has other environmental advantages as well, said Dr Stoate.
"The wider environmental benefits for growing this crop are considerable. The findings confirm that hemp benefits some wildlife species, as well as requiring minimum pesticide and fertiliser use during production," he said.
The research was carried out at the GWCT's Allerton Project research farm and was funded by Hemp Technology, a processor of hemp for the construction industry