Birds are a staple of any UK garden.
In the summer months, an explosion of life can be seen in and around our gardens and countryside, as hungry months eagerly stock up on food and race to breed.
Come winter, however, there is a considerable reduction in the number of birds in our gardens.
But why?
Well, there are various reasons. From natural migrations to spikes in diseases, this article aims to explore why there seems to be fewer birds in our gardens over the winter.
Birds Migrate South For The Winter
The most obvious reason for the apparent lack of birds is simply because they are no longer around.
During the summer months, temperatures and environmental conditions are relatively stable. Oftentimes, there is an abundance of food, which can support healthy populations of birds of all species.
In winter, however, resources are depleted. Temperatures plummet and storms become more prevalent. All of these factors make survival increasingly difficult.
So, how best to avoid poor environmental conditions?
Easy! To leave altogether.
The process whereby an animal travels from one region to another is referred to as migration.
There are a variety of different types of bird migrations. However, the most common forms displayed by UK species are:
- Seasonal Migration – The movement of species between breeding and non-breeding regions.
- Latitudinal Migration – The movement of species from North to South, and vice versa. Many UK garden birds disappear in the winter, as they travel South to warmer climates.
Many bird species that can be found in gardens across the UK in the summer months make arduous journeys in search of warmer climates.
In temperate regions, such as the UK, it is estimated that at least half of our birds are migrants. This is especially the case for insectivorous birds, which migrate to where insects are more abundant.
UK Migratory Bird Species
Some of the most famous migratory species found in our gardens are swallows.
Twice yearly, these small, highly aerial birds embark on an impressive 6,000 mile migration between the UK and South Africa.
During the summer months, swallows gorge themselves on flying insects, such as horseflies and grasshoppers. Come autumn, populations of insect prey dramatically decrease.
To avoid starvation, these little birds, weighing just 20 grams, travel up to 200 miles per day to reach new foraging grounds.
But hey, I think I would battle exhaustion and starvation if it means getting out of a British winter.
A very similar species to swallows, the swifts, also travel thousands of miles every year to escape the peril of British winter’s.
Departing from the UK between June – August, new data has revealed that swifts can travel between their breeding sites in the UK to their new foraging grounds in Africa in just 5 days. They have been known to stop in countries bordering the Atlantic coast of North Africa.
However, these highly agile birds aren’t the only ones to leave our gardens.
Whitethroats, and other warbler species, as well as thrush species, such as wheatears, also take to the sky as winter approaches in the UK, leading to further disappearances in our UK garden birds.
In October, having spent the summer months breeding in the UK, whitethroats leave our shores and make the treacherous journey to Sahel, just south of the Sahara.
This dry area is prone to periods of drought which, if for prolonged durations, can affect the overwinter survival of whitethroats. In the late 1960s, a severe drought in the region led to a 90% population crash in the UK population on whitethroats.
West Africa is a popular winter destination for many UK bird species. Cuckoos, redstarts and turtle doves also leave UK gardens and disappear over the winter period.
Changes To A Garden Setting
Once overlooked for their small size, and seeming inability to house significant environmental resources, gardens have now been proven to be a vital hotspot for many ecological niches.
Not only can they offer foraging opportunities for a variety of bird species, gardens can also provide shelter and nesting spaces – especially with the addition of artificial features such as bird feeders and nest boxes.
However, many bird species are highly neophobic. They do not like change and are wary of novel items.
But, when you’re on the menu for a lot of other species, this is understandable.
Have you changed the layout of your garden? Added any new features? A new washing line perhaps, or even a garden gnome?
Even features that would seemingly increase a bird’s survival, such as new feeders, may be the very reason that birds are no longer visiting.
All it takes is a bit of patience.
It takes just a couple of brave, or hungry, birds to eventually inspect the new settings. Eager eyes watch and wait, ensuring the coast is clear before joining.
Declining Populations
There is a final, more sinister reason as to why you may be seeing fewer birds in gardens over winter: population declines.
There are a range of different factors that influence population declines. Some, such as diseases, can be seasonal. Other factors, such as climate change, are having long-term implications on our garden birds.
Disease Affects Garden Birds
For humans, the common cold becomes progressively more pronounced in the winter. People remain indoors and within close proximity to one another, allowing the disease to spread like wildfire.
