Nesting Success of Neotropical Migrant Songbirds in a Highly Fragmented Landscape

Abstract: Small forests in agricultural landscapes are generally thought to be population sinks where the nesting success of Neotropical migrant songbirds is too low to sustain populations. In 1996 and 1997, we assessed the nesting success and productivity of Wood Thrushes (  Hylocichla mustelina ) and Rose-breasted Grosbeaks (  Pheucticus ludovicianus ) in the Region of Waterloo, a highly fragmented agricultural landscape with 14% forest cover in southwestern Ontario. We located 154 Wood Thrush nests and 63 Rose-breasted Grosbeak nests in 26 small forest fragments (3–14 ha) and 15 large fragments (26–140 ha). We used the Mayfield method to determine nesting success. Across all sites nesting success was 51% for Wood Thrushes and 46% for Rose-breasted Grosbeaks. Nesting success and productivity rates were used in a simple population growth model that suggested that the Wood Thrushes but not the Rose-breasted Grosbeaks were a self-sustaining population. Forest size and distance of nests to the nearest forest edge (measured in five distance classes ranging from 0 to over 100 m) did not significantly affect the nesting success or productivity of either species. Brown-headed Cowbirds (   Molothrus ater ) parasitized 47% of all Wood Thrush nests and 10% of all Rose-breasted Grosbeak nests; parasitism significantly reduced Wood Thrush productivity but not that of Rose-breasted Grosbeaks. Our findings challenge the prevailing notion that small woodlots in a farmed landscape are invariably habitat sinks and offer additional incentive for habitat protection in settled landscapes where small forest fragments are often all that remain for conservation purposes.     

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite–illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption–desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite–illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R ² = 0.93, p < 0.05) between the Langmuir maximum DOC adsorption capacity (Q _max) and SSA. The Q _max value also showed a moderately strong relationship (R ² = 0.55, p < 0.05) with zeta potential (at pH 7). Q _max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.     

Horizon scanning for South African biodiversity: A need for social engagement as well as science

Ambio - A horizon scan was conducted to identify emerging and intensifying issues for biodiversity conservation in South Africa over the next 5–10&nbsp;years. South African biodiversity...