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A migratory question.


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#1 Game Warden

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Posted 03 April 2016 - 11:08 AM

Do migratory birds ever vary their routes in the event of some ecological/environmental change? Or learn to avoid areas where there is human interference?

 

Instances I'm thinking of are obviously the impact of global warming, loss of habitat due to land use change, and hunting such as happens in Malta during the spring

 

Are there any scientific studies or papers worth reading?

 

 


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#2 Game Warden

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Posted 03 April 2016 - 11:12 AM

As I am writing this, I came across this article in the Washington Post. There’s a reason some birds don’t seem to fly south for winter anymore, scientists say

 

The reason for my question is that we would hear cuckoos at specific times up until last year when a large swathe of forest was cut down close to the HQ. 


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#3 Peter Connan

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Posted 03 April 2016 - 11:39 AM

While not scientific at all, i have noticed that some birds move through my area some years but are not seen in other years.
As to the reasons, i can't even speculate meaningfully.
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#4 Tom Kellie

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Posted 03 April 2016 - 12:31 PM

As I am writing this, I came across this article in the Washington Post. There’s a reason some birds don’t seem to fly south for winter anymore, scientists say

 

The reason for my question is that we would hear cuckoos at specific times up until last year when a large swathe of forest was cut down close to the HQ. 

 

Platalea minor at Hong Kong Wetland Park.jpg

 

Platalea minor at the Hong Kong Wetland Park

 

Photographed at the Hong Kong Wetland Park on 17 January, 2014 at 1:43 pm with an EOS 1D X camera and an EF 400mm f/5.6L super-telephoto lens

 

ISO 100, 1/1000 sec., f/5.6, handheld Manual mode exposure

 

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Very sorry to hear of the loss of cuckoo habitat.

 

As with mammals, so with birds.

 

A one-size-fits-all generalization may not fit the wide variety of cases.

 

Species and their sub-species considerably vary in their tolerance of change, i.e. certain species are remarkably adaptable while others are relatively inflexible.

 

An example of an avian species which has adapted to enormous pressure from human interference is Platalea minor, Black-faced Spoonbill.

 

An endangered species with around 2,000 individuals, they survive in areas where there's very limited efforts to preserve the conditions that they need for breeding.

 

Yet they're hanging on in part due to their adjustments in migration and wintering patterns to avoid as much as possible the bleak, hostile territory through which they travel.

 

They're a modest success story with a grim long-term prognosis. Other Safaritalk members may have more pertinent examples.

 

Tom K.


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#5 offshorebirder

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Posted 07 April 2016 - 07:12 PM

Do migratory birds ever vary their routes in the event of some ecological/environmental change?

 

 

The answer is yes, they do so regularly.   For example, here in the eastern USA, in some years southbound passerines (particularly Warblers, Flycatchers, Vireos, Tangers, Orioles and other small songbirds) in the fall travel south in vast numbers along the immediate coastline.  Other years, they do so mostly down the Appalachian mountains or their foothills, well to the west of the coast and coastal birders have a very poor fall migration experience.   This is believed to be in response to prevailing weather and wind patterns. 

 

Another example:  "fallout" in migratory stopover habitat.  Background:  most migrating songbirds do not like to cross large bodies of water in daylight or inclement weather.  Daylight due to falcons, hawks, etc targeting them in the open with no shelter for escape.  Inclement weather because of the downdrafts over bodies of water and because rain and wind can cause them to lose momentum/flight efficiency and they may have to put down in a hurry - which is impossible over a large body of water.  So patches of good habitat (even small ones) directly bordering the large bodies of water are known as "migrant traps" - because they are an irresistible lure for migrants who have to put down in a hurry when approaching a large body of water and dawn breaks, there is bad weather, etc.   When such habitat is destroyed, or created, the migratory birds either cease using it or begin using it, depending.  At a large harbor or bay, vast lake, etc. - when such habitat appears or disappears, it can cause migrants to shift their routes and migratory stopover points anywhere from a few miles to a few dozen miles depending.  

 

In terms of the Malta example, the sad fact is that many birds have no choice but to stop there.  It's a survival tactic for tired and hungry birds crossing large expanses of the Mediterranean sea.      Birds crossing large deserts also have no choice but to stop at oasis and any riparian corridors they may be able to find when they "run out of fuel". 

 

And so if climate change caused a river to dry up and riparian habitat to disappear, birds crossing a given desert or dry scrubland would have to alter their route to find another stopover oasis, mountaintop, or riparian corridor.

 

With @Game Warden's specific example of the forest being cut and no longer hearing Cuckoos - that sounds like a migratory stopover location was destroyed/degraded and migratory Cuckoos had to stop over (or "fall out') elsewhere.  

 

Loss of migratory stopover habitat is one of the biggest looming threats for migratory birds.  To conserve migratory birds we obviously need to protect their breeding grounds and "wintering" (nonbreeding) grounds, but also need to preserve a chain of suitable migratory stopover habitat at regular intervals along their migratory routes.

 

* In terms of @Peter Connan's observation that he sees some kinds of birds migrating through his area in some years and not others - same over here.  I have always thought it is a combination of two things:   1.  The above example of variation in response to prevailing weather patterns   2.  Here in years without much rain, we get fewer (or no) "fallout" events from migratory flocks encountering rain and deciding to set down in decent stopover habitat.   When there is nothing but "blue skies and clear sailing"  the thinking among birders here is that the birds tend to sail past without being forced to stop as often so birders don't see them as they fly over invisibly at great height.  Many migratory songbird species (and some shorebird species) can and do fly continuously for multiple days without stopping or resting. 

 

 

-- In terms of @Game Warden's question about whether migratory birds "learn to avoid areas where there is human interference" - I have not heard of such but that's not to say it doesn't take place.  But if the human interference consists of destroying or degrading migratory stopover habitat, then yes the birds would be forced to look for suitable habitat elsewhere.  


Edited by offshorebirder, 07 April 2016 - 07:18 PM.

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#6 Towlersonsafari

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Posted 07 April 2016 - 07:47 PM

Hello @Game Warden look on the BTO website (British Trust for Ornithology) as they have been tracking cuckoos for a number of years and you can see the routes individual birds take.Another example is Ospreys who often return to their breeding sites on the same day each year, given reasonable weather.Try the Rutland osprey site. I think Roy Dennis has also been tracking migrating birds of prey.Some Ospreys now over winter in Spain instead of West Africa. Increasingly Blackcaps over winter making use of bird food put out in gardens and of course milder winters in the uk
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#7 Atravelynn

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Posted 07 April 2016 - 09:37 PM

Great question.  Insightful responses.

 

One other activity that halts migration is people feeding birds throughout winter months.  Not saying this is bad.  I feed the birds.  One species that has altered its behavior to take advantage of bird feeders is the Cardinal in the US, which did not used to remain north throughout the winter.


Edited by Atravelynn, 07 April 2016 - 09:38 PM.

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#8 offshorebirder

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Posted 07 April 2016 - 10:44 PM

Due to winter feeding I think, we also get a lot of overwintering Hummingbirds in the southeastern USA in recent years - including western species like Rufous and Black-chinned Hummingbirds.
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