Well, something similar occurs in birds.
Avian influenza, or bird flu, is a highly contagious respiratory disease that affects many different bird species.
However, during the winter months, a more serious strain of avian flu, known as highly pathogenic avian flu (HPAF), has been taking a toll on bird species commonly found in gardens.
It is thought that migrating waterfowl species, such as ducks and geese, act as carriers for the disease, spreading it to susceptible species, such as reed buntings.
HPAF spreads from bird to bird via contact with infected salvia, nasal secretions or feces. It can also be transmitted by predation. However, once this aggressive strain of flu makes its way into a population, the damage can be irreversible.
Bacterial bird infections, such as that of Salmonellosis, is another problem for many garden birds over winter, especially seed-eating birds such as sparrows and finches.
With natural food resources depleted, different species of garden birds may congregate in one centralized location, such as a bird feeder, where food resources are still plentiful. With such a high volume of birds in one area, droppings will inevitably accumulate.
Bird feces, infected with the Salmonella bacteria, contaminate food items, which are then ingested by other hungry birds looking for an easy meal. This is referred to as faeco-oral transmission.
The combination of viral and bacterial, as well as parasitic, infections over the wintering period can cause serious population declines to our garden birds.
In the last 11 years, populations of chaffinches have fallen by 30%, whilst populations of greenfinches have decreased by 67%. Both of these declines are attributed to disease outbreaks.
Habitat Loss
When we talk about habitat loss, it is easy to think of the industrial deforestation occurring in our tropical rainforests.
Now, while this is a serious global issue, habitat loss occurs all across the globe. Habitat loss is the destruction of any habitat which supports native species and is more broad than just the loss of trees.
Swifts, swallows and house martins, for example, often nest in old buildings close to a water source.
For successful nests, it’s all about location, location, location. The nest itself has to be easily accessible, and free of obstructions such as branches. Typically, nest sites for these species are under eaves of old houses.
However, many old properties are being redeveloped or torn down altogether to make way for new developments, leaving no suitable nesting sites for these small birds.
Many new homes are seeing the switch from natural to artificial lawns. This blatant destruction of habitat destroys natural foraging grounds, removes nesting material and increases competition for suitable nesting sites.
If you absolutely have to use artificial grass, and I strongly suggest you reconsider, try adding natural borders of native flowers, bird feeders, insect houses and nest boxes, and leaving any larger trees.
Climate Change
Climate change has been negatively affecting wildlife populations throughout the world.
However, some of our resident UK garden birds may have actually benefited from a changing climate. Some species, such as the nuthatch, have colonized new, northern areas which were historically too cold for the small bird. And, as a response, have disappeared from gardens further south.
But, whilst some birds seem to be better off, impacts on other bird species, especially migratory birds, have been far more dire.
Long-distance migrants, such as swallows and whitethroats, do not benefit from the warmer winter temperatures. These species are also affected by weather conditions in their African wintering grounds.
As the climate in these parts of the world increases, we’re experiencing more severe droughts, intense storms and frequent wildfires. All these factors are destroying natural bird habitats at a faster rate than usual.
As a result, UK breeding populations of winter migrants fluctuate in relation to weather conditions in Africa.
Migration Problems
As a response to climate change, investment into the green energy sector has seen an enormous boost.
One of the most endorsed green energy schemes, wind farms, seem like a great idea to provide an alternative to fossil fuels.
And, whilst they are, offshore wind farms are having negative impacts on migratory bird species.
As migratory birds travel across open oceans between Africa and the UK, the risk of collisions with turbine blades is increased, affecting overall populations of birds, further decreasing populations seen in gardens.
Final Thoughts
Bird populations in our gardens fluctuate seasonally.
During the summer months, a bountiful supply of food and stable environmental conditions sees a large bird diversity visit our gardens.
However, when conditions become less favorable, almost half of our bird species migrate southwards, vacating our gardens for the winter period.
Unfortunately, climate change is affecting migrating birds; both in the UK and wintering countries, such as Africa. Climate mitigating strategies, such as wind turbines, are also negatively affecting migrating birds through collisions.
Want to make a difference? Try a bit of citizen science this winter period and record the bird species you see in your garden. Submit findings to the RSPB to help scientists track bird numbers.
