COMMON CAUSE

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“When you have eliminated the impossible, whatever remains, however improbable, must be the truth”
        Arthur Conan Doyle The Sign Of The Four (1890)

Strange things have been occurring at several of the monitored osprey sites, this season. Unaccountable, worrying things that seem - on the face of it - to be so far removed from the usual that they defy explanation.

17.7.2016 Fledgling Z0 “Ceri"

falls from a perch at MWT Cors
Dyfi and sustains serious injuries
(Infra-red illumination)
[Montgomeryshire WT]

Fledgling birds have been falling from their perches. Youngsters have appeared to have difficulty in walking, holding their legs or talons at strange angles. Some have flown and failed to return; others have gone off their food, seemingly ill, only to recover later. One chick (at MWT Cors Dyfi) has been so badly hurt that she went into circulatory shock and died. And on social media and the forums, everyone has been asking:-

What the hell is going on? 

These are wild creatures and every moment of their lives is at hazard. Bad things can and do happen to individuals, whether they are under observation or not. It's Nature. Flying is an instinctive ability, but the judgement of speed, distance and timing are not: these are acquired skills and they have to be learned and practised. Young inexperienced birds sometimes have accidents, and the outcome depends very much on chance and circumstances. Usually, they get away with it unharmed – but not always. 

We on the other hand are not wild birds. We are human beings and one of our less-rational habits is to search for patterns in isolated events, where often none exist. Psychologists even have a term for it: “apophenia”. Scientists are trained to recognise this trait in their own day-to day work, and to eliminate it in favour of objectivity and rigour.

There's an app for that...

Statistical mathematics include a set of tools that can tell us whether the frequency of an event (or series of events) is higher, lower, or the same as might be expected to occur by chance. Numbers were crunched and the answer came back: it was higher. Not by much, but detectable.

30.7.2016 Osprey W7 sustains

apparent grazing impact injury.
Close-up of bruising and
swollen leg joint.
[BGGW Glaslyn Wildlife]

This begged the next question: could there be some underlying factor that was affecting some of these birds but not others, even though the incidents were happening in widely-separated nest locations and at different times? Powerful minds (much more powerful than mine) applied themselves to the problem. The 'usual suspects' were rounded up: provisioning rates, environmental pollutants, fungal toxins... one by one, they were eliminated from the inquiry. Exotic diseases were invoked: could it be bird flu? Avian malaria? Trichomonosis? Any of these can affect lower body function but they have other symptoms, too, none of which seemed to be present.

The leg rings themselves were checked on, and checked on again. But all were the same rings as had been used in previous years, made from the same materials and fitted by the same teams. It wasn't the rings.

Other theories were suggested, from the mildly unlikely to the just-plain-bonkers. Recessive gene mutations? Nope. Calcium deficiency causing paralysis? Can't be. Short term variations in the Earth's magnetic field? Gimme a break.

Perhaps there IS no answer. Alternatively (and it's just another theory) the answer might have been staring us in the face, all the time...

Kielder osprey Y0 fledged on 15^th July, out of

view from the nest cameras. She did not return

to the nest after fledging. Current whereabouts

unknown. [Img: Paul McMichael]

I was chatting with young Damien the other day. Damien is one of the guys on the local red squirrel conservation survey, and he gets the job of installing the higher-level trail cameras and bait trays. Part biology student and part gibbon - with vocalizations to match – Damien is not a happy arborealist these days.

“Duuude... real gnarly climbing up there... like, slippy and slidey, y'know... maaad dangerous...”  

And this is a bloke who will happily hang from a branch by the crook of one elbow while thumbing tweets into his mobile with the other hand. The boy's prehensile. If Damien thinks that working up in the trees has suddenly become “mad dangerous”, then something is amiss.

My UK readers will have noticed that, in 2016, the notorious British Summer has been even less summery than usual. Rainfall - markedly in the west and north - has produced totals for June that were 30% higher than the moving average. The figures for July are not likely to be much better. Cloud cover has been over 90% for almost 90% of the days. These unsettled conditions have featured blustery winds, variable in direction and gust strength. In technical terms, it's been rubbish.

What effect might such unseasonably poor weather over such an extended period have on the environment?
 
