Migration within the annual cycle: species, sex and age differences

Abstract

International audienceThe three main energy-demanding events in the yearly cycles of birds--breeding, moult and migration--tend to occur at different times of year from one another, with minimal overlap. The sequence in which these various events occur varies according to the ecological conditions (including those encountered during migration) in which particular populations live, and in general, moult is more variable in timing than other events. Some migratory birds moult in their breeding areas after nesting is over, others moult at a staging area on migration, while others moult in winter quarters. Yet others show a split moult, replacing part of their plumage in one place and part in another, moult usually being arrested during the intervening migration. Split moults are often associated with split migrations, as the birds pause for several weeks on their journeys to replace their feathers. Different variants in these patterns occur in different geographical populations of the same species. Some types of birds overlap breeding and moult, and some also overlap moult and migration, especially body moult, which can occur without reducing flight efficiency. A few bird species, with short breeding cycles, have been found to nest in two different areas in a single year, separated by migration. In species in which the young are raised by only one parent, the other parent is able to begin post-breeding moult or migration at a much earlier date. In species in which individuals do not breed in their early years of life, moults and migrations are shifted into the more favourable period which in older birds is occupied by breeding. The main message of this review is the huge variation that occurs in the annual cycles of birds, in the timing and duration of different processes, the sequence in which they occur, and the degree of overlap between them. Variations occur not only between species and populations but also between sex and age-groups within the same population. It is suggested that many species remain in a state of suspended readiness for breeding, moult or migration, and can undertake any of these processes over a greater part of the year than that in which they are normally expressed. Two or more of these processes can remain in this state of readiness simultaneously, enabling the bird to suppress, advance or delay a particular process, according to the conditions in which it finds itself

Bird migration on Helgoland: the yield from 100 years of research

“…He S26 J Ornithol (2011) (Weigold 1922). His successor, Rudolf Drost (who worked on Helgoland from 1924 to 1944) further improved this trap, which is now used around the world at numerous bird observatories (e.g., Newton 2008;Archer et al 2010). Drost also increased the number of ringed birds by catching them at the Helgoland lighthouse, which attracted huge number of them on foggy and misty nights (Drost 1925(Drost , 1928(Drost , 1960.…”

“…The reasons for their occurrence are quite variable and are still not understood (Newton 2008). The occurrence of vagrants on Helgoland can, depending on the species, be explained by dispersal, wind drift, overshooting, or mirror-image and reversed-direction migration (for details see Dierschke et al 2011).…”

“…Birds are well known to be indicators of environmental change (Furness and Greenwood 1993;Bauer and Berthold 1997;Gregory et al 2009). Long-term constant-effort trapping provides an excellent data set for revealing population dynamics (Berthold and Schlenker 1975;Dunn et al 2004), phenology (Jenni 1984;Berthold 2001;Newton 2008), annual rhythms (Gwinner 1996), and the correlations between bird migration and environmental variables such as food offer, weather or climate throughout the annual cycles of birds (e.g., Berthold 1996Berthold , 2001Bairlein and Hüppop 2004;Newton 2011). Moreover, a comparative analysis of standardized long-term ringing datasets can help to unravel large-scale migration processes (Bairlein and Schaub 2009).…”

“…This also holds for the tiny island of Helgoland (or Heligoland) in the south-eastern North Sea (Gätke 1895;Vauk 1972;Dierschke et al 2011). Actually, Helgoland was the very first place on Earth to be the subject of systematic studies on bird migration (Newton 2008;Vaughan 2009;Archer et al 2010;Møller et al 2010), long before the ''Vogelwarte Helgoland'' was founded on Helgoland in 1910. However, considering that 2010 was the centenary of the Institute of Avian Research, as the ''Vogelwarte Helgoland'' has been called since its move to the mainland in Wilhelmshaven after the Second World War (Bairlein and Becker 2010), we will focus here mainly on the results of studies carried out on the island by the institute since 1910.…”

“…Remote islands along migration flyways often attract and concentrate large numbers of birds that are looking for stopover sites, but also ornithologists who are interested in bird migration, as well as lots of birders (e.g., Clarke 1912;Moore et al 1990;Pyle et al 1993;Berthold 1996;Newton 2008;Archer et al 2010). This also holds for the tiny island of Helgoland (or Heligoland) in the south-eastern North Sea (Gätke 1895;Vauk 1972;Dierschke et al 2011).…”