Scent (2 Viewers)

[George Hogg]

As a naturalist and working dog handler I have developed a fair understanding of mammal scenses,particularly their ability to hunt using scent.

This leads to me often feeling uneasy about bird nest surveying as I beleive any human scent trail will be followed after dark by predatory mammals,straight to any nest inspected earlier.

I feel if birders had a better understanding of the importance of scent in mammal behaviour we would be much more reluctant to approach nests however carefully.

What do others think?

 

[citrinella]

Hard to dismiss George. May I post this to the Nest Record Scheme discussion forum ?

Mike.

 

[fugl]

As a naturalist and working dog handler I have developed a fair understanding of mammal scenses,particularly their ability to hunt using scent.

This leads to me often feeling uneasy about bird nest surveying as I beleive any human scent trail will be followed after dark by predatory mammals,straight to any nest inspected earlier.

I feel if birders had a better understanding of the importance of scent in mammal behaviour we would be much more reluctant to approach nests however carefully.

What do others think?

I've heard this said before & I'm not sure what I think about it. Have there been any scientific studies on the subject, do you know?

 

[Adam W]

I can understand the therory behind your concern but i would have thought if it were a problem it would have been noticed before now but who knows maybe not and maybe it needs looking into.

 

[dantheman]

Would predatory mammals be likely to investigate the scent trail left by a human, or rather shun it completely??

If the latter, then the occasional visit to a nest site should possibly be of use to the nesting birds!!

Interesting ...

 

[ChrisKten]

Totally unscientific, but don't Animal Trappers make a point of removing Human scent, as Mammals avoid the area if they detect the scent?

And if so, then I agree with Dan's last sentence.

 

[citrinella]

Interesting ideas on human scent deterring mammalian ground predators. If that argument were sound, you might expect disturbance of vegetation round nest sites by humans to have some deterrent effect. It doesn't, avoiding disturbance of vegetation near a nest, even where it doesn't cause visual exposure to a nest, is a key practice nest recorders must adopt.

Also against the scent deterrent ... human beings are pretty bloody obvious. In general the predators George is talking about are far more aware of our presence than we are of theirs. They are also far more patient and have far greater fieldcraft skills. They might detect a human scent, but they won't follow it blindly. They would be sure to move around to cover all the blind spots in their perception of danger, especially if the trail was moving downwind.

George has a good point about wild animals perceptual acuity often being far better than hours. It is so good that it is obviously better to humans ! that sounds like a truism, but it isn't. It is really difficult to comprehend something that is completely beyond one's own abilities. Cases that have been recognised - mammals that can detect their own species in heat at many miles distant; vultures that can fly so high surveying the ground for prey that they are completely invisible to humans even using good binoculars; mammals that can find other members of the same species by sound over many miles (e.g. elephants) or, in the ocean, perhaps hundreds of miles.

We know these things, but it is still an ability that is hard to imagine.

On the trap point, removing human scent. Yes, we do (I have to trap rats see http://www.birdforum.net/showthread.php?t=187697). Any animal observing a human scent will be on alert. That doesn't mean instant flight, they are instinctively aware of the dangers of giving their position away unnecessarily. It means assessing every aspect of the environment for dangers before proceeding. So an unnatural looking object (trap) would then be something to avoid.

Mike.

 

[LabradorDuck]

Even if human scent doesn't keep predators out of an area, I have a hard time believing it would attract them. Visual exposure of a nest is a different issue, as that would attract predators no matter its cause. For predators to follow human trails looking for bird nests would require them to develop an association between the two, which would be unlikely unless the only humans that came through the area were successful nest-searchers, and this continued over a long period.

That's not to say that humans can't cause problems. I believe I have heard of some shorebird projects where devices designed to exclude certain predators began to attract others. However, a lone human wandering through the woods is unlikely to be perceived as a source of bird eggs.

 

[George Hogg]

Even if human scent doesn't keep predators out of an area, I have a hard time believing it would attract them. Visual exposure of a nest is a different issue, as that would attract predators no matter its cause. For predators to follow human trails looking for bird nests would require them to develop an association between the two, which would be unlikely unless the only humans that came through the area were successful nest-searchers, and this continued over a long period.

That's not to say that humans can't cause problems. I believe I have heard of some shorebird projects where devices designed to exclude certain predators began to attract others. However, a lone human wandering through the woods is unlikely to be perceived as a source of bird eggs.

Hi George again,Here is my opinion for what it is worth(I am a wildlife manager of over 30 years experience and author of Practical Pest Control)
I don't beleive predators follow human scent on the off chance of eggs,they do it because they are opportunists and one predator will follow another's ( including human) scent in hopes of food scraps.
Also they know exactly the age of the scent they are following ,so can tell you were there by day and are now long gone.
To perdators a scent trail is as obvious as a wide path of dayglo paint.
I just think we should be aware of how obvious a trail we leave when we visit a nest.
As regards removing human scent,a predator or even an experienced dog would just think oh there has been a human here three hours ago trying to mask it's scent,must find out why!

 

[George Hogg]

I can understand the therory behind your concern but i would have thought if it were a problem it would have been noticed before now but who knows maybe not and maybe it needs looking into.

If someone visits a nest then later finds it raided by a mammalian predator ,would they realise it was possibly because of human scent?
As birders tend not to be widely experienced with mammals,I doubt it.

 

[George Hogg]

Hard to dismiss George. May I post this to the Nest Record Scheme discussion forum ?

Mike.

