Temporal variation in bird assemblages: How representative is a one‐year snapshot?

Abstract

Bird assemblages generally are no longer regarded as stable entities, but rather as fluctuating in response to many factors. Australia's highly variable climate is likely to result in a high degree of dynamism in its bird assemblages, yet few studies have investigated variation on an inter-annual temporal scale. We compared two year-long samples of the bird assemblages of a series of highly fragmented buloke Allocasuarina luehmannii (Casuarinaceae) woodland remnants in south-eastern Australia, the first sample taken in 1994-1995 and the second in [2001][2002]. Bird densities were almost three times higher in the second period than in the first. Mean species richness also was significantly higher. Species richness of each individual site was unrelated between the two years. Minimum species turnover was 63% and was higher, on average, for migratory and nomadic than for sedentary species. Therefore, site-level bird assemblage composition was markedly different between the two survey periods and, on average, the assemblage composition of each site bore greater resemblance to those of other sites in the same year than to that of the same site in the other survey period. Most species changed substantially in their distribution among remnants between the two periods.The change in distribution of most species did not differ significantly from that expected if the species had redistributed at random among the sites. This suggests that although the remnant vegetation of the area is highly fragmented with minimal interpatch connectivity, bird movements among remnants must be relatively frequent. Interannual variability in Australian bird assemblages may be higher than is commonly recognized. In such dynamic systems, we must be cautious when extrapolating from the findings of short-term studies to longer temporal scales, especially in relation to conservation management. A greater understanding of the processes driving Temporal variation in bird assemblages 3 3 distributional patterns is likely to enable better predictions of species' responses to habitat change.

Birds in a vast arid upland: avian biogeographical patterns in the Pilbara region of Western Australia

“…Such effects are more noticeable in abundance data than in presence-absence data, and may lead to signifi cant differences at the individual site level through time, even when the overall assemblage composition does not differ signifi cantly (Maron et al 2005). No attempt was made to estimate species abundance, as reliable abundance measures require about an order of magnitude more effort to acquire and, in any case, are subject to signifi cant stochastic and other variation, particularly in arid areas (Ives and Klopfer 1997;Paltridge and Southgate 2001;Maron et al 2005;Alldredge et al 2007;Robin et al 2009). We therefore sampled for presence, not abundance, we sampled all sites at two times of year to minimise seasonal effects, and we ask questions at the regional, not local, scale.…”

“…Paltridge and Southgate 2001;Maron et al 2005), and is exacerbated by the high incidence of nomadism in the avifauna of the Australian arid zone (Davies 1984), at times resulting in massive changes in abundance at a given site (Robin et al 2009). Such effects are more noticeable in abundance data than in presence-absence data, and may lead to signifi cant differences at the individual site level through time, even when the overall assemblage composition does not differ signifi cantly (Maron et al 2005).…”

“…Paltridge and Southgate 2001;Maron et al 2005), and is exacerbated by the high incidence of nomadism in the avifauna of the Australian arid zone (Davies 1984), at times resulting in massive changes in abundance at a given site (Robin et al 2009). Such effects are more noticeable in abundance data than in presence-absence data, and may lead to signifi cant differences at the individual site level through time, even when the overall assemblage composition does not differ signifi cantly (Maron et al 2005). No attempt was made to estimate species abundance, as reliable abundance measures require about an order of magnitude more effort to acquire and, in any case, are subject to signifi cant stochastic and other variation, particularly in arid areas (Ives and Klopfer 1997;Paltridge and Southgate 2001;Maron et al 2005;Alldredge et al 2007;Robin et al 2009).…”

Insectivorous Bats and Silviculture: Balancing Timber Production and Bat Conservation

“…A typical approach uses chrono-sequences or snapshots of comparisons between different silvicultural methods or logging histories and makes the assumption that the matching of treatments is equal and evenly distributed across the same environmental niche and landscape context. Most importantly, a one-year snapshot may not be representative of temporal variation and dynamism over a longer period (Recher et al 1983;Maron et al 2005); thus, conservation plans developed from snap-shots can have limitations. Long-term studies are ideal for tracking changes to vegetation structure as forests regenerate after harvesting and how different ensembles of bats respond to these dynamics.…”

Does the reproductive season account for more records of birds in a marked seasonal climate landscape in the state of São Paulo, Brazil?

“…Surveying birds during breeding seasons is one of the most widespread rules of thumb among ornithologists as seasons have been suggested to influence the detection and density estimates of birds (Maron et al, 2005;Link & Sauer, 2007;Wightman et al, 2007). This typical approach has been poorly demonstrated in Neotropical habitats (Blendinger, 2005;Brandolin et al, 2007;Antunes, 2008;Volpato et al, 2009); in the Cerrado, for example, a tropical savanna with seasonal rainfall, only hourly counts of birds have been examined (Cavarzere & Moraes, 2010).…”