Date: 11/11/17 2:57 pm From: Fred Vir <avtrader...> Subject: [JERSEYBI] Corn Crake population increase
"Corncrakes are suffering huge declines in most of western EU"
Perhaps more than a verb tense issue (are declining vs. were declining) it would be pertinent if we actually disagree on absolute population numbers and trends after looking at the data. Related we should agree to the actual pertinent area of Europe to nearctic vagrancy of the Corn Crake.
The declines were suffered in almost all European pops many decades ago up until the 1990s and data shows the drops are now negligible in many areas with some remaining populations seeing strong increases. There has been a collapse of collective farming methods in E. Europe; pop increases of hundreds of thousands of birds there has caused dispersal of birds to some parts of W and NW Europe but not all. Recent telemetry shows males dispersing for second brood attempts up to an amazing 1,500 Km in one season. The pop trend is up nicely in the last 25 years especially if we ditch the Western Europe moniker and more accurately agree that the Iberian Peninsula is less important a potential nearctic vagrant source than Scandinavia.
The source area would then be UK, Ireland, France, Norway, Sweden and Finland = "NW Europe".
The pop in the UK recently increased from 480 calling males in 1993 to 1,245 in 2007. In Ireland there have been double digit percent increases recently. Their numbers increased from 100 birds to 230 in a few years. Norway 1995 ~ 65 birds to 160 in 2007. In Sweden 1993 1,000 birds to est average of 600 birds in 2009. In Finland the increase was 500% from 1990 to 2008. There could now be over 14,000 birds there up from ~2,800 25 years ago. In 1998 in France, on IBAs only, there were 1200 males in 1998 with the population seeming about the same now.
year ~ 1993 or later ~ 2010
UK 960 2490 Irel 100 230 Nor 65 160 Swe 1000 600 Finl 2800 14000
total 4925 17480 350% increase in the source area I propose
Two recent Mid-Atlantic US records in the last ~ 22 months (NY, PA) after basically a gap of several decades gives some hope and a possible corollary to increasing NW Europe pops. Yes its a small data set but still perhaps statistically significant. And if two birds were found there were likely more in the last 24 months in the USA.
Admittedly changing/stronger weather patterns can be causal and/or additive.
Conservationists have advised European farmers of optimal "crake friendly cutting dates" and have had some success in getting farmers to cut from the middle of a field out, killing less birds. The crake can have up to three clutches and has tremendous breeding capacity with a little help. That help arrived several years ago with the results translating to 12,500 more birds in NW Europe now than ~ 25 years ago. This is a 350% population increase.
Deforestation in Africa is said to favor wintering crakes so the opinion is there are negligible wintering ground issues.
Globally the species has also been found to be more numerous than thought or increasing in parts of Western Europe, Eastern Europe, Russia and W China. The species has recently changed from Near Threatened to Least Concern status (IUCN).
tks Fred Virrazzi Sec NJ
On 11/11/2017 7:52 AM, Dom > Corncrakes are suffering huge declines in most of western EU. I have > yet to find one in my home country despite them breeding here. > I also suspect as afro-palearctic migrants they would probably exhibit > higher nearctic vagrancy if the population was stable. Historic US > records suggest this too. > > > > On 11 November 2017 at 12:11, Fred Vir <avtrader...> > <mailto:<avtrader...>> wrote: > > Several questions/comments were received about the crake. > > I was also thinking about two of the questions. > > "When did the bird die?" > > It seemed to have died at least several hours before before we > found the bird. Rigor seemed to have already been passed when the > bird was found. The birds plumage and eyes were looking old and > matted. And many birders were there for awhile before sunrise on > the subject day and should have seen the collision. > > "As someone who's been watching birds and clearly studying them at > length...... do you believe that this bird was indeed a European > vagrant, and not an escape from a domestic game farm? " The > question went on with good points arguing that this crake was not > as timid as the literature and observers say. > > I don't think this species has been domesticated. Regardless I > have seen scores of wintering crakes/rails of various species in 4 > continents and even nocturnal species make diurnal appearances > (Corn Crakes are diurnal). Diurnal crake spp in SA and Africa can > be seen almost daily, at will, in many areas especially in winter > as they dart in and out of cover. > > Some Corn Crakes have recently been observed entering houses via > open windows to feed and feeding out of farm pet bowls. > > This was an underweight individual; certainly hormonal signals > that synchronize migratory phenology cause animals to feed > aggressively when reserves are physiologically detected as being > low. The bird was ~ 20 to 50% underweight. In animals an urgent, > innate need for food will often incrementally result in reduced > wariness. Remember this bird saw the ocean and may have innately > been forced to make a stand to feed at that location or go > N----terrestrial predators and cars be damned. > > Observers of this crake, including me noted that it was both wary > of quick movements by people and larger vehicles. Additionally > with prior points the strip of bluestem grass may have had more > accessible insects that the shrubs; the bird was demonstrating > optimal feeding strategies. > > Also this bird showed up right on time for a putative, natural > vagrant. > > Just when you are about to agree that the bird showed reduced > wariness for the above reasons I can slightly switch to your side > but disagree with causality (domestication caused the change in > behavior rather than rapid microevolution). > > Going out of the box-------there may have been a recent, rapid > change in the genome of this species that makes it slightly less > wary. Its pre-agricultural/mechanized agricultural behavior was to > move deeper into fields when danger/noise was detected. Its > wariness was a partial cause of its industrial age decline. > Circling combines starting at the perimeter of a field would mass > the birds in an ever smaller central, circle of grass. This led to > great mortality via poised shooters or the combines....except for > which birds?----- The birds that flushed into more open areas out > of the high grass. > > If you are right about it being a bit less wary than old > literature .....could we be observing microevolution? > > tks > > Fred Virrazzi > Sec NJ > > > How to report NJ bird sightings: see > <www.njbrc.com/index.php/reporting-rare-birds/ > <http://www.njbrc.com/index.php/reporting-rare-birds/>> > or e-mail to <njbrcreport...> <mailto:<njbrcreport...> > List help: <jerseybi-request...> > <mailto:<jerseybi-request...> > List archives: https://lists.princeton.edu/cgi-bin/wa?A0=jerseybi > <https://lists.princeton.edu/cgi-bin/wa?A0=jerseybi> > >