Burkett 



Chapter 22 



Food Habits and Prey Ecology 



Table 7 Calorific values (kj/g) and total energy content (kj) of Lesser sand eel (Ammodytes marinus) and 

 Atlantic herring (Clupea harengus) 1 



1 Data from Hislop and others (1991) 



there are numerous coastal lagoons and estuaries which may 

 be important to murrelets. 



Intensive studies on factors affecting sand lance 

 distribution and abundance are needed, as well as further 

 exploration of the food web of this species. The importance 

 of this little-studied fish in the diet of murrelets from Alaska 

 to California certainly indicates a need for further investigation 

 of predator-prey interactions. Monitoring of sand lance 

 populations may prove useful for comparisons with murrelet 

 population and productivity estimates from at-sea surveys. 

 Sand lance recruitment could potentially serve as an indicator 

 of murrelet reproductive success. A strong correlation was 

 reported between number of tern chicks available for banding 

 and recruitment of sand lance (Monaghan and others 1989). 

 The effect of pollution and physical disturbance (dredging) 

 on sand lance populations needs management attention (Auster 

 and Stewart 1986, Nakata and others 1991, Pinto and others 

 1984). Identification of sand lance spawning areas could aid 

 conservation of the murrelet through directed management 

 of these sites. 



The threatened and endangered status of the murrelet, 

 coupled with the low productivity estimates, indicates the 

 need for intensive field work in order to determine food 

 habits without sacrificing birds. Long hours of observation 

 of murrelets at sea catching and holding fish will be necessary, 

 and intensive, systematic searches for beached birds could 

 yield specimens for studies of food habits. Plankton hauls 

 along with traditional methods of assessing marine fish can 

 be used in areas where murrelets are actively foraging to at 

 least determine prey abundance and composition. Video 

 footage of prey items along with collections of fish parts 

 from nest sites can contribute to knowledge of murrelet diet. 

 Specimens can also be obtained from gill netting operations 

 and oil spill events. Stomach pumping or emetics could 

 possibly be employed, especially in conjunction with radio- 

 telemetry studies and banding or marking operations. 



The identification of important foraging areas near known 

 murrelet nesting sites will help in the conservation of this 

 species (Ainley and others, this volume). Human activities or 

 influences which are detrimental to the murrelets or their prey 

 resources could then be appropriately managed in such areas. 



Clark and others ( 1 990) compared habitat structure and 

 the number of active nests for Red-tailed Tropicbirds 

 (Phaethon rubricauda) before and after an El Nino event. 

 An increase in availability of quality habitat post-El Nino 

 resulted in an increase in the number of active nest sites 

 relative to pre-El Nino breeding seasons. The data of Clark 

 and others supported the hypothesis that suitable nest sites 

 may limit short-term reproductive opportunities of tropicbirds 

 and, hence, influence the rate of population growth and time 

 course of recovery from catastrophic events such as El Nino. 

 This has important management implications for a threatened 

 species such as the murrelet. Inland nesting habitat becomes 

 a very important management consideration even though the 

 murrelet relies on the marine environment for food. A study 

 on the Red-throated Loon (Gavia stellata) indicated that as 

 distance from the ocean to the nest site increased, both 

 density and nesting success of loons decreased (Eberl and 

 Pieman 1993). The authors suggested that the higher density 

 of breeding loons in areas near the ocean reflected a preference 

 by these birds for nesting grounds that are closer to their 

 foraging areas. 



Since the murrelet is a forest-nesting seabird, it is 

 imperative to consider multiple factors when devising research 

 and management strategies. Because of its secretive nesting 

 habits, it has been difficult to document nest success relative 

 to prey abundance as has been done with other seabirds. 

 Even if adult murrelets can easily choose alternate prey 

 species for their own diet, having abundant forage fish 

 available during the nestling period may significantly reduce 

 the energy demand on the adults by requiring less foraging 

 time and fewer trips inland for feeding nestlings (Carter 

 1984, Carter and Sealy 1990, Cody 1973, Sealy 1975c). The 

 juxtaposition of nesting areas and foraging areas is probably 

 most critical as one determinant of reproductive success in 

 years of low prey abundance. Increased foraging time of 

 adults, long flights inland, and more numerous trips inland 

 with small prey items would potentially reduce both adult 

 and chick survival. Competition with other seabirds for 

 available food is also an important factor in foraging patterns 

 and prey selection (Ainley and Boekelheide 1990: 380; Cody 

 1973; Mahon and others 1992). 



244 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



