Table 2.
Overview of samples and methods of analysis combined for noninvasively obtained dietary samples of piscivorous birds including sampling and analysis effort and information content per combination. Information is based on Duffy and Jackson (1986), Carss and Group (1997), Barrett et al. (2007), and the results obtained within the presented study
| Pellets | Feces | Fish samples | ||||
|---|---|---|---|---|---|---|
| DNA‐based | Morphological | DNA‐based | Morphological | DNA‐based | Morphological | |
| Sampling effort | Easily visible; collectable from soil; individual, DNA‐free sampling necessary for molecular analysis | Hardly collectable from soil; artificial surface, e.g., cellulose fleeces advisable; low urea content preferable; individual, DNA‐free sampling necessary for molecular analysis | Whole regurgitated fish easily visible and collectable; small fish parts, e.g., muscle tissue difficult to collect; individual, DNA‐free sampling necessary for molecular analysis | |||
| Analysis effort | Lysis, DNA extraction, PCR and visualization | Washing, sieving, sorting, identification | Lysis, DNA extraction, PCR and visualization | Washing, sieving, identification | Lysis, DNA extraction, PCR and visualization | Washing, sieving, identification |
| Prey consumption time frame | One day; earlier ingested prey less likely detected | One day; more if hard parts are not completely regurgitated | Subsample of one meal | Subsample of one meal | One consumption plus fish DNA in the stomach at point of regurgitation | One consumption |
| Identification level | Species | Depending on fish family and digestive damage to hard parts; often only order level | Species | Hardly any hard parts; only distinct hard parts identifiable | Species | Species (whole fish); depending on sample: order, family, and species ID sometimes possible from fish parts |
| Individual count | – | Possible but not necessarily accurate | – | – | – | – |
| Distinct features | Best suitable for detection of complete prey spectrum. | Estimation of consumed fish individuals possible; time‐consuming | Uric acid can hamper DNA‐based analysis | Strong influence of digestion upon few detected hard parts | Species identification not always possible due to contamination in stomach | Whole fish can be further used for estimation of secondary predation |