Adulterous Male Birds Don't Put Eggs in One Basket

Males that stray from the nest for adulterous adventures may leave an opening for their mates to cheat, new research on great tit birds suggests.

While these absentee males end up with more adopted chicks from the female mate's flings, they also leave their own offspring in other nests. On average, the "bold" males have the same number of chicks as males who stay home.

Lees meer: LiveScience

Monogamy Helps Geese Reduce Stress

With monogamy so uncommon in the animal world, the idea of lifetime fidelity can seem a little strange, at least to evolutionary biologists.

But in greylag geese, which can live for 20 years and share those years with just one mate, biologists have found a benefit: stress reduction. During fights, males with mates have lower heart rates than their single brethren. If their partners are nearby, they’re even more relaxed.

Lees meer: Wired Science

Delayed autumn migration in northern European waterfowl

Auteurs: Aleksi Lehikoinen, Kim Jaatinen
Bron: JOURNAL OF ORNITHOLOGY, DOI: 10.1007/s10336-011-0777-z
Abstract: Climate change is causing phenological shifts in the environment. Among birds, increasing temperatures have been shown to advance the spring migration and breeding, which in turn affect individual reproductive success. The autumn migration phenology has, however, been largely overlooked. Here, we study long-term changes in the timing of autumn migration in 15 northern European waterfowl species during 1979–2009. We hypothesised that waterfowl should delay their migration since they winter north of the Sahara desert. Our results show that 6 (Greylag Goose Anser anser, Eurasian Wigeon Anas penelope, Eurasian Teal Anas crecca, Tufted Duck Aythya fuligula, Velvet Scoter Melanitta fusca, and Common Goldeneye Bucephala clangula) of the 15 studied species have delayed at least one of the three phases of migration examined. The most marked delay in median migration dates was by more than a month over the past 31 years. Only the Bean Goose Anser fabalis exhibited an advanced beginning of its migration. We also analyse the timing of the entire waterfowl migration and show that the median and end of the migration have been significantly delayed. The results support our predictions and highlight how rapid phenological responses to climate change may be. Such delayed departures may be the cause for recently observed northward shifts of wintering ducks. Our results suggest that waterfowl to be a good indicator group for climate change. Changing migration times can also have population-level consequences due to differential hunting and natural predation pressures over the waterfowl flyway.

Individually tracked geese follow peaks of temperature acceleration during spring migration

Auteurs: Rien E. van WIjk, Andrea Kölzsch, Helmut Kruckenberg, Bartwolt S. Ebbinge, Gerhard J.D.M. Müskens, Bart A. Nolet
Bron: OIKOS, Article first published online: 8 NOV 2011, DOI: 10.1111/j.1600-0706.2011.20083.x
Abstract: Many migratory herbivores seem to follow the flush of plant growth during migration in order to acquire the most nutrient-rich plants. This has also been hypothesized for arctic-breeding geese, but so far no test of this so-called green wave hypothesis has been performed at the individual level. During four years, a total of 30 greater white-fronted geese Anser albifrons albifrons was tracked using GPS transmitters, of which 13 yielded complete spring migration tracks. From those birds we defined stopover sites and related the date of arrival at each of these stopovers to temperature sum (growing degree days, GDD), snow cover, accumulated photoperiod and latitude. We found that geese arrived at spring stopovers close to the peak in GDD jerk; the ‘jerk’ is the third derivative, or the rate of change in acceleration, and GDD jerk maxima therefore represent the highest acceleration of daily temperature per site. Day of snow melt also correlated well with the observed arrival of the geese. Factors not closely related to onset of spring, i.e. accumulated photoperiod and latitude, yielded poorer fits. A comparison with published data revealed that the GDD jerk occurs 1–2 weeks earlier than the onset of spring derived from NDVI, and probably represents the very start of spring growth. Our data therefore suggest that white-fronted geese track the front of the green wave in spring.

Adaptive significance of permanent female mimicry in a bird of prey

Auteurs: Audrey Sternalski, François Mougeot, Vincent Bretagnolle
Bron: BIOLOGY LETTERS, Published online before print November 9, 2011, doi: 10.1098/rsbl.2011.0914
Abstract: Permanent female mimicry, in which adult males express a female phenotype, is known only from two bird species. A likely benefit of female mimicry is reduced intrasexual competition, allowing female-like males to access breeding resources while avoiding costly fights with typical territorial males. We tested this hypothesis in a population of marsh harriers Circus aeruginosus in which approximately 40 per cent of sexually mature males exhibit a permanent, i.e. lifelong, female plumage phenotype. Using simulated territorial intrusions, we measured aggressive responses of breeding males towards conspecific decoys of females, female-like males and typical males. We show that aggressive responses varied with both the type of decoys and the type of defending male. Typical males were aggressive towards typical male decoys more than they were towards female-like male decoys; female-like male decoys were attacked at a rate similar to that of female decoys. By contrast, female-like males tolerated male decoys (both typical and female-like) and directed their aggression towards female decoys. Thus, agonistic responses were intrasexual in typical males but intersexual in female-like males, indicating that the latter not only look like females but also behave like them when defending breeding resources. When intrasexual aggression is high, permanent female mimicry is arguably adaptive and could be seen as a permanent ‘non-aggression pact’ with other males.

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