Does habitat fragmentation negatively affect all birds? NO! But, it does to many and influences the ecological balance. Here is the full story of how birds are doing in a fragmented world.
Firstly, I need to mention that this is a somewhat technical topic to discuss. But I hope you will enjoy reading it since you will get a lot of new information on the topic. Additionally, towards the end of the article, I have provided some conservation tips for those who want to support bird conservation.
Let’s dive into the details.
What is habitat fragmentation?
Habitat fragmentation is a man-made process where existing large-scale habitat patchers convert into small-scale (with small areas often less than 10 hectares) habitat patches.
Along with habitat fragmentation, habitat loss also simultaneously occurs where a completely alien or artificial matrix is established between the created habitat patches.
As a result of habitat fragmentation and habitat loss, habitat degradation and habitat disturbance also occur which threaten not only bird life but also most other wildlife as well.
Even though habitat fragmentation happens almost in all habitat types such as coral reefs, mangroves, deserts, and even in polar ice caps due to global warming, here we only focus on terrestrial habitat (mainly forests) fragmentation which affects birds directly.
There are many published scientific papers and review articles explaining the massive consequences of forest fragmentation on biodiversity throughout the world.
Human-mediated agricultural expansion is identified as the main cause and most highlighted threat to remaining forests. And especially, in the tropics the existing rainforest areas such as great Amazonian forests, Congo rainforests, and rainforest in the Malay Archipelago experiencing massive pressure due to fragmentation.
You can get a comprehensive idea of forest loss and the drivers of this forest loss which currently has an indirect but strong link with our food from the following documentary.
Yes, it’s difficult to digest that meat or livestock farming or animal agriculture industry is the leading threat to rainforests.
So, some would say going vegetarian is the best way to stop forest fragmentation. Actually, it has some weight on it if we think in the line that, globally, if a massive number of people decide to become vegetarians, the meat industry will collapse and no longer forests will be cleared for livestock farming.
But, in the current circumstances, it is highly unlikely to happen.
Let’s first look at how fragmentation affects birds.
Effects of habitat fragmentation
Loss of critical habitats for many bird species
The very first consequence of fragmentation is habitat loss. Most forest birds highly rely on available habitats to fulfill their daily needs such as to find food, seek protection from predators and find shelter or night roost.
Even a single well-branched bush in a forest acts as superb refugia for forest bird species to hide when threatened by a predator.
Further, the amount of habitat has a direct link with available food sources in a forest habitat. So, the reduction of habitats directly decreases the available food for birds. As a result of habitat loss, birds in fragmented habitats may have weak health and body conditions.
Unhealthy birds with weak traits
If a bird species lives long enough in a fragment, that bird most probably undergoes malnutrition due to a lack of optimum food sources in the fragments. When fragmentation occurs, habitat degradation is also inevitable, thus resulting in poor habitat conditions.
Therefore the individual birds living in a particular fragment need to put more energy to find the daily food requirement or they need to explore the non-forested outside matrix for food.
Both these reasons lead a bird to become a weaker individual and decrease its survival rate. So, even though it may succeed in breeding within the fragments, there is a possibility to pass the weak traits to the next generation.
This results in young birds becoming more vulnerable than the parent birds within a fragment.
Increased predation pressure not only natural but also domestic predators
Even in a larger forest track, it is natural to have predators which control the bird populations. But with the fragmentation and habitat degradation, the visibility within a forest fragment increases, and safe havens (where birds can take cover from predators) get reduced over time.
So the chance to get caught by a predator increases for a bird that lives in a fragment compared with the large track of forest.
Furthermore, the introduction of different matrices, such as agricultural fields and village setups or built-up areas, leads to the roaming of domestic cats and dogs into the fragments thus the remaining forest birds get an intensified predation risk.
Increased nest predation and brood parasitism
Generalist bird species such as Greater Coucal, Crows, and Ravens act as nest predators where destroying nests and eating bird chicks.
With the fragmentation, these birds can easily search for nesting sites as the vegetation gets less dense. This indeed increases nest predation.
Most of the Cuckoo species are known as brood parasites who lay their eggs in other birds’ nests (mostly in Babblers, Iora, Warblers nests). With fragmentation, they also get higher opportunities to find nests and lay their eggs within forest birds’ nests.
Once the Cuckoo eggs hatchers (usually they hatch faster than the host eggs), the newborn cuckoo chicks definitely remove the host eggs from the nest thus no chance for survival for the host bird’s chick.
It has been shown in many scientific studies that fragmentation brood parasitism also increases and ultimately affects the forest bird community in the long term.
Impediment to movements thus affects the gene flow
The ability to perform the movement without any barrier is crucial to long-term survival. Because it facilitates the gene flow of a population to mix with the metapopulations (metapopulation is a spatially separated population of birds with some interactions to a certain level).
