Yesterday, I was wondering after seeing several videos of them disappearing from view, just how deep these seabirds dive for pray when they have to. I found the following source
here:
DETAILED INFORMATION
General feeding behaviour
Black Guillemots are mostly bottom feeders, searching bottom vegetation for fish, but may also take prey in transit between bottom and surface [9, 10, 11, 13, 14]. They propel themselves through the water using primarily their wings.
Foraging habitat breeding season, migration and wintering period
Black Guillemots feed mainly in shallow inshore waters during the breeding season, especially within the littoral-sublittoral boundary, but more offshore in winter [15]. They are considered the most inshore of alcids and are rarely found far offshore [27]. Black Guillemots in the Bay of Fundy, Canada, generally preferred waters of moderate current velocity (3068 cm/s) and intermediate depth (1731 m) [26], which appears to be related to minimizing energy expenditure. They also appeared to use passive drift with ebbing tides and short-distance flights to reposition in optimum feeding zones.
The species tends to forage over hard-bottomed areas or ledges [26, 32]. In Shetland, U.K., Black Guillemots tend to forage where the seabed is rocky and vegetated with dense stands of Laminaria kelp [18], reflecting the habitat preferences of their main prey - butterfish
Pholis gunnellus and blennies (Blenniidae); in the Bay of Fundy, birds preferred islands with extensive underwater ledges, presumably because these harboured sufficient prey and provided protection from fast-moving tidal waters [26].
In areas where coastal waters freeze, birds move into offshore pack ice [7], and birds often forage along ice edges over pelagic waters and feed on less diverse fauna under sea ice [5, 23]. For instance, the observed distribution of Black Guillemots in March, April, and May in Jones Sound, North West Territories, Canada, coincides with the location of open water and associated ice edges but after the ice margin recedes and shorelines open, the distribution of Black Guillemots tends to reflect the location of breeding colonies [31]. Switching of foraging strategies allows successful overwintering in high-arctic latitudes.
