Tuesday, September 12, 2017

A Smelly Old Business

How do birds navigate over long distances? This complex question has been the subject of debate and controversy among scientists for decades, with Earth's magnetic field and the birds’ own sense of smell among the factors said to play a part.

It’s a subject discussed previously on Another Bird Blog but here's an interesting update by way of scientific experiments on an island I know very well.

In new investigations researchers closely followed the movements and behaviour of 32 Scopoli's Shearwaters Calonectris diomedea off the coast of Menorca. 

Scopoli's Shearwaters breed across the Mediterranean on Menorca, Ibiza, Formentera, Cabrera, Conillera and Dragonera. The majority of the population of Scopoli's Shearwater spend the non-breeding season in the Atlantic, including areas off the west coast of Africa and east coast of Brazil. They return to the Mediterranean in spring where they breed on rocky coasts and offshore islands, often close to or alongside Balearic Shearwaters Puffinus mauretanicus.  Hence, I see both species of shearwater when I visit Menorca in early May each year and when both are clearly visible from the shore, numbers varying with the daily weather conditions.

 Scopoli's Shearwater  - Daniele Occhiatto

Baearic Shearwater -Marcabrera [CC BY-SA 2.0], via Wikimedia Commons 

Menorca

Now, researchers from the universities of Oxford, Barcelona and Pisa have shown in a new experiment that the sense of smell (olfaction) is almost certainly a key factor in long-distance oceanic navigation, eliminating previous misgivings about this hypothesis. 

For the experiment the birds were split into three groups: one made temporarily anosmic (unable to smell) through nasal irrigation with zinc sulphate; another carrying small magnets; and a control group. Miniature GPS loggers were attached to the birds as they nested and incubated eggs in crevices and caves on the rocky Menorcan coast. But rather than being displaced, they were then tracked as they engaged in natural foraging trips. 

Study leader Oliver Padget, a doctoral candidate in Oxford University's Department of Zoology, said: "Navigation over the ocean is probably the extreme challenge for birds, given the long distances covered, the changing environment, and the lack of stable landmarks. Previous experiments have focused on the physical displacement of birds, combined with some form of sensory manipulation such as magnetic or olfactory deprivation. Evidence from these experiments has suggested that removing a bird's sense of smell impairs homing, whereas disruption of the magnetic sense has yielded inconclusive results"

"However, critics have questioned whether birds would behave in the same way had they not been artificially displaced, as well as arguing that rather than affecting a bird's ability to navigate, sensory deprivation may in fact impair a related function, such as its motivation to return home or its ability to forage. Our new study eliminates these objections, meaning it will be very difficult in future to argue that olfaction is not involved in long-distance oceanic navigation in birds."

All birds went out on foraging trips as normal, gained weight through successful foraging, and returned to exchange incubation periods with their partners. Thus, removing a bird's sense of smell does not appear to impair either its motivation to return home or its ability to forage effectively. However, although the anosmic birds made successful trips to the Catalan coast and other distant foraging grounds, they showed significantly different orientation behaviour from the controls during the at-sea stage of their return journeys. 

Scopoli's Shearwater - Martin Garner

Instead of being well-oriented towards home when they were out of sight of land, they embarked on curiously straight but poorly oriented flights across the ocean, as if following a compass bearing away from the foraging grounds without being able to update their position. Their orientation then improved when approaching land, suggesting that birds must consult an olfactory map when out of sight of land but are subsequently able to find home using familiar landscape features. 

Senior author Tim Guilford said: "To the best of our knowledge, this is the first study that follows free-ranging foraging trips in sensorily manipulated birds. The displacement experiment has rightly been at the heart of bird navigation studies and has produced powerful findings on what birds are able to do in the absence of information collected on their outward journey. But by its nature, the displacement experiment cannot tell us what birds would do if they had the option of using outward-journey information, as they did in our study. This heralds a whole new era of work in which careful track analysis of free-ranging movements, with and without experimental interventions, can provide inferences about the underlying behavioural mechanisms of navigation. Precision on-board tracking technology and new analytical methods, too computationally heavy to have been possible in the past have made this feasible."

Story Source: University of Oxford. "Sense of smell is key factor in bird navigation, new study shows." Science Daily, 29 August 2017.

Linking today to Stewart's World Bird Wednesday.



Wednesday, September 6, 2017

Change Of Plan

The forecast for Wednesday was decidedly “dodgy” but with it being the best for several days ahead, we decided to chance a ringing session up at Barnacre. The problem was when I got up at 0530 and looked out of the window the trees were wafting around so I sent Andy a text and said I’d go birding instead. 

I was early so stopped at Pilling Lane Ends to count the Little Egrets at the roost. Thirty-five was my total but I suspect many were hidden from view in this so called “amenity area” that is now just a neglected wilderness. 

At Braides Farm - 80+ Curlews and a roosting Buzzard. 

At Conder green Once again Lapwings proved the most numerous bird with at least 240 scattered around the site, on the island, the grassland and in the tidal creeks. Other waders were few and far between with just handfuls of Curlew, Redshank, and a single Common Sandpiper. Fishing the pool was a single Goosander, 4 Cormorant and 4 Little Egret. Two Little Grebe have moved to the creeks where I also found 8 Teal. 