Hi Mike feel free to use my questions and air my concerns,it can do no harm and could do a lot of good....George

 

[MJB]

I don't beleive predators follow human scent on the off chance of eggs,they do it because they are opportunists and one predator will follow another's ( including human) scent in hopes of food scraps.
Also they know exactly the age of the scent they are following ,so can tell you were there by day and are now long gone.
To predators a scent trail is as obvious as a wide path of dayglo paint.
I just think we should be aware of how obvious a trail we leave when we visit a nest.

George,
The following is circumstantial, but a couple of Montagu Harrier nests in North Norfolk were predated by foxes that may well have followed the trail through the crop left by the farmers, who, although very supportive of protecting the birds, were perhaps over-keen to ensure the nests were still occupied. No proof, of course, but the red fox is not only opportunistic, but also remarkably persistent in exploring anthing new in its hunting range.
MJB

 

[George Hogg]

George,
The following is circumstantial, but a couple of Montagu Harrier nests in North Norfolk were predated by foxes that may well have followed the trail through the crop left by the farmers, who, although very supportive of protecting the birds, were perhaps over-keen to ensure the nests were still occupied. No proof, of course, but the red fox is not only opportunistic, but also remarkably persistent in exploring anthing new in its hunting range.
MJB

Hi MJB,in U.K.foxes associate humans with litter,incl.food scraps and regularly check out human scent trails...g

 

[fugl]

So then, in view of the lack of responses to my question way back in post #2, I take it there haven’t been any scientific studies on the subject? Is that right?

 

[mauricek]

nd As a doghandler gEORGE WILL KNOW THAT IF HE TELLS ADOG TO STAY SOMEWHERE ATHEN LEAVES IT FOR AWHILE AS HE GOES OFF AND PRETENDS TO STOP AND LOOK AROUND ONTHE GRASS OR VEGETATIONhis gog becomes intrigued and the moment he he allows it free it will dash off to see what he's been doing.
The same could happen if any scavenger picks up on a persons behaviour.
We/I still have agret deal to lrarnItis a fscinating subject.
Sorry about the caps but Im 86 an almot blind.

mauricek ex A.S.P.A.D CDex UDex

 

[ovenbird43]

So then, in view of the lack of responses to my question way back in post #2, I take it there haven’t been any scientific studies on the subject? Is that right?

It seems I've come across some in the literature, but I don't remember any specifics. Journal of Wildlife Management seems a likely place to look, and I believe the most recent issues are publicly available online. Also try checking the Searchable Ornithological Research Archive (SORA- http://elibrary.unm.edu/sora/) although I suspect one would be more likely to find such research in more recent issues of those journals.

 

[mr.sim]

As regards removing human scent,a predator or even an experienced dog would just think oh there has been a human here three hours ago trying to mask it's scent,must find out why!

Do you think some of the smaller predators would really be this "intelligent"? Maybe something more like "Hmmm, faint human scent...ooh a worm! :eat:"

Seriously though, would smaller mammals actually take that rough thought path?

 

[George Hogg]

Do you think some of the smaller predators would really be this "intelligent"? Maybe something more like "Hmmm, faint human scent...ooh a worm! :eat:"

Seriously though, would smaller mammals actually take that rough thought path?

Hi Mr Sim,what i am trying to get across is that mammmals see and read scent as clearly as you are reading this.and understand from it many aspects of the time,behaviour,demeanour and intentions of the creature or person who left that scent.just as you work out the plot of a book as you read it.

Nor are they at all fooled or confused by multi scents i.e that of a human and a manufactured scent erasing product.I beleive they would instantly separate the two scents.
Also when coming on multi aged scents they can tell instantly the order in which those scents were laid .
Their evolutionary survival has depended on this level of sensitivity.
To put it simply they see through their noses.
I watch my dogs do it every day.

 

[mr.sim]

Surely then if predators have this level of scent ability then there's not a lot we can do about it? Except maybe reduce visits to nests...

 

[Dave_Leech]

Nest monitoring and predation risk

Hi all,

As Head of the BTO's Nest Record Scheme I have read the postings on this thread with interest - many thanks to Mike for bringing it to my attention.

It will be of no surprise that this is a topic of interest to all researchers working on breeding birds and, in response to Fugl's question, yes, there have been a substantial number of scientific studies investigating the effects of nest monitoring on the eventual outcome. A key review paper is:

Götmark, F. (1992) The effects of investigator disturbance on nesting birds. Current Ornithology 9,63-104

which examined the published results from studies across a wide range of species and countries and concluded that the majority of these concerning solitary nesting species find no detrimental effect, although it does highlight the need for care when entering colonies of colonial nesting species.

A study by two of my predecessors, Henry Mayer-Gross and Humphrey Crick:

Mayer-Gross, H., Crick, H.Q.P. & Greenwood, J.J.D. (1997) The effect of observers visiting the nests of passerines: an experimental study. Bird Study 44, 53-65

explored the question using Nest Record Scheme data and again found no evidence for detrimental effects of nest visitation. Advances in remote monitoring technology are making it much easier to carry out this sort of research and two more papers relevant to the current thread include Keedwell & Sanders 2002 (www.jstor.org/pss/1370718) and MacIvor et al. 1990 (www.jstor.org/pss/3809656), the latter demonstrating that foxes do not use observer trails to cue into Piping Plover nests.

This does not of course mean that anyone monitoring nests should not take great care - the welfare of the birds is paramount, and the protocols laid out on the Nest Record Scheme website (www.bto.org/volunteer-surveys/nrs/taking-part/nrs-code-conduct) should always be adhered to.

I hope you find this response useful - the contact details for the Nest Record Scheme are on the web-pages, so please feel free to contact us if you would like any further information.

Many thanks, Dave Leech