Hallo everybody,
This spring we have experienced a delayed return migration of a number satellite tracked Lesser Spotted Eagles (Aquila pomarina) (see www.satellite-telemetry.de) compared to other years. The birds started late to migrate in southern Africa, had a rather long stop-over period in Uganda/South Sudan (where they do not stop normally) and several of the tracked eagles (like many others not tracked) arrived 2-3 weeks late at the breeing sites in Germany, but also in other countries. Many of them did not breed.
The same phenomenon was observed in some other years, e.g. in 1998 (see Meyburg et al. 2007, complete English translation is available from the author), but the difference was not so extreme.
At least in NE-Namibia, part of the wintering range, has been extremely dry this year, which most probably influenced the departure. Our paper on wintering of LSEs in this area has just been publised online in J. Avian Biol. (free access).
We wonder if other researchers tracking other birds of this and other species have observed a similar situation and we also wonder if breeding success has been checked.
We also wonder if anybody has any idea what might be the reasons or how the problem could be investigated.
Best wishes
Bernd Meyburg
Hi Bernd
Our Hungarian sat tracked Red-footed Falcons did the same. My colleagues have found that during the most important migration period, there was an unusual (and strong) north-eastern wind in N Africa, which is not typical at that time of the year, at all. That delayed the RFFs. However, I am not sure if it is the case with the LSEs, as they leave earlier for the breeding site.
Hello,
The persistent easterly winds were common this spring in northern Africa and brought to Morocco, southern Spain, and even to the Canary islands, Red-footed falcons and many other Eastern migrants in high numbers (e.g. Icterine and Wood warblers). Tracking your birds, did they stopped-over for a long period after crossing the Sahara?
My best regards
We have the same case with Lesser Kestrels. They delayed this spring with the beginning of the breeding season in south Bulgaria. Also the season was not so successful for them. Imperial Eagles and Long-legged buzzards has weak breeding results too.
Spring in Malta was one of the worst I can recollect. Many species were only evident in their absence. Only a handful of species were recorded in larger numbers than usual. These mainly included cuckoos, stonecurlews and collared pratincoles. Bee- eaters, swifts and hirundines were recorded in some of the lowest numbers ever. Raptors too were recorded in low numbers except for Marsh Harriers which passed in good numbers early in the season. However low numbers where recorded later on. All other raptors were recorded in lower numbers than usual. Noteworthy is that a few odd records of raptors moving north is going on to date. These have included an osprey, a handful of honey buzzards and a couple of kestrels.
I would be very curious to know if the birds that have not shown up where they normally do were blown off course so badly that they are spending this season in other locations, or did they exhaust themselves trying to fly against the unfavorable winds and die in route?
It would be interesting to hear from people monitoring birds in South America, Caribbean and eastern North America if they are seeing some of the misplaced birds since the easterly winds could have carried the birds across the Atlantic.
Hello Bernd
North-east wind is not a good wind, as pointed by Matyas, as North-West wind is much better for soaring birds in Spring (the worst its clearly SE wind), however, NE is still not too bad!! It is not the best but alone is hardly the only reason for such a delay. Indeed, as Mike reported, was really THE WORST spring migration I could recall in my life in the whole South MEditerranean basin and N Africa, and there must be a reason for that as well as for the longer stop-over in African sites as well as for the fact that many eastern fly-way species were recorded in massively higher number in Spain than in Italy for ex. where they should have past through and where instead was the poorest year ever !!!
Odd, and I am sorry, i do not have a likely explanation for that but could only confirm that was the case for most migratory bird species, including many raptors !!
I think late migration dates, long stop-overs at unusual sites, late arrivals at breeding sites, and only a few individuals reproducing are all related to the availability of food resources necessary to meet the energy demands of survival, migration, and reproduction given the current climatic conditions. Headwinds and a lack of thermals (i.e., “unfavorable winds”) require birds to use more energy to migrate and, consequently, result in greater food requirements. Cold weather during the initial stages of the breeding cycle increases the amount of food resources necessary to meet the energy demands of both thermoregulation AND egg production. Since drought reduces the abundance of food items across entire landscapes, it restricts sufficient food supplies (i.e., resources necessary to meet minimum energy demands) to fewer sites. Thus, during drought, FEWER individuals in the population have access to adequate food resources and it can take longer for those individual birds to attain sufficient body condition (i.e., reserves) to migrate or breed.
To investigate this hypothesis, I would compare site-specific annual precipitation levels prior to migration for each year relative to the long-term historical averages on wintering, migration, and breeding sites (i.e., to identify drought years). I would also compare among years (e.g., 2015 versus 1998), average wind speed and direction during the migration period and cumulative precipitation prior to migration to quantify year-specific energy demands relative to the availability of food resources. I would expect a stronger effect of wind speed/direction on migration rates during drought years because greater food supplies are needed for individuals to migrate during “unfavorable winds”. Information on site-specific abundances of prey species per year, if you have it, can be used to identify the effects of environmental conditions on survival, migration, and reproduction. Please see my dissertation “Reproductive responses of an apex predator to changing climatic conditions in a variable forest environment” for an example of how to quantify the effects of environmental variation on raptor population processes. You can access it on my ResearchGate account under the featured publications.
There seems to be similar conditions with LSEs in NE Poland. Birds arrived rather late in many breeding sites during the last spring season. Some did not try breeding probably becouse of that as well as due to low water level and poor food conditions. Greetings from Poland, Michal Polakowski
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