De Santo and Nelson 



Chapter 3 



Reproductive Ecology of Auks 



where they receive additional care for several weeks until 

 independent (table 8). 



Marbled Murrelet chicks are semi-precocial and remain 

 in the nest where they are cared for by both parents until 

 fledging at 27 to 40 days of age (tables 7 and 8). The chick is 

 apparently able to thermoregulate at an early age as continuous 

 brooding by the parents ceases after 1-3 days (Naslund 

 1993a; Nelson and Hamer, this volume a; Nelson and Peck, 

 in press; Simons 1980; S.W. Singer, pers. comm.). The 

 period of continuous brooding is shorter than most alcids 

 raised in the nest (semi-precocial and intermediate species) 

 and is comparable to that of the precocial murrelets (table 

 7). Growth data have been collected for only four nestlings, 

 the preliminary data suggest murrelets grow more rapidly 

 than comparable alcids (Hamer and Cummins 1991; Hirsch 

 and others 1981; Simons 1980). 



The incubation and nestling periods of semi-precocial 

 alcids are related (fig. 6, r 2 = 0.68, P < 0.001), however, the 

 precocial and intermediate species do not fit this pattern. (The 

 relationship between the incubation and the nestling period 

 including the alcids with precocial and intermediate 

 developmental modes is not significant [r 2 = 0.19, P < 0.07]). 



Lengthy incubation and nestling periods have been 

 attributed to slow rates of development (Manuwal 1979). In 

 contrast, Marbled Murrelets appear to have a relatively short 

 incubation and nestling period indicating a rapid rate of 

 development. However, the nestling stage of the Marbled 

 Murrelet can vary between 27 and 40 days and the extended 

 growth period may reflect parental difficulty in provisioning 

 the nestling (Nelson and Hamer, this volume a; Nelson and 

 Hardin 1993a). Barrett and Rikardsen ( 1992) reported lengthy 

 nestling periods of Atlantic Puffins during years of food 

 shortages when parents delivered less food to their young. 



Estimates of mean fledging success range from 66 percent 

 for Crested Auklets to over 90 percent for the Ancient 

 Murrelets and Wiskered Auklet (table 6). Causes of pre- 

 fledgling mortality include mammalian, avian, and reptilian 

 predation (Emms and Verbeek 1989; Evans 1981; Ewins 

 and others 1993; Gaston 1994; Jones 1992; Manuwal 1979; 

 Sealy 1982; Thorensen 1964), food shortages or starvation 

 (Ainley and Boekelheide 1990; Barrett and Rikardsen 1992; 

 Manuwal 1979; Vermeer 1980), adverse weather (reviewed 

 by Harris and Birkhead 1985), and injury inflicted by adult 

 conspecifics (Birkhead and Nettleship 1981). 



Fledging success of Marbled Murrelets has been estimated 

 to be 45 percent, a value lower than those of other species 

 (table 6). Chicks in 19 nests were monitored in Alaska, 

 California, Oregon, Washington, and British Columbia (Nelson 

 and Hamer, this volume b). Nearly 25 percent of these young 

 were documented or strongly suspected to have been taken 

 by predators, three others fell from their nest trees, and one 

 died of unknown causes. 



Although juvenile survival is difficult to observe and 

 measure, banding studies have provided estimates of survival 

 for seven alcid species ranging from below 1 percent for 

 Atlantic Puffins to a high of 65 percent for Cassin's Auklets 



>. 

 

 o 



a 

 o 



w 



a> 



a. 



o> 



c 



en 



a> 



z 



60- 



40 H 



20 - 



r 2.47 + 1.02x 

 *2 = 0.68 



y = - 8.78 + 1.15X 

 R A 2 r 0.19 



1 



i 

 3 



5 



7 



Incubation period (days) 



Figure 6 Relationship between incubation and nestling periods for 1 9 

 alcids (see tables 5 and 9 for values). 



(table 6). Juvenile survival has not been estimated for Marbled 

 Murrelets. It is likely that recently fledged Marbled Murrelets 

 experience some mortality on their trip from inland nest trees 

 to the ocean. Forty-six juveniles in postfledging plumage 

 have been found on the forest floor or in parking lots, 

 presumably following unsuccessful attempts at fledging from 

 inland nests (see Nelson and Hamer, this volume b). An 

 indication of low fledgling success is also reflected in at-sea 

 surveys conducted in California, Oregon, and Alaska in which 

 only 1 to 5 percent of birds on the water were observed to be 

 recently fledged young (Nelson and Hardin 1993a; Ralph 

 and Long, this volume; Strong and others, in press; Strong 

 and others, this volume; Varoujean and Williams, this volume). 



Although the average number of young produced by 

 alcid pairs can be high in some years, it is common for 

 productivity to be variable among years, and extremely 

 low reproductive rates are not uncommon. For example, 

 over a 12-yr period on the South Farallon Islands, Common 

 Murre pairs produced an average of 0.86 young per season, 

 but values over this time fluctuated from a high of 0.9 to a 

 low of 0.1 fledglings (Boekelheide and others 1990). 

 Complete nesting failures have been documented as well 

 (Bergman 1971). 



Summarizing the available information on the repro- 

 duction of Marbled Murrelets, it appears that this alcid has a 

 low reproductive rate. This species lays only one egg, has 

 relatively low hatching success and fledgling survival, and a 

 low rate of recruitment of young into the population. However, 

 some of the Marbled Murrelet reproductive data were collected 

 during El Nino periods (Ainley 1990). Because reproduction 

 of other alcids has been documented to be low during such 

 times (Boekelheide and others 1990), values reported for 

 Marbled Murrelets may reflect a similar depression. 

 Reproduction in "good" years may be higher. On the other 



46 



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



