The garden of 1979 was filled with glossy gangs of starlings, the atonal chirp of sparrows and the tap-tap of song thrushes breaking open snail shells.

In 2019, you’re more likely to hear the screech of a ring-necked parakeet, the “coo” of a collared dove or the “woo” of a woodpigeon.

The Big Garden Birdwatch is marking its 40th year this weekend, with half a million people expected to spend an hour counting the birds in their garden or local green space in what is the world’s biggest wildlife citizen science project.

The RSPB survey reveals sharp vicissitudes of fortune for our garden visitors over the years. Starlings have fallen by 80%, song thrushes by 75% and house sparrows by 57%. Even ubiquitous garden heroes the robin (-31%) and blackbird (-41%) have become more scarce.

A woodpigeon (Columba livia) feeding on berries in a UK garden in Autumn (October). Photograph: Alamy Stock Photo

But gardens have filled with different sights and songs, with woodpigeons bustling in to view, rising by 950%. Collared doves are up 307% and magpies – viewed with suspicion by many small-bird lovers – have risen by 173%.

Some small songbirds are thriving, however: coal tit numbers are up by 263%, wrens by 88% and there are regular top ten appearances by long-tailed tits and goldfinches, the latter thought to be lured by nyjer seeds put in bird feeders.

The 130 million bird sighting records have charted the rise of ring-necked parakeets across London and the south-east, and the resurgence of the reintroduced red kite – people are allowed to record this big bird of prey if it is seen flying over their garden rather than in it.

The Big Garden Birdwatch has also alerted conservationists to the decline in song thrushes, which was a top ten regular in the early days of the survey. By 2009 its numbers were less than half those recorded in 1979. After disappearing from much of London by the turn of the century, the house sparrow has rallied in the last decade, its numbers increasing again by 17%. Farming schemes to provide winter seed for birds have helped house sparrows in rural areas.

Mike Clarke, RSPB chief executive, said: “Everyone has a role to play in saving nature and protecting our wildlife. Big Garden Birdwatch participants have made a significant contribution to monitoring garden bird numbers over the past four decades.

“It’s an enjoyable, easy, inclusive activity that anyone can do and a great opportunity to connect with nature.”

Starlings (Sturnus vulgaris) are among several species to have suffered “alarming” declines in the last 40 years, the Big Garden Birdwatch findings shows. Photograph: Andy Hay/RSPB Images

While many of the population trends are caused by forces beyond gardeners’ control, including climate change and an intensification of farming, people can make their backyards and green spaces more bird-friendly. The RSPB recommends keeping gardens chemical-free, allowing bushes and thick hedges to grow, and providing bird food, water and north or east-facing nest boxes.

Participants are asked to spend an hour on Saturday, Sunday or Monday recording their local birds and sending the results to the RSPB. This year people are also being asked to look out for frogs, toads, grey and red squirrels, foxes and badgers, as well as muntjac and roe deer.