Strand-Feeding Dolphins


Foraging interactions between wading birds and

strand-feeding bottlenose dolphins (Tursiops truncatus)

in a coastal salt marsh

A Fox | R Young

This research was conducted under NMFS General Authorization permit 976-1816,

and under USGS bird banding permit 22990 D.

Strand-feeding is a unique foraging technique used by Atlantic bottlenose dolphins (Tursiops truncatus Montagu, 1821) in salt marshes of the southeastern USA wherein a group of dolphins rushes a creek bank, temporarily stranding themselves to capture fish that have been pushed ashore by their bow wave. Wading birds are attracted to these events to forage on stranded fish. We hypothesized that birds foraging in association with dolphins experience greater foraging efficiency than birds foraging away from dolphins and that some birds are able to meet their entire daily metabolic needs by foraging at strand-feeding events. The species composition, abundance, and foraging success of birds at 569 strand-feeding events were compared to the same parameters from marsh surveys of birds not associated with dolphins. Only great egrets (Ardea alba L., 1758) were proportionately more common at strand-feeding events than in the marsh overall (p<0.001). During peak strand-feeding hours, energy intake per hour was higher for great egrets foraging with strand-feeding dolphins than for birds foraging away from dolphins (p=0.04). Bioenergetic models indicated that prey intake by great egrets at strand-feeding events was sufficient to meet their existence and likely their active metabolic requirements.

A new method to dye-mark wild birds

A Fox | C Hill | R Young

This research was conducted under NMFS General Authorization permit 976-1816,

and under USGS bird banding permit 22990 D.

Dye-marking of Great Egrets (Ardea alba) and Great Blue Herons (Ardea herodias) was conducted in an intertidal salt marsh in South Carolina, USA, as part of a study on wader energetics and bird/dolphin interactions. We used remotely-triggered Spraymore paintball land mines to apply dye. These compressed gas-powered mines were portable, re-useable, and capable of spraying any liquid. Using an inkjet printer ink-based dye, we were able to successfully mark and re-identify one Great Blue Heron and one Great Egret. No apparent long-term behavioral changes were observed in marked birds, which were re-sighted in the same areas and engaged in normal behaviors following the application of dye. Dye markings lasted as long as 44 days. The use of Spraymore paint mines is a viable option for marking any birds that regularly return to specific observable areas, particularly when birds in these areas are not easily marked or captured using traditional methods.