Wet and humid conditions are ideal for growing the algae and moss that has

been troubling our Damien. Branches of deadwood trees (exactly the ones that are favoured by ospreys for perching) never get the chance to dry out, making them slippery and even liable to breakages. Cloud cover makes for poorer visibility, more difficult judgement of distance, while gusting winds are the last thing that any fledgling bird needs to encounter on its first experimental flights.

Any one of these factors could cause a problem on its own – but put them all together and they stack: generating a persistent and cumulative rise in the accident rate that we start to notice.

And so we mustn't give in to that seditious inclination of ours: that everything that happens must have a single identifiable cause and agent, so that we can hold someone or something “responsible” before dashing off in pursuit of the next conspiracy. I find no mysterious or even sinister forces at work here. There's an underlying rough-and-tumble to any wild fledging season - and the rougher it gets, the more tumbles it produces. In certain isolated years, all the adverse factors combine in one relentless stream of bad luck and unhappy accidents.

I blame the weather – but the weather didn't mean it. All these incidents are still just Nature, doing that stuff She does.

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The views expressed in this article are those of the author himself, and are not intended to be representative of any other organization or group.

ELEVEN DEGREES WEST

UV and the passage of the Sahara

So we think that UV has commenced his return migration. His first challenge is to traverse the western desert – a 2000 km flight to reach the straits of Gibraltar. We tend to think of this as a hazardous route, and for us it would be. But for birds – not so much...

22nd April 2016: UV sets out from Senegal, catching a few thermals on the way.  (Data: Forestry Commission England) 

There are few sizeable predators, and even fewer that would be capable of taking on an osprey. There are almost no invisible overhead cables to trap the inattentive; no mad fat bastards with guns to shoot at them; no speeding vehicles to collide with them. The skies are clear and visibility is good. It's just a matter of flying.

Of course there are no fish and precious little water in a desert – but an adult osprey in the early stages of migration does not require these things. Before leaving Senegal, UV will have bulked up, laying down fat reserves as fuel for the coming journey. And as he flies northwards, his body deploys Evolution's secret weapon for long-distance migration... “ß-oxidation.”

This is part of a three-stage process whereby lipids (stored fat) are converted into energy to power UV's flight muscles. And as a by-product, metabolic water is released at the cellular level. The numbers seem like a conjuring trick: 110g of water is produced for each 100g of fat consumed! (Okay, some other stuff is going on here as well, but it's still a remarkable adaptation.)

This biological miracle is the key to long-distance bird migration: the longer and harder you fly, the more water you get!

-WlW

Further reading:http://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1941&context=etd

Evidence for communal roosting of wintering European osprey Pandion haliaetus

The breeding habits of the European osprey have been well documented over the years but, until comparatively recently, much less was known about their lifestyle at winter quarters.

UV on 26th Feb 2016 (Vic Paine)

 A combination of satellite tracking, high-visibility rings, and diligent fieldwork from many sources has increased our understanding of this seasonal behaviour, but much remains to be discovered.

In the last ten years, bird tracking devices have used on-board GPS sensors in preference to the much-less accurate doppler VHF system. This has allowed us to observe specific movements during both day and night, and some patterns have started to emerge...

It had always been thought that ospreys were mainly sedentary during the winter season, keeping to a small activity area and seldom if ever leaving it until the time for spring migration. But the higher levels of detail now available has shown that this simplistic picture is not quite right. Many ospreys - and especially those that forage along exposed beaches and river systems - leave their hunting areas for the evening and roost overnight at favourite spots further inland, often in the same tree each night. Only where there are coastal or riparian “forests” (such as mature mangrove) do they tend to remain in place.

The reasons for this behaviour are not difficult to deduce: beaches may be warm and sunny during the day but chillier at night. Vegetation tends to be low and sparse, so predation risk would be higher. Evenings along river margins are when biting insects become most active.

Many tracked ospreys, including “Ceulan” (Blue 3C in 2012) have returned tracking info that demonstrates this transference to off-area roosting. As I studied their various data files over the years, I kept asking myself the same question: why is this bird flying five, ten, even twenty kilometres to THIS roosting tree? It must have flown past hundreds of other suitable trees to get there – so what's so special about this particular roost?

