The thresholds below which there will be impact of cold weather upon the hatching success of birds is not clear to me. what is also not clear to me and I cannot locate relevant literature is the following: in what ways can a few colder days affect the incubation time, the hatching and so on of birds. additionally, i cannot find informative literature on the clues used by the incubating birds to "realize" that their eggs will not hatch for example. I am sure I want a lot but that is the question. In our case we have a bird species that starts to lay eggs one month and more earlier than it did 30 years ago. But the last few years we see that the eggs of the very early nesters do not hatch. we do not know where to attribute this phenomenon. it is a colonial species and we have never watched mass abandonments.
This is happening in Greece and the species is the Dalmatian pelican Pelecanus crispus.
The following are not based on any specific experimentation, but rather on several years of studying and observing the specific species : a) low temperatures may prompt a bird which is sitting still and incubating, to stand up, or to stand beside the nest temporarily in order to "warm up" (by moving, flapping its wings etc) thus leaving the eggs exposed more often. b) Cold may influence nesting D. pelicans indirectly, by imposing to mate A lengthier than usual foraging bouts in search of less retrievable prey (fish), thus leaving incubating mate B exposed to situation (a) described above for longer periods. c) I do not know if pelicans have any clue whether their embryo is alive or not, but when they roll their eggs over -which they do frequently during the day and for the entire incubating period- they might detect differences regarding the changing "status" of the interior of the egg. For certain, during the 2 days prior to hatching, the chick emits vocalizations to which the adult apparently responds. Hope theses thoughts have been somewhat useful.
Dear Giorgios,
Yes, the Dalmatian Pelicans from the Danube Delta area also start to nest in February, probably more earlier than few decades ago. Actually, during the winter several specimens stay in this region (so, practically, they do not migrate). I have to check out if there are any information available on the difference in the rate of hatching in the present and in the past, but the size of the population is at about the same in the last decades so it is difficult to detect if an earlier egg-laying in a warmer period has as result the decline of the population...
Best regards!
Thanks Dionyssia for confirming our own observations and way of thinking about the problem. I also thought in the same thinking line. Thanks again this is valuable.
Zsolt thank you so much about your answer. Are there any data on breeding success or breeding performance in general of the DPs in the Danube Delta. it would be extremely interesting and useful for me to know these data! Thanks again
Hi Kenneth, yes this is exactly one of my questions that has to do with the effect on the bird biology.How much a difference in temperature must be in order to be considered as one having a real effect? and the same holds true for the fish. Is statistical significance (at,lets us say, 5% level) something we can argue that it might make a difference? I really do not know how much the water temperature must be warmer in order for the fish to change behaviour and start being significantly more available to pelicans.
Dear Giorgios,
May be we should think about a future project focused on the DP issue. As You can see in some posts above, Dr. Towe was referring to some aspects of interest for (at least ) one potential proposal and I am surely up to develop a partnership on this (mostly, thermal-biology related) issue.
Best regards!
08.08.2015
Zsolt
Hi Zsolt,
we are really very much interested for a collaboration on this issue with you and it would be great to start sharing ideas about it. Please write to me at [email protected] It would be great to hear your views on this and similar issues on the conservation of pelicans and your availability on joint projects. Thanks a lot indeed!
Giorgos
Hi Giorgos,
It's not for Pelicans but this might give some feedback
http://onlinelibrary.wiley.com/doi/10.1111/ibi.12351/epdf