Large decline of birds in Sahelian rangelands due to loss of woody cover and soil seed bank

Zwarts, Leo; Bijlsma, Rob G.; Kamp, Jan van der

doi:10.1016/j.jaridenv.2018.01.013

Cited by 29 publications

(49 citation statements)

References 22 publications

(36 reference statements)

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“…Over the course of the study period , the amount rainfall in the Sahel increased from the 2000s onwards, following three decades characterised by severe droughts at the end of the 20th century. This climatic shift, also called 'Sahel greening', has led to an enhanced primary production in the area (Olsson et al 2005, Dardel et al 2014b), although concurrent changes in land use and vegetation communities affect bird guilds differentially (Zwarts et al 2015(Zwarts et al , 2018. Overall, environmental conditions during the whole annual cycle were thus more favourable (slightly higher average values for the wintering period), and especially less variable (reduced among-year variation in both breeding and wintering conditions) for harriers in ML (1999ML ( -2016 than for harriers in RO (1988RO ( -2005.…”

Section: Survival Response To Environmental Variabilitymentioning

confidence: 99%

Disentangling the effects of environmental conditions on wintering and breeding grounds on age‐specific survival rates in a trans‐Saharan migratory raptor

Millon

Danovaro

Printemps³

et al. 2019

Journal of Avian Biology

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Migratory species are subject to environmental variability occurring on breeding and wintering grounds. Estimating the relative contribution of environmental factors experienced sequentially during breeding and wintering, and their potential interaction, to the variation of survival is crucial to predict population viability of migratory species. Here we investigated this issue for the Montagu's harrier Circus pygargus, a trans‐Saharan migrant. We analysed capture–recapture data from a 29‐year long monitoring of wing‐tagged offspring and adults at two study sites in France (Rochefort‐RO and Maine‐et‐Loire‐ML). The study period covers a climatic shift occurring in the Sahel with increasing rainfall following a period of droughts (Sahel greening). We found that harriers’ adult survival in RO (between 1988 and 2005) varied over time and was sensitive to the interaction between the amount of rainfall in the Sahel and the annual mean breeding success, two proxies of prey availability. The occurrence of adverse conditions on breeding and wintering grounds in the same year decreased survival from 0.70–0.77 to 0.48 ± 0.05. Juvenile survival in RO was slightly more sensitive to conditions in Europe than in the Sahel. Unexpectedly, lower survival rates were found in years with higher mean breeding success, suggesting compensatory density feedbacks may operate. By contrast, adult survival in ML, monitored between 1999 and 2017, was higher compared to RO (0.76 ± 0.03 versus 0.66 ± 0.02), remained constant and unaffected by any proxy of prey availability. This difference seems consistent with the fact that harriers in ML experienced better and especially less variable environmental conditions during breeding and wintering seasons compared to RO. Overall, we showed that survival of a migratory bird is sensitive to the level of variability in environmental conditions and that adverse conditions on wintering grounds can amplify the negative effects of conditions during the previous breeding season on birds’ survival.

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Section: Survival Response To Environmental Variabilitymentioning

confidence: 99%

Disentangling the effects of environmental conditions on wintering and breeding grounds on age‐specific survival rates in a trans‐Saharan migratory raptor

Millon

Danovaro

Printemps³

et al. 2019

Journal of Avian Biology

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“…S4 C ), indicating that record rainfall deficiencies (up to 75 to 90% below average) were likely the primary driver of mortality. The main exception to this was the catastrophic decline of passerine and some predatory bird populations in central eastern Queensland, which was observationally linked in part to reduced availability of grasses, seeds, and small prey (60), consistent with the response of avian assemblages to drought and livestock overgrazing elsewhere (61).…”

Section: Resultsmentioning

confidence: 98%

Historical reconstruction unveils the risk of mass mortality and ecosystem collapse during pancontinental megadrought