When Joanna Dailey, Pip Rowe and Vic Paine visited NW Senegal [1] in February 2016, I encouraged them to pay special attention to the roost site(s) of osprey Blue UV – a 2014 osprey from Kielder Water in Northumberland. This bird was carrying a “second generation” GSM tracking device, so we knew exactly where he was sleeping and were getting regular updates each day on his diurnal movements. (I was under no illusions about what I was asking of them: night falls very quickly at latitude 16ºN, and the west African bush is no place for newly-arrived white folks to go wandering around in the dark.)

Nonetheless, the group DID manage to observe UV at his habitual roost site – and he wasn't the only osprey using it! On successive mornings, they were able to see several birds leave the area and fly westwards towards the fish-rich Langue de Barbarie coastal strip. It was exactly what I had hoped they would find.

UV leaves his favourite baobab tree in the early morning (Vic Paine)

Later, Dirk Vanhoecke (director of the Tougoupeul Project)[2], confirmed in conversation with JD that his study group regularly see numbers of ospreys - six or seven, typically - roosting together in the wooded hinterland areas of NW Senegal. In this specific case, UV appeared to be totally relaxed in the company of other ospreys: was seen preening at perch and flying with them in the early mornings. The roost was also occupied by other species, including red-billed hornbills T. erythrorhynchus kempii.

Although large birds of prey do not form daytime flocks, communal or semi-communal winter roosting has been observed in species such as Bonelli's Eagle[3] and Montague's Harrier. In recent years, migratory lesser kestrel roosts of over to 20,000 individuals have been found in west Africa [4]. The survival benefits of communal roosting suggest that ospreys should have evolved similar behaviour and, as their overall population numbers slowly recover, we are beginning to see evidence that this is so. 

An osprey flies out over the Langue de Barbarie, Feb 2016 (Joanna Dailey)

 My thanks to Vic Paine and JD for permission to use original photographs in this article.

[Links and sources...]

[1] Kielder Osprey blog:https://kielderospreys.wordpress.com/2016/03/05/langue-de-barbarie-national-park-winter-home-for-uv-and-many-other-birds/

[2] Project Tougoupeul : http://www.tougoupeul.be/

[3] Communal Roosting in Young Bonelli's Eagles (Aquila fasciata); Marcos
Moleón, Jesús Bautista, and Agustín Madero (in Spanish) : http://dx.doi.org/10.3356/JRR-11-30.1

[4] Lesser Kestrel roosting: http://www.birdguides.com/webzine/article.asp?print=1&a=992

An Osprey For All Seasons – Blue 7H

30^th October 2015

“Bad luck! If I’d any good luck to spare he could have some. I wish we could all have good luck, all the time! I wish we had wings!” [Robert Bolt: A Man For all Seasons, II,i.]

We call it the “activity counter” - and in the world of GPS-based wildlife tracking, it can be a dreadful, portentous, doom-laden thing.
The activity counter is a column of numbers in a data file. When a bird or animal is being tracked, sensors in the PTT unit record any movements between sample points, and increment this number at each occurrence. An activity count that has NOT updated within a significant span of time, brings on a feeling that is all too-familiar to wildlife researchers:-

“Oh, no – not again...” 

Whether tracked or not, the population survival statistics for sub-adult overwintering ospreys are – as with the young of many other predator species – brutal and uncompromising. Fewer than one in four ever return to their natal regions in northern Europe to breed. It's unclear if this ratio is getting worse, but it certainly isn't getting any better. Many adverse factors seem to be at work, and the renowned conservationist Roy Dennis has estimated that some 60% of losses are due to “human activities” - either directly (illegal shooting and trapping, vehicle collisions, wire strikes, and so on) or indirectly, through loss and conversion of habitat and potential nest sites. Ospreys and other raptors that survive to breeding maturity have one thing in common: 

They all had good luck, ALL of the time.

7H was fledged at Kielder in 2014.  She became special to us in the way that these things always happen: though interest and familiarity. But 7H was not a pet - she was and remained a wild, free creature, doing exactly what her nature had inclined her to do. In following her adventures and those of her kin from Kielder Forest, we were able to learn more about this nature – and at a level of detail that may not have been achieved before.

