Date: 11/13/17 9:27 am From: Fred Vir <avtrader...> Subject: Re: [JERSEYBI] Corn Crake population increase
Got you Dom. I am with you on continuing global issues for birds. We were just talking about different aspects of the crake event.
I usually sound more like you with a more long term, carrying capacity centric and ecological examination of the birding event but many listers/birders were arriving or en route via planes, cars etc. The bird dying several hours before some of us even got on the plane or in the car that day certainly cost us all including the "community" in different ways.
My thread focus was more on the increasing chances of future Nearctic vagrancy; whether many of the western parts of Europe are a population sink is a different issue or thread. On that its similar to NJ's Grasshopper Sp. in many ways.............declining numbers for decades, grassland species, with multiple broods, high reproductive capacity, some core stable areas, heterogenous remaining breeding habitat, surrounding carrying capacity dropping, etc. In some years our Lakehurst surveys would have two hundred total birds by August while in other years we would have several hundred. NJ, outside of a few areas (Sussex, Salem, maybe Hunterdon counties) is a sink for Lakehurst birds. Successful conservation efforts, or fledgling rate in one area only results in dispersing birds leaving Lakehurst to die and likewise in Europe for crakes.
I never had any doubt that the very large and increasing numbers of crakes collectively in Eastern Europe, parts of Scandinavia and select parts of W Europe would result in a typical sink-source dynamics in many parts of Europe and the proposed NW Europe source area for vagrant Corn Crakes to the Nearctic.
Regardless vagrancy is only a derivative of breeding success PLUS immigration; vagrancy rates are often (but not always, see assortive vagrancy below) just a function of sheer, post breeding population numbers rather than how N was reached.
With an increase in absolute numbers in the proposed NW Europe source area of :
Total was 6,125 in ~ 1993 and circa 2010 surveys had 18,680 ( I added France to numbers)
This is a 305% increase in the source area I propose and a substantial absolute number increase of 12,555 birds (delta N +12,555!) in NW Europe. I will check the survey papers for flaws with time.
And who is to say that the contemporary drops and erratic population survey numbers from year to year now in W Eu aren't the result of a modern and real increase in purposeful vagrant dispersal by some number of birds? These birds do not return to the exact summer spot in W Eu since they became vagrants with some dying or dispersed to a potential better Eu area and remained uncounted in the millions of acres.
Presumably sexual dimorphic behavior, with females exhibiting natality and males exhibiting promiscuous outbreeding behavior that causes them to move up to 1,500 kilometers in a summer will result in a male skewed sex ratio in some areas. The NY bird was a male. These excess males may be the source of what we are seeing in the New World. By the way in 2012 there was the first ever Corn Crake recorded in Brazil. This makes 3 New World records in about 5 years. Assortive phenotypical migratory behavior may be caused by males not being reproductively successful in areas with limited habitat, carrying capacity and/or females. Hence innate vagrancy can happen.
I tend to lean towards some unknown frequency of genetically based vagrancy which can be expressed phenotypically when certain ecological factors exist.
tks Fred Virrazzi Secaucus
On 11/12/2017 6:52 AM, Dom wrote: > Hi Fred, > I wasn’t suggesting the LI bird isn’t a natural vagrant. It almost > certainly is. > > And it's true, Corncrakes have registered increases in around 15 of > the last 20 years. But these are increases from a very low base and > there has been little commensurate range expansion. (and by expansion > I mean repopulating areas where it has been extirpated rather than > isolated dispersal. Despite its migratory lifestyle it's a species > with high natal site fidelity). > > I can't speak much to the Eastern population, but I know from friends > involved in the Scottish census that it’s a hard bird to survey and > the numbers represent natural breeding volatility more than sustained > improvement or immigration from the east. The 2007 peak is a while > ago. For the last 3 years in the U.K we have seen consecutive declines > and we are back down to 866 calling males this year. I think there > were a lot of questions asked about the 2016 paper that put out the > +10,000 birds number. And of course the IUCN listing is heavily swayed > by the Russian population. > > Anyway. Let’s hope you’re right that we are witnessing fast adaptation > to changing farming methods! It's an interesting idea and there is > some evidence of this working with Black-tailed Godwit. > > Maybe it will with Corncrake too. > > Fingers crossed > Dom > > > On Sat, 11 Nov 2017 at 22:56, Fred Vir <avtrader...> > <mailto:<avtrader...>> wrote: > > Hello All: > > "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. >> >> >> <http://www.njbrc.com/index.php/reporting-rare-birds/><mailto:<jerseybi-request...><https://lists.princeton.edu/cgi-bin/wa?A0=jerseybi> >> >>