Godfree

Knerr

Godfree

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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An important new hypothesis in landscape ecology is that extreme, decade-scale megadroughts can be potent drivers of rapid, macroscale ecosystem degradation and collapse. If true, an increase in such events under climate change could have devastating consequences for global biodiversity. However, because few megadroughts have occurred in the modern ecological era, the taxonomic breadth, trophic depth, and geographic pattern of these impacts remain unknown. Here we use ecohistorical techniques to quantify the impact of a record, pancontinental megadrought period (1891 to 1903 CE) on the Australian biota. We show that during this event mortality and severe stress was recorded in >45 bird, mammal, fish, reptile, and plant families in arid, semiarid, dry temperate, and Mediterranean ecosystems over at least 2.8 million km2 (36%) of the Australian continent. Trophic analysis reveals a bottom-up pattern of mortality concentrated in primary producer, herbivore, and omnivore guilds. Spatial and temporal reconstruction of premortality rainfall shows that mass mortality and synchronous ecosystem-wide collapse emerged in multiple geographic hotspots after 2 to 4 y of severe (>40%) and intensifying rainfall deficits. However, the presence of hyperabundant herbivores significantly increased the sensitivity of ecosystems to overgrazing-induced meltdown and permanent ecosystem change. The unprecedented taxonomic breadth and spatial scale of these impacts demonstrate that continental-scale megadroughts pose a major future threat to global biodiversity, especially in ecosystems affected by intensive agricultural use, trophic simplification, and invasive species.

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“…Data were collected in 1,327 sites in West Africa (Figure 2) during 11 years, 2007–2017. In each site, we counted all trees and birds usually along three transects (50 x 300 m each) in a triangular configuration (4.5 ha in total; Zwarts et al 2018). We followed a stratified sampling regime by selecting study sites at latitudes intersecting tracks and roads at 16.000°N, 16.050°N and so on (between-site distances of at least 5.5 km), alternately to the left and right side of the track.…”

Section: Methodsmentioning

confidence: 99%

“…Zwarts et al 2009, Vickery et al 2014), especially in the 1970s and 1980s when the rainfall in the Sahel was exceptionally low and many savanna trees died (e.g. Gonzalez 2001, Trichon et al 2018, Zwarts et al 2018). We view the decline of the migratory arboreal birds in the perspective of the decline and fragmentation of woody cover in the wintering area.…”

Section: Introductionmentioning

confidence: 99%

Arboreal birds do not avoid scattered trees in West Africa

Zwarts¹,

Bijlsma

Kamp³

2018

Bird Conservation International

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SummaryArboreal birds tend to remain in woody vegetation and avoid crossing open areas. Therefore, few tree-dwelling birds are to be expected in scattered trees. We tested this expectation with field data collected in the deserts, savannas and open agricultural parklands of West Africa where woody cover in 1,327 stratified random study sites varied between 0.2 and 29%. We found no evidence that scattered trees were avoided. Instead, bird density in trees was independent of trees occurring clumped or singly. The presence of birds in an individual tree was related to tree species and tree-related variables, but not to woody cover or species composition of the surrounding woody vegetation. We hypothesise that scattered trees are not avoided because (1) travel time between trees is too short to have a negative impact on foraging time, (2) predation risk of arboreal passerines is very low (bird-hunting raptors are scarce in the deserts and savannas of West Africa and mostly prey on ground-feeding, not arboreal, birds), and (3) the probability of being chased away by other arboreal birds is less when trees are more scattered. Scattered trees are ecologically important since hundreds of millions of migratory woodland birds, of which several species are in decline, spend the northern winter in Africa in open, often human-modified, landscapes where trees are well spaced.

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Large decline of birds in Sahelian rangelands due to loss of woody cover and soil seed bank

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Cited by 29 publications

References 22 publications

Disentangling the effects of environmental conditions on wintering and breeding grounds on age‐specific survival rates in a trans‐Saharan migratory raptor

Disentangling the effects of environmental conditions on wintering and breeding grounds on age‐specific survival rates in a trans‐Saharan migratory raptor

Historical reconstruction unveils the risk of mass mortality and ecosystem collapse during pancontinental megadrought

Arboreal birds do not avoid scattered trees in West Africa

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