We observed her migration with bated breath, over land and sea. We watched as she caught rides on passing ships (occasionally in the wrong direction.) We saw her learn to catch fish, and how she became gradually more proficient at this.

7H was part of my study into osprey flight strategies, proving that even very young birds of this species have an innate ability to exploit the winds and thermal air currents, and to cover vast distances with the minimum expenditure of energy. She contributed to new understanding of how first-winter ospreys settle into a feeding territory, and interact with others of their kind. She even taught us how fast she could fly, and how far... 

On her initial migration from Northumberland to Morocco, 7H traversed 5188 km. This might sound like a whole lot of flying to us, but her activity in the year AFTER arrival puts this in a startlingly different perceptive:

In the ensuing twelve months, 7H's total distance flown was an additional 9500 km – all carried out within about 40km of her “home” roost locations. Clearly, our traditional view that wintering ospreys “are mostly sedentary” does not reflect how active they are on a day-to-day basis.

 Because we were “with” 7H through the full cycle of seasons, we are able to see how those seasonal changes affected her foraging behaviour. We had confirmation that ospreys will seek for, and use, different hunting areas – even when there are more than adequate supplies in just one of those areas. And in particular, a detailed analysis of 7H's favoured perches and roost sites revealed that – to an osprey – seclusion and the absence of human disturbance are much more important than scenic views or epic landscapes.

So, yes – we have learned a great deal from Blue 7H and this knowledge is important for future conservation efforts. But 7H herself would not have cared one jot for that. Instead, she spent 399 days in Africa living the life that she was born into, free and wild. For those 399 days it had appeared that she was doing everything right: she had chosen a country where wildlife protection law is regarded more seriously than it is in some less-civilized parts of the world – such as Ireland, or Scotland.

Personally, I choose not to grieve for the passing of 7H, but just to be thankful for these many insights into her unique way of life. It has been a rare privilege and one that I will not forget any time soon.

-WlW

___________________________________________________________

Joanna has written a valedictory article about 7H on the Kielder Ospreys blog, HERE

Data provided courtesy of Forestry Commission England

"Side By Side" - FR4 and VY on migration

VY and FR4 comparative migration routes – Autumn 2015

[Click for larger]

Of the entire European population of ospreys, only a tiny proportion are

satellite-tracked every season. Of these few, it's always found that the juvenile birds follow very different migration paths – for ospreys are solo travellers and each individual chooses its own direction. But HOW do they choose these routes?

This year (2015), we are tracking Blue VY from nest site #1 at Kielder Forest. She left “home” on 30^th August and made steady progress southwards, for conditions were favourable at the time. Consistent breeze from the north and good visibility are all that a young osprey requires at this time of year.

By coincidence, another (and unrelated) juvenile started its migration at almost the same time: Blue FR4 from the Scottish Wildlife Trust nest at Loch of the Lowes passed through 55ºN about one day behind VY. The latter remained “in the lead” as the birds made their way southwards – but FR4 gradually caught up, helped in no small measure by VY's evident reluctance to make early starts! By the time both were in southern Spain, their tracks had converged both in distance and time. At roost on the 8^th September, the pair were on identical courses and only 18 km apart. (Even so, they remained totally unaware of each other's existence, and would never meet.)

This unusual situation provides some insights into the factors that might influence a juvenile's choices during migration, and the most obvious of these is weather – or in this particular case, the absence of it...

With such good conditions prevailing, both ospreys were able to follow their instincts and take the most efficient and direct routes southwards. This included the “inland” route over the western Sahara desert, which is much shorter than following the African coast as many previous tracked birds had done. However, such a “routine” migration track did not cast much light on the behaviour of individuals – until, that is, the youngsters made it into southern Mauritania...

[Click for larger]

On the afternoon of the 14^th, the young ospreys encountered their first real “problem” on this migration. The rainy season in sub-Saharan Africa was well under way – and that means variable monsoon winds out of the west and slow-moving low pressure systems that track along the desert margins. One such system was over the Senegal River valley as VY and FR4 arrived, and they found that the helpful northerly winds which had borne them all the way from Britain were gone.

As a result, our ospreys had to adopt a different flight strategy and it was the same in both cases – a course alteration SE to avoid the low pressure with its rain and poor visibility. Once across the river, they were able to turn south again, then back towards the SW on the 16^th as the weather conditions improved.

