A yellowhammer is one of the populations in decline, according to the study. Photo: Andy Hay/RSPB
The number of birds in Wales continues to decline with two species, curlews and golden plovers, seeing an 80% drop in population, RSPB Cymru has said.
The charity is also concerned for birds which breed on four estuaries, including the Severn and the Dee.
But its annual survey found some good news, with the near-threatened Dartford warbler having 72 pairs in Wales.
And the seabirds kittiwakes, fulmars and guillemots are doing better in Wales than in other parts of the UK.
A study suggests populations of some breeding birds on farmed habitats, such as curlews, starlings and yellowhammers, are continuing to decline unabated.
It found curlews had declined by 81% throughout their range in Wales, down to some 1,099 breeding pairs, between 1993 and 2006 and golden plovers by 88% between 1982 and 2007.
The survey put the Welsh breeding population of golden plover at 36 pairs, compared to an estimated high of 214 pairs in the mid 1970s, although different survey methods mean the figures might not be directly comparable.
However, house sparrows have increased in Wales against a backdrop of significant declines in England, one of eight species that have increased since 1994, including carrion crow, swallow, house martin and stonechat.
Some seabirds are doing better in Wales but starlings and curlews are continuing to decline
The survey, which covered the Severn and Dee estuaries, Burry Inlet in Carmarthen Bay, and Traeth Lafan, Conwy Bay, found the fulmar and kittiwake populations have remained stable since the mid 1990s, while guillemots seemed to be faring better than in the UK as a whole.
Katie-Jo Luxton, Head of Conservation Policy at RSPB Cymru, said: "Some of Wales' important bird species are now so scarce they cannot be monitored by annual schemes.
"This dramatically shows that we don't have much time left to act if we are to save these special birds in Wales."
Dr Siân Whitehead, Senior Ornithologist for the Countryside Council for Wales, said: "Climate change is already impacting our bird life in Wales - causing changes in habitats and loss of food supplies for some species, while others, such as the Dartford warbler, are already benefiting."
Richard Hearn, Head of Species Monitoring for the Wildfowl & Wetlands Trust said: "We are concerned over the declining status of some of our water birds on key estuaries in Wales, such as the Severn and Dee."
And Derek Moore, chairman of the Welsh Ornithological Society, added: "It should be of great concern to everybody that once common breeding species such as curlew and lapwing are almost as rare as the enigmatic red kite."
The fifth annual snapshot of Wales' bird population was published by RSPB Cymru in conjunction with the British Trust for Ornithology (BTO), the Countryside Council for Wales (CCW), the Welsh Ornithological Society (WOS) and the Wildfowl and Wetlands Trust (WWT).