Paton 



Chapter 10 



Defining Detections and Behavior at Inland Sites 



birds, is the observation classified as a single detection. Two 

 birds under observation simultaneously, but behaving 

 differently, are categorized as two separate detections. Hamer 

 and Cummins (1990) required a minimum time interval 

 between call notes to classify an observation as two detections. 

 The total number of birds in a detection represents the total 

 group size. Therefore, biologists can quantify detection rates 

 between study sites (e.g., Naslund 1993b), and also determine 

 annual fluctuations in mean total group size at the same site 

 (e.g., Rodway and others 1993b). 



Rodway and others (1993) also suggested an alternative 

 method to quantify murrelet activity patterns would be to 

 count all vocalizations and visual detections, rather than 

 keep track of total detections. 



Type of Detection 



Murrelet detections are generally classified into one 

 of three categories: (1) the bird was only heard and not 

 seen (i.e., an audio detection); (2) the bird was seen and 

 not heard (a visual detection); or (3) the bird was both seen 

 and heard (see Ralph and others 1994). Audio detections 

 are usually subdivided into separate types of vocalizations 

 and mechanical sounds, in the hope that future researchers 

 will be able to determine the context when a specific 

 vocalization is given. As far as I know, there is no unique 

 vocalization given only at the nest that would aid researchers 

 in finding nests (Nelson and Hamer, this volume a). Listed 

 below are the current categories for types of vocalizations 

 and visual detections. 



Types of Audio Detections 



(1) Keer calls two-syllable, high-pitched vocalization, 

 similar to the vocalizations of many gulls (Larus spp.) 

 (O'Donnell 1993). When properly trained, there appears to 

 be little observer bias in quantifying the number of keer calls 

 given by murrelets (Rodway and others 1993b). During the 

 summer months in northern California, 91.1 percent of the 

 detected birds vocalized, compared to 98.7 percent during 

 the winter months (O'Donnell 1993). In addition, O'Donnell 

 (1993) found in the summer that murrelets flying above the 

 canopy were significantly more likely (P < .001) to vocalize 

 than birds flying below the canopy. Rodway and others (1993) 

 found the number of detections increased on cloudy days, but 

 the number of calls per detection was not affected by weather. 



(2) Non-keer calls A low, two-part, guttural vocal- 

 ization, which some researchers believe is associated with 

 reproductive behavior. However, O'Donnell (1993) heard 

 murrelets give non-keer vocalizations all months of the year, 

 although at a reduced rate from December through February. 

 In addition, O'Donnell (1993) found in his study of nine 

 forest stands, that an average of 12 percent of murrelet 

 detections had one or more non-keer vocalization (range = 

 7.5-2 1 .9 percent). For further details, see Nelson and Hamer 

 (this volume a) who have subdivided non-keer vocalizations 

 into whistle- and groan-like calls. 



(3) Stationary calls Detections with three or more calls 

 that are 100 m or less from the observer, where the observer 

 believes the bird has not moved, are classified as a Stationary 

 Detection (Ralph and others 1994). 



(4) Wing beats A tremulous, fluttering sound presumably 

 generated by movement of a murrelet' s wings through the air. 

 Singer and others (1991) heard wing beats near active nest 

 sites, and wing beats were also heard every morning near an 

 active nest in northern California (Forma, pers. comm.). Wing 

 beats were heard on 0.5 percent of detections at nine sites 

 in northwestern California (O'Donnell, pers. comm.). 



(5) Jet dive Little is known about the origin or function 

 of the jet dive, or power dive, which makes a sound somewhat 

 similar to the roar of a jet engine. It is heard rarely, comprising 

 only 10 of 21,437 detections at nine sites in northwestern 

 California (O'Donnell, pers. comm.). This sound is 

 presumably a mechanical sound made by murrelet' s feathers 

 while in a steep dive above the forest canopy. Nelson and 

 Hamer (this volume a) report in Oregon on the rare occasions 

 when this sound is heard, it is usually near a nest tree. 



Visual Detections 



Rodway and others (1993) found significant variation 

 between observers in the proportion of murrelets that were 

 visually detected. This suggests that biologists doing field 

 work should be screened and trained to insure that there is 

 minimal observer bias (see also Ralph and others 1994 for 

 training details). Categories for visual detections include: 



(1) Birds flying above the canopy This includes both 

 straight-line flight and circling over a forest stand. This was 

 the most frequently observed type of detection in a study of 

 nine study areas in northwestern California, ranging from 8 

 to 33 percent of all detections (O'Donnell 1993). In British 

 Columbia, 75-89 percent of all detections were birds flying 

 over the canopy (Rodway and others 1993b). 



(2) Birds flying below the canopy This refers to 

 murrelets both flying through a forest stand and adjacent to 

 the stand. O'Donnell (1993) found that at Lost Man Creek in 

 northern California, 25 percent of murrelet detections during 

 the summer months (April-August) were birds flying below 

 the canopy, compared to 0.4 percent during the winter months 

 (September-March). Rodway and others (1993b) found that 

 more birds flew below the forest canopy in June than during 

 other times of the year. 



(3) Landing and perching in a tree O'Donnell (1993) 

 found 0.4 percent of the total summer detections (April- 

 August) at Lost Man Creek were of birds landing in trees (n 

 = 10,154), although no nests were found in this area. At two 

 active nests, Naslund (1993a) observed birds flying to the 

 nest for incubation exchanges 3 1 minutes before sunrise to 3 

 minutes after sunrise (see also Nelson and Hamer, this volume 

 a). Adults typically took predictable flight paths to the nest 

 (Nelson and Hamer, this volume a). Murrelets incubate for 

 24-hour bouts (Naslund 1993a, Nelson and Hamer, this volume 

 a, Singer and others 1991). Nest exchanges and feedings 

 generally took place 17-24 minutes before sunrise, with two 



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



