Causes and consequences of spatial variation in sex ratios in a declining bird species

1. Male-biased sex ratios occur in many bird species, particularly in those with small or declining populations, but the causes of these skews and their consequences for local population demography are rarely known. Within-species variation in sex ratios can help to identify the demographic and behavioural processes associated with such biases. 2. Small populations may be more likely to have skewed sex ratios if sex differences in survival, recruitment or dispersal vary with local abundance. Analyses of species with highly variable local abundances can help to identify these mechanisms and the implications for spatial variation in demography. Many migratory bird species are currently undergoing rapid and severe declines in abundance in parts of their breeding ranges, and thus have sufficient spatial variation in abundance to explore the extent of sex ratio biases, their causes and implications. 3. Using national-scale bird ringing data for one such species (willow warbler, Phylloscopus trochilus), we show that sex ratios vary greatly across Britain, and that male-biased sites are more frequent in areas of low abundance, which are now widespread across much of south and east England. These sex ratio biases are sufficient to impact local productivity, as the relative number of juveniles caught at survey sites declines significantly with increasing sex ratio skew. 4. Sex differences in survival could influence this sex ratio variation, but we find little evidence for sex differences in survival increasing with sex ratio skew. In addition, sex ratios have become male-biased over the last two decades but there are no such trends in adult survival rates for males or females. This suggests that lower female recruitment into low abundance sites is contributing to these skews. 5. These findings suggest that male-biased sex ratios in small and declining populations can arise through local-scale sex-differences in survival and dispersal, with females recruiting disproportionately into larger populations. Given the high level of spatial variation in population declines and abundance of many migratory bird species across Europe at present, male-biased small populations may be increasingly common. As singing males are the primary records used in surveys of these species, and as unpaired males often sing throughout the breeding season, local sex ratio biases could also be masking the true extent of these population declines

Search for Rare and Forbidden 3-body Di-muon Decays of the Charmed Mesons D+ and Ds+

Using a high statistics sample of photo-produced charm particles from the FOCUS experiment at Fermilab, we report results of a search for eight rare and Standard-Model-forbidden decays: D+, Ds+ > h+/- muon-/+ muon+ (with h=pion or Kaon). Improvement over previous results by a factor of 1.7--14 is realized. Our branching ratio upper limit D+ > pion+ muon- muon+ of 8.8E-6 at the 90% C.L. is below the current MSSM R-Parity violating constraint.Comment: 17 pages, 7 figure file

A multi-region community model for inference about geographic variation in species richness

<p>Data used in the application of the multi-region community model (MRCM) to detection non-detection data collected from bird assemblages in R=8 geographically distinct areas (regions) in northern Italy. We augmented the data for all regions such that M = M_r = 200, i.e., by 200-n_r species for each region. The data file contains the following six objects: dataREG: region-specific covariates; K_tot: number of sampling occasions for each site in each region; M: total number of species in the augmented data set; nsites: total number of sites per region; nspecies: total number of observed species for each region; Yaug_tot: augmented species-by-sites-by-region detection frequency matrix.</p