Breeding failures are regular for the Black stork not just in Latvia however it is more and more frequent events particularely here. In fact webcam fans have been unbeliewably happy (not knowing that) the previous year when more than 60% (no error, SIXTY) of nests were un-productive.
From the diagram you can see that there are alwys some nests that do not succeed whetever the reason for that. No individual is immortal and even experienced birds die some day. That is a natural event and one should not worry about death of experienced birds. We must worry however about lack of offspring. There are no juveniles to replace disappearing adults.
The causes? Statistically the most significant one is forestry caused disturbances. It expreses in nest trees being cut, surrounding forests being cut, disturbances at foraging grounds (not allowing to collect enough food) and so on. The fact that this nest particular is peaceful is very misleading. Then there is a shortage of food. Despite hundreds of thousands of forest streams in Latvia wich used to be full of fish, there have been years when as may as 1/3 of ALL juveniles are starwing. One such year was the previous one and the fact that both juveniles in this webcan nest were well fit is a true wonder! Poor condition almost certainly means no success during the 1st migration. Birds "play" their life as "trial and error" game. Everybody is given 0 chance for errors. Once you make one - be it wrong foraging location, wrong route etc., you are finished. Mortality during th 1st year of life is larger than 80%. It has been so perhaps since "start of the time", however, the problem is the low number of chicks that enter this game. If 1000 do every year, 200 would survive, if only 100 do, only 20 reach the second year of life with the same level of mortality. Poor condition can be caused also by (lack of) quality of food, not just by absence of it. Hundreds of different pesticides, fertilisers, washing liquids etc. enter waters, accumulate in fish (some of them kill amphibians) and so affect storks. It could be even radiation caused mutations that add to this basket. Storks from Latvia (particularely so from eastern part of the country) cross contaminated zone of Chernobyl on every migration. This is just a hypothesis but very likely one - so far attempts to study it have failed as (funding) authorities are not interesed in it. Chernobyl is far away and storks here - insignificant. On top of that is ever increasing pressure of predators - pine marten, goshawk and white-tailed eagle. Also this is strenghtened by forest fragmentation. Birds tend to move away afer most cases of depredation however ofter there is no place to move to. Good ones are occupied, unknown ones are often logged. This might explain sudden appearance of a pair well after they should have had their breeding ongoing...
All that said - there is no way we can explain what and WHY happens with each particular nest (excepf for the case if it is logged - then other aspect's don't matter anymore). Birds are not "mechanical toys". They are inteligent, they have emotions, they have attitudes towards partners and strangers. Some couple like each other some just live together because there is "no one better around". What happens when someone better suddenly appears? We have seen some of this last year and might expect something of this "opera" also this year. Birds as SO human in most of their appearnces that we would not beliewe how similar (socially) we are. Legends about suicidal swans once the partner is lost and "pairs for life" are nice fairy-tale stories but they are as close to real life as fairy-tales are. Humans pretend to form "pairs for life" too. How many of those do you know? Perhaps some and so it might be also among birds. Majority? You know.
And the last but not the least. PLEASE STOP naming all BS males Ozols and all females Zīle! It is just as if we would use the name "Abraham Lincoln-2017" instead of the name of current gentleman in his place. I guess Lincoln would turn in his grave if he could. ALL birds differ individually just as we do, the problem is - they are of different size than we are and so are the differences. Plus - bird plumage, the feathers give their appearnce another dimension that we are missing. This is particularly so for the black stork with reflective colors (green and purple) changing from the angle of light and intensity of sunshine. So we might interpret as differences false effects what are not any differences at all. Intensity of this "shine" is affected also by the birds internal condition (and so might be affected if he or she is contaminated or so). Additional problem is that the wide-angle lens of the camera pictures birds so as if they would be "far away" although the center of nest is hardly 1m from the camera. All birds in fact have dull brown head coverts. Obviously brown head (so also in sunlight!) is indication of (young) age however we do not know yet at what age it disappears or looks not so brown anymore. A comparison with humans - some get the first gray hair when they are 30, some don't when they are still 70... Can you tell from the presence of gray hair the age of that person? From the very beginning I considered it be a rather silly idea to give names to individuals one cannot distinguish with certainty, but once it was done, the names must have meaningful use! There is a good reason to beliewe that the male is the same (although I'm not certain) so let ir be Ozols. However the initial Zīle is not here anymore for sure (may be already the last year, but 100% so this year!), so please stop using this name! We have far more than one name for girls in Latvian! Birds are not car models and even those are not named Peugeot-2015, Peugeot-2016 etc....
How to tell them apart? The best chance to distingush birds individaully lies in their plumage. Feathers are moulted on a regular basis during the entire liftime of birds. For the Black stork worn feathers reflect light less and look plain brown, fresh are more "shining". This can be seen fairly well in certain light conditions from aside and particularely when birds land or strech their wings. This is true for all feathers but given the size of picture we can get and distance to the object, only large wing feathers and tail feather matters. The pattern of primaries, secondaries and large coverts (1st row abowe primaries and secondaries) on each wing form a perfect bar code that is individual for each bird at least during any given season. How it differs between the seasons is a work to be done, but this could be done using only birds wich can be distinguished individualy by other means - namely only ringed (or othervise tagged) individuals.
Sex differences. There are some but in this distance and quality of pictures we can see, they are seldom visible and changing light may confuse the things even more so I will not even mention them. Behaviour is a better key. Male(s) almost always call when they land in nest (greeting with nest, perhaps), females do it(?) very seldom if the nest is empty, cannot say with certainty, if they don't. Each bird tend to have their own flight route(s), roosting sites and somtimes simply (useless) odd habits - such as Ozols fighting the small branch in the upper left corner of the frame. I think this branch simply annoys him... It is a pure guess of mine and I might be totally wrong of course.
That's "in brief". Just the next time when somebody want's to know what excatly have I said, please ask directly to me!
Enjoy watching
Maris Strazds
