Research finds birdsong trigger

Birds know to sing in the spring because of hormones triggered by longer days, researchers have found.
Teams from the Roslin Institute near Edinburgh and Nagoya University in Japan have identified how part of a bird's brain is affected by seasons.
Scientists found cells near the pituitary gland release a hormone in the spring in readiness for mating.
The bird then begins to sing more often to attract potential mating partners, the experts tell the journal Nature

Lees meer: BBC News

Do co-nesting Arctic and Common Terns partition foraging habitat and chick diets?

Auteurs: Rock, JC; Leonard, ML; Boyne, AW
Bron: WATERBIRDS, 30 (4): 579-587; DEC 2007
Abstract: We identified foraging locations during a two-year radio telemetry study (2003-2004) and described chick diets over a seven year period (1999-2005) for co-nesting Arctic (Sterna paradisaea) and Common Terns (Sterna hirundo) at Country Island, Nova Scotia, Canada. The results of the radio telemetry study showed that both species foraged within nine km of the breeding colony, however, Arctic Terns foraged in deeper water on the seaward side of the colony while Common Terns foraged in relatively shallow water between the colony and the mainland.
The results of the diet study, showed that chick diets overlapped significantly, with both species feeding mostly oil hake (Urophycis sp.) and sand lance (Ammodytes sp.). Despite the overlap in diet, Arctic Terns delivered proportionally more hake and less sand lance than Common Terns and the sand lance they delivered were smaller on average than those delivered by Common Terns. Overall, Arctic and Common terns at this site show foraging habitat segregation, but similar chick diets.

The effect of within-flock spatial position on the use of social foraging tactics in free-living tree sparrows

Auteur(s): Monus, F, Barta, Z
Bron: ETHOLOGY, 114 (3): 215-222; MAR 2008
Abstract: The benefit of producer (searches for own food) or scrounger (exploits the others' food discoveries) foraging tactic in a group of socially feeding animals may depend on where the individual searches for food within the group. Scrounging may be more advantageous in the centre of the group, having more individuals around to join, while producing may be more beneficial at the edges, where more unexplored food patches may be found.
This study shows within-flock position correlates with foraging tactic use of feeding birds in socially foraging tree sparrows, Passer montanus. Sparrows staying closer to the centre of the flock found their food patches more frequently by joining (i.e. use more frequently the scrounging tactic) than those staying toward the edges. To our knowledge this is the first field study demonstrating the relationship between spatial position and foraging tactic use.
We investigated this relationship under different perceived predation hazard, and found that under elevated risk of predation, central individuals may increase their use of joining more than individuals on the periphery of the flock. Moreover, we show that extremely specialized use of searching tactics may be very infrequent in tree sparrows. As both within-flock position and search tactic use can be altered very quickly and without leaving the flock, individuals may easily alter them in order to adjust their behaviour.

Wandering albatrosses follow their nose

The first study of how individual wandering albatrosses find food shows that the birds rely heavily on their sense of smell. The birds can pick up a scent from several miles away, U.S. and French researchers have found.
"This is the first time anyone has looked at the odor-tracking behavior of individual birds in the wild using remote techniques," said Gabrielle Nevitt, professor of neurobiology, physiology and behavior at UC Davis and an author on the study with UC Davis graduate student Marcel Losekoot of the Bodega Marine Laboratory and Henri Weimerskirch of the Centre National de la Recherche Scientifique, France.

Lees meer: PhysOrg.com

Pollutants Increase Song Complexity and the Volume of the Brain Area HVC in a Songbird

Auteur(s): Shai Markman, Stefan Leitner, Clive Catchpole, Sara Barnsley, Carsten T. Müller, David Pascoe, Katherine L. Buchanan
Bron: PLoS ONE 3(2): e1674. doi:10.1371/journal.pone.0001674
Abstract: Environmental pollutants which alter endocrine function are now known to decrease vertebrate reproductive success. There is considerable evidence for endocrine disruption from aquatic ecosystems, but knowledge is lacking with regard to the interface between terrestrial and aquatic ecosystems. Here, we show for the first time that birds foraging on invertebrates contaminated with environmental pollutants, show marked changes in both brain and behaviour. We found that male European starlings (Sturnus vulgaris) exposed to environmentally relevant levels of synthetic and natural estrogen mimics developed longer and more complex songs compared to control males, a sexually selected trait important in attracting females for reproduction. Moreover, females preferred the song of males which had higher pollutant exposure, despite the fact that experimentally dosed males showed reduced immune function. We also show that the key brain area controlling male song complexity (HVC) is significantly enlarged in the contaminated birds. This is the first evidence that environmental pollutants not only affect, but paradoxically enhance a signal of male quality such as song. Our data suggest that female starlings would bias their choice towards exposed males, with possible consequences at the population level. As the starling is a migratory species, our results suggest that transglobal effects of pollutants on terrestrial vertebrate physiology and reproduction could occur in birds.

Lees meer: PLoS ONE

Individual associations in a wintering shorebird population: do Dunlin have friends?

Auteur(s): Jesse R. Conklin, Mark A. Colwell
Bron: Journal of Field Ornithology, Volume 79 Issue 1 Page 32-40, March 2008
Abstract: Among shorebirds, many individuals make migratory and short-distance movements in large flocks, suggesting that stable social groups may persist within populations for days to months. We examined high-tide associations among individual radio-marked Dunlin wintering at Humboldt Bay, California, to determine if flocks represented stable social groups. The rate of co-occurrence of two individuals in the same flock was generally low (x = 15% of surveys), and 86% of pairs co-occurred no more than expected by chance. Associations were ephemeral, lasting 1.1 consecutive high tides on average. Variation in co-occurrence reflected individual fidelity to roosts, as well as population-wide differences in space use with precipitation and time of day. Dunlin flock composition was fluid, and individuals appeared to associate by chance according to shared attraction to common roosts. Our findings are consistent with predictions for a highly mobile, generally nonterritorial, long-distance migrant for which stable social associations have no clear benefit.

Philopatry and natal dispersal in a sedentary population of western marsh harrier

Auteur(s): Sternalski, A; Bavoux, C; Burneleau, G; et al.
Bron: Journal of Zoology 274 (2): 188-197 Feb 2008
Abstract: Dispersal is a key life-history trait because it influences population dynamics and population genetic structure. From a behavioural perspective, the study of natal dispersal requires some understanding of the mechanisms that affect individual movements, because movements of an animal form a path that is continuous throughout its life. Our aim was to investigate juvenile dispersal strategies in the western marsh harrier Circus aeruginosus, between fledging and first breeding attempt (from 1 to 4 years later, depending on the sex and individual). Using radio tracking, we monitored dispersing juvenile harriers and their home-range size variations within a sedentary population in central western France from 2001 to 2007. Juvenile dispersal strategy was mainly characterized by a very high natal philopatry (i.e. birds that remained within the study area) and short-distance dispersal. All but one bird (out of 39) remained within the study area between their first winter and their first spring, and 96.0% during their first spring. The distance moved at 2 years of age was significantly larger for males than for females (3800 +/- SD 3593 m and 935 +/- SD 481 m for seven males and six females, respectively), in contrast to most bird species studied so far. Home-range size was not sex biased and significantly decreased with age. In addition, non-breeding birds had larger home ranges (1603 +/- SD 2128 ha) than breeders (349 +/- SD 185 ha). Using data obtained from other populations, juvenile marsh harrier dispersal strategies appeared to be determined by migratory status (migratory birds dispersing farther) and demographic parameters (juvenile survival or fecundity).