| Abstract: | A major decline in submerged aquatic vegetation (SAV) in Chesapeake Bay has altered the diet of wintering Canvasbacks (Aythya valisineria) from historically plant to a combination of benthic animal foods, especially the ubiquitous Baltic clam (Macoma balthica), supplemented with anthropogenic corn (Zea mays). Because the isotopic signature of corn is readily discriminated from bay benthos, but not SAV, we used stable-isotope methodology to investigate the corn-SAV component of the winter diet of Canvasbacks. Feeding trials with penned Canvasbacks were conducted to establish turnover rates and fractionation end-point loci of *13C and *15N signatures of whole blood for individual ducks fed ad libitum diets of (1) Baltic clams, (2) Baltic clams and corn, and (3) tubers of wild celery (Vallisneria americana). Turnover time constants averaged 4.5 weeks, indicating that signatures of wild ducks would be representative of bay diets by late February. Isotopic signatures of wild Canvasbacks sampled in February fell on a continuum between end-point loci for the Baltic clam and the combination Baltic clam and corn diet. Although that finding verifies a clear dependence on corn-SAV for wintering Canvasbacks, it also reveals that not enough corn-SAV is available to establish ad libitum consumption for the 15,000+ Canvasbacks wintering in the upper bay. On the basis of mean *13C signature of bay Canvasbacks (n=59) and ingestion rates from feeding trials, we estimated that 258 kg corn per day would account for the observed *13C enrichment and supply 18% of daily energetic needs for 15,000 Canvasbacks. That level of corn availability is so realistic that we conclude that SAV is likely of little dietary importance to Canvasbacks in that portion of the bay. |
| Genre: | Article |
| ProdID: | 5224096 |
| Citation Author: | Haramis, G.M.; Jorde, D.G.; Macko, S.A.; Walker, J.L. |
| Citation Contributing Office: | Patuxent Wildlife Research Center |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | |
| Citation Editor: | |
| Citation End Page: | 1017 |
| Citation Issue: | 4 |
| Citation Keywords: | |
| Citation Language: | English |
| Citation Larger Work Title: | Auk |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 10 |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | 1008-1017 |
| Citation Projection: | |
| Citation Public Comments: | 5772_Haramis.pdf |
| Citation Publisher: | |
| Citation Series: | |
| Citation Series Code: | |
| Citation Series Number: | |
| Citation Search Results Text: | Stable-isotope analysis of canvasback winter diet in upper Chesapeake Bay; 2001; Article; Journal; Auk; Haramis, G.M.; Jorde, D.G.; Macko, S.A.; Walker, J.L. |
| Citation Start Page: | 1008 |
| Citation Volume: | 118 |
| Citation Year: | 2001 |
| Type: | citation/reference |
| Text: | Stable-isotope analysis of canvasback winter diet in upper Chesapeake Bay; 2001; Article; Journal; Auk; Haramis, G.M.; Jorde, D.G.; Macko, S.A.; Walker, J.L. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DOCUMENT): | http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1642%2F0004-8038%282001%29118%5B1008%3ASIAOCW%5D2.0.CO%3B2 |
| Date Other: | Wed, 16 Jun 2010 12:18 -0500 |
| Publisher: | |