It's important to understand that the birds were not being “blown off course” at any stage. They were simply adapting their route and direction to take account of the winds and other conditions at the time – just at all other times.

And this is why birds that migrate independently can sometimes follow the same path. 

Images: Google Earth
VY Data: Forestry Commission England

Dark Skies and Dancing Ospreys

“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.” 

D. Adams – The Hitch-Hiker's Guide To The Galaxy - Ch1

If Douglas Adams had ever visited Kielder Forest, the same thought might have occurred to him. At over 65,000 hectares, it's the largest working forest in England. The main crop is sitka spruce, grown in “fields” or forestry blocks on the nutrient-poor upland soil.

It's thirty years since I was last in Northumberland. I've arrived here after a long drive from Worcestershire the previous day to meet with Joanna, and also Martin the FC ornithologist. We gather at the grandiose-sounding Kielder Castle – which is actually a rather modest 18thC hunting lodge, now housing the small cafe where visitors can view video feeds from the osprey nests. The nests themselves are in remote areas of the forest, far off the tourist trails and cycling paths around the reservoir.

Kielder Water from Leaplish

Today will be a special treat, because Martin is going to accompany us up into those less-frequented areas. After spending the winter doing interpretive desk-work on the satellite tracking data, I need to get a better idea of the layout at Kielder and how the various parts of the landscape relate to each other. To this end, we have special dispensation to enter the working forest roads – which are closed to the public due to the presence of harvesting machinery and heavy transport in those areas.

At that moment someone else appears, unexpected and unannounced, and you could knock me down with an osprey feather. It's Pip Rowe – heroine of the “Search for 7H” in Morocco and all-round good person. There is a spare seat so we pile our gear into Martin's 4x4 and set out for higher ground...

From the upper track on Castle Hill, we can look down on the weir at Bakethin and the viaduct. In the distance westward is the high ground of Black Fell (379m). Last night, Joanna and I were over there at the Kielder Observatory, built in 2008 to take advantage of this specially-protected “dark sky” zone. We were supposed to be spotting auroras but cloudy conditions on the night prevented any live viewing. However, Matt and the other staff astronomers put on a good show of “let's have a look at what you would have seen”, using existing photos and graphics on the big screen.

Kielder Observatory

It's a remarkable and interesting facility, and well worth a visit if you are in the area.  

During my reverie, Martin and Joanna have been jumping in and out of the vehicle to unlock and then secure various gates. We are now well into the “operational” part of Kielder forest, with its patchwork of plantation blocks in various stages of growth. This monoculture of trees at identical heights is one reason that FC have erected nesting platforms for the ospreys (who prefer to have a good view over neighbouring timber) and also many dozens of nest boxes for the forest's population of tawny owls. We can see one of the osprey nests in the distance but there is no sign of the youngsters there. Where are they?

The track gains more altitude. A buzzard drops from a branch and flies along the track just ahead of us, giving a great close-up view before it wheels away down one of the firebreaks. The road continues with many junctions and more gates, and by now I have little remaining idea of where we are or where we're going. It's all trees. Even the redoubtable Martin seems slightly unsure of the route – this is a seldom-visited part of the forest and only the rangers come up here on their regular rounds.

We emerge under a big and glowing sky into an area of clear-fell that has been harvested and replanted. In suitable places, FC conservation staff take advantage of the heavy machinery being deployed for planting, to dig shallow ponds. These provide much-needed habitat for amphibians and insect life, and a source of fresh water on the isolated uplands. They also, it would seem, provide bathing places for young ospreys... 

Which is exactly what the young ospreys are doing, right in front of us!

The pond itself would not win any awards in a “Most Spectacular Medium-sized Pond” competition – but obviously it's a special place for the birds, and now for us. With no disturbance from walkers, no more forestry operations for the next twenty years or so, and a clear view over the surrounding landscape, ospreys can gather here in peace. As we watch, two juveniles dance and circle each other on the far side of the slope, not a care in the world between them. They are too far away to identify by leg rings, but the sight is enthralling.

