Fera said the tags were not ideal for use on active young lambs
Radio tags used to track young lambs during a study into whether they were preyed on by sea eagles were "not ideal", researchers have reported.
More than 167 tags were fitted to lambs in Wester Ross, but about 60% fell off.
The Food and Environment Research Agency (Fera) said it had been a "labour intensive" process catching lambs to reattach the devices.
The project concluded that the impact of the raptors on flocks studied was "minimal".
The fortunes of selected lambs in three flocks in Gairloch were monitored to help determine whether large numbers of livestock fall prey to the raptors.
Crofters in the area and on Skye had claimed the birds fed on their stock.
Scottish Natural Heritage (SNH), which commissioned the research, said the study suggested less than 2% of lambs' deaths were directly linked to the birds.
Seabirds were found to be the raptors' main source of food.
Radio tags were used to help monitor individual lambs.
In the newly-published report, Fera said the radio tags were effective in providing information where lambs were but there were problems with the type and size used.
The report said: "Large square radio tags with sharp corners are not ideal when species to be tagged are active young animals within rough habitats and wet climate.
"Furthermore the overall shape, dimensions and weight were far from ideal in terms of tag retention when attached directly to the study animal."
The researchers went onto highlight the role of crofters and shepherds in rounding up lambs to reattach lost tags.
The report said: "Not only were the actual methods of attachment labour intensive but gathering in more animals to reattach dislodged tags involved not only excessive amount of the study team's time but also further time from the crofting community.
"Without the unprecedented help from key crofters, the radio tagging and tracking would not have been possible."
The agency disputed claims that the tags had put off eagles from going for live lambs.
Researchers said the device was no more visually intrusive than the coloured letters and numbers sprayed on the animals' backs as part of normal flock management.