Therefore permeability or penetrability of a bird species to a certain matrix is a detrimental factor to the gene flow.
There is enough evidence that some forest specialist birds can not cross even a 10 m gap between forested habitats thus telling us about how non-forested habitats can put impediments to bird movements.
Understory small to medium-sized insectivorous bird species is known to greatly affect my habitat openings.
In other words, if the bird lacks the familiarity to move through a particular land-use type, it simply avoids it at any cost thus affecting the survival of the population through genetic drift.
Local extinction due to long-term isolation
All the above-mentioned factors collectively influence the reduction of the population size of forest birds, especially, habitat specialist bird species to go locally extinct. Thus, affecting the global population in the long run.
Increased population of generalist bird species and interfere the ecological balance
Contradictory results will go for habitat generalists because almost all the habitat generalist bird species can tolerate habitat changes or multi-level land-use types and survive without any issues.
So due to fragmentation, habitat generalists get more advantages due to the introduction of new land-use types such as open grounds, pasture lands, and agricultural fields where they usually thrive.
As a result of that, the proportion of habitat specialists to generalists will change over time and the natural community composition will be affected by it.
So, in a landscape with fragmentation going on you may be able to see an increase in species richness. And this increasing trend may feel superficially good because you get more and more species. But the increase is just due to the invasion of habitat generalists.
What kind of birds are specifically affected by fragmentation
Some would think that birds can tolerate the effects of habitat fragmentation since they can fly. But this is not true for many forest-dwelling birds.
There are two categories of birds in the world, habitat specialists and habitat generalists. This categorization solely depends on the degree of tolerance level of the bird to cope with different habitat types.
For example, a crow can survive in a forested habitat to a highly urbanized and polluted town. But a small understory living bush babbler cannot tolerate even a small canopy opening in the forest.
So, if a bird can tolerate more than one habitat type, we can say that bird is a generalist. But if a bird species is only capable of living in a single habitat type, we put them into a habitat specialist group.
Therefore, habitat specialist birds are undoubtedly affected by habitat fragmentation but generalist birds may benefit from fragmentation.
According to the published papers it has found that large-bodied frugivorous birds such as Hornbills and Forest-dwelling Green Pigeons and insectivorous birds severely affected by fragmentation. And this effect has increased massively in the tropics.
Following lists some of the habitat specialist bird species that are scientifically well-studied in the world.
List of the habitat specialist bird species
|American pygmy Kingfisher
|Amazonian barred Woodcreeper
|Black-throated Blue Warbler
|Western Slaty Antshrike
What kinds of birds get advantages over habitat fragmentation?
Generalists, Nest predators, Brood parasites, Nest hijackers.
As I stated earlier in this post, generalist birds can occupy a wide range of habitat types including highly urban landscapes to forested edges.
Due to their high tolerance range for human activities, they can live among people and also adapt to polluted environments as well.
Because of that they are high in numbers compared with other birds such as Common Mynahs. Nest predators such as Coucals get more advantage over forest fragmentation because they get more opportunities to find nests easily.
Cuckoos are the most famous group of birds as brood parasites. They also get easy opportunities to find nests among smaller fragments where they need to put low energy to search.
Nest hijackers are basically tree cavity nesters such as Common Myna, Rose-ringed Parakeet, and Brown Headed Barbet which are highly opportunistic for tree halls. Specifically, they hijack tree cavities built by other forest birds such as forest-dwelling woodpeckers.
So those forest dwelling cavity nesters face nest site loss due to these invaders and resulting disturbed breeding cycles.
How to mitigate forest fragmentation: Conservation actions
Bird populations are declining rapidly throughout the globe due to many reasons including climate change. And habitat fragmentation is among the leading threats to cause local extinctions of bird life.
Fragmentation also directly influences important ecosystem services such as seed dispersal, pollination, and control of insect herbivory.
Therefore immediate action is needed to mitigate the fragmentation and we need to restore the possible land patchers back with vanished forested habitats.
Then the previously kept bird communities slowly recover and return to the normal natural equilibrium.
So, the need of maintaining minimum fragment size to protect threatened birds from fragmentation, create movement corridors as wide as possible, encourage reforestation programs, and donate for such projects will help to solve the problem.
What we can do about fragmentation as birders
As individuals and as birders, we can contribute to dampening forest fragmentation and mitigating its effects on birds.
Here are some suggestions for you to consider.
- Encourage forest restoration activities and conservation projects and be a fund donor to such projects.
- Try to choose plant-based food over mean whenever possible to influence animal farming which is considered as the leading threat to forests.
- Be an influencer on conservation. Build awareness in your close circles on the effects of forest fragmentation on birds and actions that we can take as individuals.
You may also like: