Foraging guild membership explains variation in waterbird responses to the hydrological regime of an arid-region flood-pulse river in Namibia

Cumming, Graeme S., Paxton, Mark, King, Jackie, and Beuster, Hans (2012) Foraging guild membership explains variation in waterbird responses to the hydrological regime of an arid-region flood-pulse river in Namibia. Freshwater Biology, 57 (6). pp. 1202-1213.

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1. Little is known about hydrological influences on tropical waterbird communities. We used a 16-year data set (1991–2007) of waterbird censuses, together with a classification of observed species into foraging guilds, to explore the relationships between natural variations in flow regime, foraging guild and the community composition of waterbirds at the Okavango River in the Caprivi Strip of north-eastern Namibia, southern Africa.

2. We addressed three hypotheses to explain variation in waterbird community composition: (i) exploitation (birds move towards resource-rich patches to exploit periods of high food abundance); (ii) escapism (declines in regional habitat quality force birds to aggregate in perennial waterbodies); and (iii) interaction (bird assemblages are dominated by intra- and interspecific interactions, such as flock formation for breeding or moulting, that can be explained better by life history demands or competition than by resource availability).

3. Waterbirds in different foraging guilds responded strongly but at different periods to changes in the hydrological environment, creating a complex but predictable successional pattern in community composition through time. Deep-water feeders responded fastest (abundance peaking 2 months post-flood), followed by shallow-water feeders (4 months) and emergent vegetation feeders (7 months). Species that forage on short vegetation or in mud showed a bimodal response with peaks in abundance at 3 and 8 months post-flood.

4. Our results indicated a strong effect of the local flow regime and hence supported the exploitation hypothesis. The foraging guild approach allowed us to identify clear patterns in a highly complex ecosystem and shows considerable promise as an analytical tool for similar data sets. Our results further suggest that while the entire bird community will be affected by hydrological alterations such as impoundments, water extraction and climate change, deep-water feeders may be one of the most vulnerable groups.

Item ID: 40965
Item Type: Article (Research - C1)
ISSN: 1365-2427
Keywords: dispersal, flow regime, functional group, hydrology, Okavango
Funders: DST/NRF Centre of Excellence at the Percy FitzPatrick Institute
Date Deposited: 30 Nov 2015 01:31
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 50%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050199 Ecological Applications not elsewhere classified @ 50%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960501 Ecosystem Assessment and Management at Regional or Larger Scales @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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