Why Do Blackbirds Abandon Their Nests?

Blackbirds have fascinated me for years and, other than Sparrows they appear to be one of the most common birds I see. I was lucky enough to have a Blackbird build a nest in my back garden earlier this year. But, for some reason, she decided to leave once the nest was complete. Why was this? Why do Blackbirds abandon their nests?

There are two main reasons why a Blackbird (or any bird) will abandon its nest. Firstly and maybe the most common is because they feel threatened – there is a danger of harm to them or their young. Secondly, it is because they have finished raising their young, fledglings have taken flight and there is no further use for the nest.

It is important to remember that birds build and use a nest for just one reason – hatching and raising their young. Birds do not generally use a nest as a year round living space. This is why you only see them building at a certain time of year.

For one, the babies don’t stay small for long and a family of full sized birds will easily outgrow a nest. It seems as though the Blackbird building a nest in my back garden felt threatened by something. So much so, she decided to nest elsewhere.

Why Do Birds Abandon Their Nests With Eggs?

So here is the cruel twist of nature – even if a Blackbird has laid eggs in her nest, evolution has programmed her and many other animals to instinctively choose their own survival over protecting their unborn young. Let me explain…

Just like humans, most other living thing relies on four things to exist – food, water, reproduction and survival. Without any of these we die. There is a choice for Mrs Blackbird to make when there is a threat of attack – fight to protect her unborn babies, or live another day to produce more offspring.

Like many other species of bird, the female Blackbird will be forced to abandon their nest, even their eggs, in favour of being able to survive to reproduce again. If she is fit and healthy she can continue to raise many young over her lifetime. There is little point in spending valuable time and energy protecting unhatched young in a nest which is under threat.

What Are The Threats To A Blackbird?

There are many things perceived as dangerous by a nesting bird. They are mainly predators (including humans) and pests, like hornets and wasps. If a Blackbird begins nest building in the spring before a back garden becomes overrun with noisy children and pets, all might seem good. As soon as the weather warms up and the garden get daily use, that changes and the location is no longer viable for her.

My Blackbird in particular chose to build her nest against a fence behind some thick honeysuckle. She had clearly chosen this location for the protection given by the climbing plant. It was March too, before we really used our garden very much since the new year.

A noisy neighbour going in and out of his shed at all times of day (right behind the fence panel the nest was on!) probably didn’t help. This was followed by a busy back garden with humans close by, then a neighbouring cat skulking around the place. It is no wonder the Blackbird fled, luckily before she lay eggs.

More Than One Nest

It has also been known for a Blackbird to make more than one nest in different locations. The purpose of this is likely to test each nest to decide which is going to be the safest and less likely to come under threat. It would make sense, then, that a nest or two will be abandoned for no other reason than this.

Do Blackbirds Reuse Their Nests?

Blackbirds are known to re-use their own nests a number of times during their current breeding season. They are even known to re-use a nest during the following year’s breeding season. Often they will take up residence in a previously used nest by another bird. However, a Blackbird will not use it’s nest if it has been compromised or unsuccessful in raising a brood. If you want more detail, keep reading…

The overriding factor which influences nest re-use by Blackbirds is how successful breeding is in that nest. The key to this appears to be site selection and protection – protection from predators as well as the elements. It might sound obvious but nests that are built in higher locations and well protected from damage are shown to be more successful and therefore favoured for re-use.

A detailed study by Dariusz Wysocki, entitled: ‘Nest Re-Use by Blackbirds – The Way for Safe Breeding?‘, recorded 35 instances of nest re-use by Blackbirds. In over 90% of those cases the Blackbirds used their own previously successful nests. In a little over 5% they used a nest previously built by another Blackbird. In just a few cases the breeding couple took over the nest of another species of bird.

The study also documents how on only two occasions did a pair of Blackbirds re-use an unsuccessful nest. Around 40% of pairs re-used their nest on successive breeding attempts within the same season. You can find the full paper by clicking here.

All information available supports the theory that ‘predator avoidance’ is the most common factor influencing a Blackbird to re-use it’s nest. Nests that are higher up, better protected and out of site are likely to be more successful and re-used. Wysocki concludes that:

“… nest re-use is a predator avoidance strategy. In most Blackbird populations that have been studied, the concealment of the nest is the most important determinant of successful breeding.”

Do Blackbirds Nest In The Same Place Every Year?

Quite often a female Blackbird will choose the same location in successive years. This is not thought to be that frequent, however, it is known. Going back to the study by Wysocki, one female was seen to return to the same nest, in a well protected tree hollow for four years in a row. Having attempted to raise a brood in two other locations, both were unsuccessful and she returned to the old nest again and again.

How Many Times A Year Do Blackbirds Nest?

It is normal for Blackbirds to successfully raise up to three broods in one breeding season. Each brood can be between three to five eggs, incubated by the female Blackbird. She is brown in colour and blends in with her surroundings better than the male.

As detailed above, they may build a new nest for each brood or they might re-use their existing nest. Nest building usually begins in the spring, around March time and continues throughout the spring and summer. Weather can play a part in when birds begin nesting. Bad weather can delay things and warmer weather, or warmer locations can sometimes prompt breeding in the winter.

Each brood is incubated for up to two weeks before hatching. Each hatchling is cared for and fed for another couple of weeks before they are strong enough to leave the nest. Each brood can take a month or so from start to finish. After each brood has grown and left the nest, the breeding begins again.

How To Tell If A Mother Bird Has Abandoned Her Nest

Have you ever had that moment where you see a birds nest that shows signs of life but no adult bird? Maybe you are wondering whether you can safely remove a nest as you maintain your hedgerows or shrubs.

If you intend to move or remove a nest you should observe it for a while. When I say a while, I mean at least a day or two. Often birds will not begin incubating their eggs until the last has been laid. This is so all the eggs hatch at the same time, or thereabouts. So, if there are only one or two eggs in a nest it is entirely possible the mother bird is off feeding or looking for more nesting material.

The danger is that, if you start visiting the nest yourself you may alarm the mother bird and result in the eggs being abandoned. Or, there is a chance a local cat is watching and wondering what you are going back and forth to look at. You can guess what happens next!

What To Do If You Find A Birds Nest

My best advice is to keep the nest under observation for a few days, as much as is possible. If there is still no activity around the nest, maybe try to get close enough to have a look inside. If there are eggs, be cautious as to your next actions. If the nest is empty and the bird has not returned in days, it is probably not a suitable nesting site. It still could be re-used by another bird but it was probably abandoned for good reason and you could remove it.

It is illegal in many countries to interfere with birds’ nests, birds eggs and young birds. You should not touch them if you can help it. However, you can always get in touch with your local wildlife agency for some advice on what to do. While the information on this website is from reputable sources and my own experience, I do not hold any professional qualification or authority to tell you what to do. If in doubt, seek professional advice.