Chapter 10 



Marbled Murrelet Inland Patterns of Activity: Defining 

 Detections and Behavior 



Peter W. C. Paton 1 



Abstract: This chapter summarizes terminology and methodology 

 used by Marbled Murrelet (Brachyromphus marmoratus) biolo- 

 gists when surveying inland forests. Information is included on the 

 types of behaviors used to determine if murrelets may be nesting in 

 an area, and the various types of detections used to quantify 

 murrelet use of forest stands. Problems with the methodology are 

 also discussed. 



Censusing Marbled Murrelets (Brachyramphus mar- 

 moratus) at inland forest sites presents a relatively unique 

 problem to avian ecologists attempting to assess population 

 trends, determine current population densities, or merely 

 quantify the presence or absence of birds on a specific tract 

 of land. In contrast to most avian species which tend to be 

 relatively sedentary and territorial on their breeding grounds 

 (see Ralph and Scott 1981), murrelets are considerably more 

 difficult to detect near their nests (e.g., Naslund 1993a; 

 Nelson and Hamer. this volume a; Singer and others 1991). 



Murrelets tend to be detectable at inland forested sites 

 only at dusk and dawn, and most observations are auditory 

 detections of birds vocalizing while flying overhead (e.g., 

 Naslund and O'Donnell, this volume; O'Donnell 1993; 

 Rodway and others 1993b). In addition, murrelets are non- 

 vocal near their nests (e.g., Naslund 1993a; Nelson and Hamer, 

 this volume a; Singer and others 1991), suggesting that birds 

 heard calling are often not near their own nest. Murrelets 

 have been recorded as far inland as 84 km, with downy 

 chicks found up to 64 km inland (Hamer and Nelson, this 

 volume b: Ralph and others 1994). Therefore, murrelets 

 observed flying overhead may be great distances from their 

 breeding stands. Finally, virtually nothing is known about 

 what percentage of birds visiting inland sites is non-breeding 

 birds; this can be greater than 25 percent at Ancient Murrelet 

 (Synthliboramphus antiquus) colonies (Gaston 1990). 



Detections provide a relative index to murrelet 

 abundance, and presently have not been used to calculate 

 density estimates. This is because individual murrelets will 

 often circle over the forest canopy for long periods of time, 

 vocalizing (Hamer and Cummins 1990, 1991; Naslund 1993a; 

 Nelson 1989: Rodway and others 1993b). Therefore, a series 

 of calls could represent a single bird or several birds. Unless 

 a bird is under constant observation, it is usually extremely 

 difficult to determine how many birds a series of detections 

 actually represents. 



1 Biologist, Utah Cooperative Fish and Wildlife Unit, Utah State 

 University, Logan, UT 84322 



Although biologists have attempted to quantify murrelet 

 use patterns on inland forested sites for about eight years, 

 the biological significance of these data has yet to be 

 determined. Only when an actual nest site is found can one 

 be certain that murrelets are breeding in a particular forest 

 stand. All other types of observations only suggest, with 

 varying degrees of certainty, that murrelets may be nesting 

 in a specific tract of land forest tract. There is no definitive 

 evidence that Marbled Murrelet use inland sites for night 

 roosts. Birds in some areas can be detected at inland sites 

 virtually year-round (Naslund 1993b). Only within the past 

 five years have detailed behavioral observations taken place 

 at nest sites. This information may aid in pinpointing nest 

 sites by determining if murrelets give any unique behavioral 

 clues near nests sites (e.g., Naslund 1993a). Many of those 

 data are summarized for the first time by Nelson and Hamer 

 in this volume a. 



The primary objective of this chapter is to give some 

 sense of the types of data ornithologists have collected over 

 the past eight years to quantify murrelet activity levels at 

 inland forested sites. It is hoped that these data, specifically 

 detection rates, can eventually be converted to a relative 

 index to determine the approximate number of murrelets 

 using a forest stand. Given the current state of the art 

 concerning murrelet detection rates, comparisons between 

 forest tracts are best done with data that were collected at the 

 same time of year using similar methodology (e.g., fixed- 

 point count for the entire morning survey period). Given 

 those criteria, areas that have an order of magnitude difference 

 in detection rates (e.g., 10 detections versus 100 detections) 

 probably have different numbers of birds using each area, 

 but exactly how many birds a specific detection rate represents 

 remains uncertain. 



Given this brief summary of the problems with surveying 

 murrelets at inland sites, the following summarizes the 

 methodology used by most ornithologists to quantify murrelet 

 activity levels at inland sites: 



Definition of Detection 



The primary method for censusing Marbled Murrelets 

 at inland forested stands is surveying from fixed points for 

 varying amounts of time: 10 minutes (Paton and Ralph 

 1990) to 2-3 hours (Naslund 1993a, O'Donnell 1993). The 

 sampling unit of inland surveys is a Detection, defined as the 

 sighting or hearing of one or more murrelets acting in a 

 similar manner (Paton and others 1990, Ralph and others 

 1994). Therefore, only when the observer is certain that 

 vocalizations are coming from the same bird or flock of 



USDA Forest Service Gen. Tech. Rep. PS W- 152. 1995. 



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