Lapwing

Little Egret

It was on a circuit of Jeremy Lane that I stopped to look through a flock of 600-800 Black-headed Gulls. Almost on cue I found an adult Mediterranean Gull I had hoped to see. There have been lots of “med gulls” sighted along the coast in recent weeks and the best way to find one by searching through flocks of Black-headed Gulls. While it’s nice to see one, the “med gull” is no longer a rarity. 

Mediterranean Gull - adult winter by M. Jackson, Mull Birds

The Mediterranean Gull is the most recent addition to the species of seabirds breeding in the UK. By 2010, there were over 600-700 nesting pairs, mostly on the south and south-east coasts of England. 

The range of the Mediterranean Gull expanded markedly over the last 50 years. A westward expansion started in Hungary, where it was breeding regularly by 1953, then into Germany and Belgium during the 1960s and the Netherlands by 1970. Range expansion also occurred in an eastward direction during the 1970s and 1980s. The first breeding occurrence in Britain was in 1968, at Needs Ore Point (Hampshire). Thereafter, a pair bred at Dungeness (Kent), in 1979, increasing to two pairs by 1985. A site in north Kent was colonised in 1983, which later became established as one of the major colonies in England. Also during this period, a handful of other breeding attempts were made, including pairings with Black-headed Gulls.  

I wasn’t finding much around Jeremy Lane until I stopped to watch a Kestrel hovering over the footpath at Cockersands. There was a Marsh Harrier again, this one hunting the fields behind the old abbey, seen off in turn by Carrion Crows and Lapwings. After a while the harrier did a disappearing act, something they are good at for such a large bird. 

Marsh Harrier and Lapwings

I stopped at Gulf Lane where I dropped seed at the Linnet field and did a spot count for the week of about 100 finches - 50/50 Linnet/Goldfinch again. The weather forecast for the week ahead, wind above 15mph every day, will put paid to plans to ring any time soon. A couple of Stock Doves have found our food drop. 

Stock Dove

I was on the way to Knott End to grab some shopping but stopped along the promenade to watch the incoming tide. Recent days have seen good numbers of Sandwich Terns roosting on the sands at high tide, migrant terns that feed in Morecambe Bay while passing through the area on their way south to winter off West Africa. My minimum count was 250 with many roosting for a short period and then as the tide arrived, flying off over the jetty, south-west and up the River Wyre. 

Sandwich Terns

Sandwich Terns

 Sandwich Tern

Sandwich Tern - Range by CC BY-SA 3.0 Wiki 

Knott End Ferry

 Back soon with more birds on Another Bird Blog.  In the meantime I'm linking to Eileen's Saturday Blog.


Saturday, September 2, 2017

Some You Win

The weatherman kindly told us that Thursday 31st August was the Meteorological End of Summer. I tried to recall more than a handful of summery days during of May, June, July and August that resembled summer but I quickly gave up. 

Friday 1st September. I took a flying visit to Conder Green where a distant Kingfisher proved the only bird of note as it dived into the now shallow water from the top of the marker post. Otherwise there was the usual fare – An increase to 17 Teal, 9 Little Grebe, 80 Lapwing, 5 Snipe, 1 Goosander and 1 Common Sandpiper. The female Tufted Duck is reduced to just three youngsters now. A few pairs of Tufted Ducks have bred on the pool for the last three years but always struggle to get more than one or two youngsters up to full size. 

Kingfisher

Tufted Duck

I was on the way to Gulf Lane to unload a bucket of rape seed into our net ride in preparation for a ringing session on Saturday. The seed is back-up to the natural food that the 300+ Linnets and Goldfinch now target because those large numbers of birds will soon make a large dent in natural food availability. 

Saturday 2nd September dawned misty but bright with the promise of sun and little wind for our ringing. I met up with Andy at 0630 just as the sun rose over to the East. 

Pilling sunrise

Looking West at Pilling

Unfortunately the Linnets didn’t perform as well as have come to expect and we ended up with a meagre catch of just five birds, a total quite unlike our catches to date this autumn.  Howver, all is not lost as those five bring us to 150 newly ringed Linnets so far this autumn.

Linnet

The composition of the flock has changed considerably this week with now something like 50/50 Linnet/Goldfinch and just 200 birds in total this morning. Given the natural abundance of food at this time of year, both on site here and in the local area, the birds have many choices of where to feed. Additionally, the preferred feeding patch on site is some way from our single 80ft cut through the crop. 

We have seen a Sparrowhawk on at least three recent spot visits which leads us to think the hawk is a very regular visitor and may be deterring the finches from their usual habits. As Sparrowhawks are liable to do, once they find a reliable source of food, they come back time and time again. The hawk made two visits today, once trying to snatch a Linnet in the air and then later, moving along the fence line from where it could wait to pounce. The hawk flew off when I walked along the road towards its lookout post. 

Sparrowhawk
 
Some you win, some you lose and it won't stop us trying again soon.

We may not have had the biggest catch of the year but it was certainly good to be out in the sun for a change. 

Linking today to Stewart's World Bird Wednesday.


Related Posts with Thumbnails