Rui Borralho

Effects of prescribed fire on vegetation structure and breeding birds in young Pinus pinaster stands of northern Portugal

The effects of prescribed fire on understory vegetation structure and bird populations of Pinus pinaster stands in northern Portugal were assessed by using a synchronic sampling approach. During the spring of 1998 and 1999, 49 plots (of which 40 had been burned from 0.5 to 5 years ago) were characterised in terms of vegetation structure, surrounding landscape composition and breeding bird populations. Linear regression analysis and ANOVA were used to evaluate the effects of prescribed fire on vegetation and birds. Herbaceous vegetation showed a modal growth with a maximum development ca. 3 years after fire. Shrub development increased linearly with time since fire. Understory vegetation structure 5 years after fire was similar to control plots. Bird abundance and richness were influenced by plot variables (increased with stand age) and landscape variables (decreased with the amount of shrublands and eucalyptus stands surrounding the plot). After controlling for the effect of these variables, time since fire affected bird abundance, particularly for shrub/ground nesters. Minimum abundance occurred in the second or third breeding season after fire, possibly due to site tenacity or increased food availability. Prescribed burns did not affect bird richness. The size of the burned plots did not affect bird abundance or richness, probably because most burns were very small. Measures to increase bird diversity in these forests include maintaining other tree species and snags, avoiding the use of eucalyptus, and keeping a 5-year interval between consecutive prescribed burns in a given stand. The average size of burns could probably be increased without detrimental effects on bird populations.

Is driven transect sampling suitable for estimating red-legged partridge Alectoris rufa densities?

An omnibus procedure for Alectoris partridges density estimation is still lacking. The suitability of driven line and strip transect sampling for estimating red-legged partridge Alectoris rufa densities on mixed farmland, in southern Portugal, in March, May and July 1993 and 1994 was evaluated. Driven transect counts along a grid of dirt tracks were performed and compared to early spring territory mapping counts. Distance data sets exhibited prominent peaks near the origin, apparently caused by attraction of the birds to the tracks; nevertheless, line transect estimates computed using Fourier series models were similar to mapping counts in March of both years, as well as adult density estimates in July, but density was underestimated in May 1994. Line transect estimates were robust to the shift from individuals to clusters as sighting units, and to different grouping options, but not to data truncation. Driven strip transect estimates were computed using 10 m, 20 m, 40 m, 80 m, and 160 m strip widths. In March, estimates computed using the first three widths overestimated density and underestimated it in 1994 when the 160-m strip was used. May and July adult density estimates were not significantly different from those in March. In this study, driven line transect sampling was an efficient and accurate method of estimating red-legged partridge density on a farmland area in early spring and summer; however, further research is needed to evaluate its suitability in habitats of lower visibility, as detection models seem to require long-distance sightings to compensate for the attractiveness of tracks. Strip transects are not recommended because of the difficulty of choosing an adequate strip width for density estimation. Both methods revealed similar utility as indices of relative population abundance.

Effect of vegetation type and environmental factors on European wild rabbitOryctolagus cuniculus counts in a southern Portuguese montado

This study assesses the effect of vegetation and variables related to weather and light conditions on the efficacy of rabbitOryctolagus cuniculus (Linnaeus, 1758) counts carried out in the south of Portugal. Counts were carried out in two years using driven line transects, and correlated with vegetation type and the variables using generalised linear models. The offset was a surveyed area estimated using Distance Sampling Theory as a means of correcting for detectability bias. More rabbits were observed in dense vegetation during day-time counts and in crops during night-time counts. In 1998, day-time counts were higher with higher average daily temperatures, whilst the night-time counts were higher with higher minimum daily temperatures. In 1999, day-time counts decreased with the amount of rainfall in the previous month, and the night-time counts decreased with the accumulated rainfall in the previous two months and with the higher wind speeds. In order to increase efficacy, counts should be carried out either at dawn or at dusk during the post-breeding season, and with greater intensity in dense scrub or open vegetation with high tree cover. During the breeding season and winter, counts should be carried out after dusk and with greater intensity in arable crops.

Effects of hunting management on Mediterranean farmland birds

This study was funded by the Portuguese Foundation for Science and Technology (FCT) (PRAXIS/C/AGR/11062/1998) and by the European Commission under the 7th Framework Programme for Research and Technological Development through the project HUNT(212160, FP7- ENV-2007-1), and contributes to the project CGL2009-13029 from the Spanish Ministry of Science.