Eventually the birds depart in the late afternoon and it's time for us to move on as well. I've been deliberately vague about exactly where the Pond of the Ospreys is. It will always be a special place for Joanna, Pip, Martin and me, but the location must remain secret - so that next season another generation of birds can come here, undisturbed, to bathe and circle and dance again under the dark and shining skies of Kielder.

 -Wlw
17th August 2015

 

BATHTUB BLUES (And reds)

"In birds, the emergency life-history stage is promoted by a release of the stress hormone corticosterone. However, how corticosterone reduces the expression of parental cares remains to be clarified. One hypothesis is that the release of corticosterone may also affect prolactin levels, a pituitary hormone widely involved in regulating parental behaviours” [1]

Ospreys are a long-lived species and, as such, their reproductive strategy is spread over multiple breeding seasons. In this context, the survival of the adult female is paramount. When something goes “wrong” during the early stages of nesting, female birds have a physiological response to stress hormones that can switch away from normal nesting behaviour, and back into a mode that more resembles everyday life for a non-breeding individual. The “wrongness” could be one single event – nest disturbance, sudden reduction in food supply, prolonged bad weather, or desertion by (or absence of) the paired male – or a number of events that, taken together, add up to a “wrong” situation.

This season (2015), we have seen several high-profile examples of disrupted nesting behaviour – notably at Glaslyn (non-return of the incumbent male) and at Loch Garten (incumbent male apparently evicted by intruders.)  Such events seem to be an integral part of the osprey ecology, and have probably been occurring for many millions of years. They are a necessary thing if the species is to continue in its traditional breeding range

From ref. [1]

Scientists have discovered some of the mechanisms that lead to this “emergency life-history stage”. One of them is the effect of stress-related hormones such as corticosterones on serum prolactin – the “parental behaviour” chemical that normally takes precedence during nesting.

When prolactin levels crash in an emergency life-history stage, we see the female apparently “abandoning” or “ignoring” eggs, or even newly-hatched chicks. For human observers, this action seems to be ethically and/or morally culpable, but we must not look at it this way. The female bird has no choices in the matter: without the correct circulating hormones to trigger her behaviour, she no longer recognizes the eggs, does not know what to do with them, has no interest in them at all. Nor has she really “decided” to adopt a new strategy for her own survival or breeding success at some later time – evolution has decided these things for her.

This leaves the question of how the female's behaviour can alter so quickly (or slowly) to take account of the changing situation. To find out, we need to understand the way that hormones are created in the body, how they are disposed of, and how long these processes take – a branch of science called pharmokinetics.

From ref. [1]

In birds, egg production seems to be associated with a substance called luteinizing hormone (LH) – a glycoprotein that is released from the pituitary gland. Parental behaviour (incubation and caring for young), as we have already seen, is promoted by prolactin. The relationship between LH and prolactin levels in birds is very complicated, and both circulating factors are affected by other substances. However, we do know that they can be secreted in very large quantities, when conditions are appropriate..

And it's this basal secretion rate that provides the answer to rapid behavioural changes in birds, because NEITHER of these hormones hang around in the bloodstream for very long. The “serum half-life” of prolactin (the time taken for 50% of a given quantity to be cleared) varies according to the size of the bird, but in larger raptors seems to be around 40 minutes.

Think of trying to fill a bathtub when you have forgotten to put the plug in the plughole. If the amount of water coming in through the taps is greater than the outflow, then the bath will fill eventually – but as soon as the filling rate slackens off, the water level will start to fall again. Turn off the taps completely and the bath will empty very rapidly.

This is the way that seasonal reproductive hormones act in birds: Only if the nesting situation is favourable in most respects – and remains so, will hormones be maintained at the correct level.  The existence of an emergency life-history stage is a remarkable adaptation. For birds in general, it is not an incident of failure – it is one of the long-term secrets of their success.

(Click for larger)

SOURCES:

“How does corticosterone affect parental behaviour and reproductive success? A study of prolactin in black-legged kittiwakes” F Angelier, C Clément-Chastel, J Welcker, G W Gabrielsen, O Chastel, 2009 

“Neural Circuits Underlying Parental Behavior” C Dulac, L A O’Connell, and Zheng Wu. 2014.
Neural Control of Maternal and Paternal Behaviors. Science 345,no. 6198: 765–770.