Ralph and others 



Chapter 1 



Overview of Ecology and Conservation 



declined on the order of 50 percent in the last 10 to 20 years. 

 Piatt and Naslund (this volume) based their conclusions on a 

 decrease in the number of birds seen on small boat surveys of 

 Prince William Sound in 1972-1973 compared to 1989-1991, 

 as well as declines from Christmas Bird Counts during this 

 period. Burger (this volume b) based his conclusions for 

 Clayoquot Sound on density estimates from surveys made 

 between 1979 and 1993. In Barkley Sound, British Columbia, 

 Burger (this volume b) also found evidence of a decline from 

 work in 1992 and 1993. However, in this area in the spring of 

 1994, he recorded 2-3 times as many murrelets, leading to the 

 possibility that the low numbers in 1992 and 1993 were due 

 to El Nino-like effects in those years. 



The murrelet populations in Puget Sound, Washington, 

 are apparently now lower than earlier this century. Few 

 counts of offshore populations have been performed in the 

 state, but Speich and Wahl (this volume) indicate some 

 declines in recent decades. Both they, as well as Piatt and 

 Naslund (this volume) in Alaska, suggest that some proportion 

 of these declines may be linked to large-scale factors 

 influencing the prey of marine bird populations over the past 

 few decades, or that short-term environmental phenomena, 

 such as El Nino events, may have caused local population 

 declines or redistribution. They also identify a number of 

 other factors that may have contributed to murrelet declines, 

 including oil spills, gill netting, and timber harvest. 



Although quantitative evidence concerning population 

 trends is not available for Oregon and California, it is our 

 judgment that the long-term trends have been downward in 

 these states, as well as in Washington. Murrelets require 

 forests with old-growth characteristics for nesting, and with 

 the loss of their nesting habitat and incidental take in fishing 

 nets and oil spills, Marbled Murrelet populations in the three 

 states are almost certain to have decreased, as they have in 

 Alaska and British Columbia. The declines in these latter 

 two regions appear to have coincided with the cutting of a 

 large fraction of the old-growth forests. The cumulative 

 effects of oil pollution, gill netting, and natural changes in 

 the marine environment have undoubtedly played a role as 

 well. We are not able to separate these potential causes of 

 decline at this point, but the declines, whatever their origin, 

 are at least a cause for concern. 



Beissinger (this volume) has estimated an annual 

 decline of at least 4-6 percent throughout the species' 

 range. These estimates are largely based on the observation 

 of adult-to-young ratios at sea in the late summer, and 

 inferences from other alcid species. However, the age 

 ratio data are controversial, are from years when ocean 

 conditions were warmer than usual, and may reflect a 

 relatively temporary decline in reproduction. In addition, 

 inferences from other species are fraught with danger. 

 These estimates apply to past conditions and cannot be 

 projected into the future, especially since implementation 

 of the U.S. Government's Forest Plan would conserve 

 most remaining nesting habitat on Federal lands of 

 California, Oregon, and Washington. 



Demography of the Marbled Murrelet 



Summary Based on the rate of successful fledging of 

 young from observed nests, Marbled Murrelet populations 

 in recent years have had one of the lowest reproductive rates 

 of any alcid population thus far studied. For the population 

 to be stable, these low rates of reproduction must be increased 

 or balanced by higher than average rates of adult survival. 

 Factors affecting these demographic parameters are the 

 possible exclusion of a portion of the adult population from 

 breeding due to lack of suitable nest sites, a decrease in the 

 number of breeding attempts due to food limitation, loss of 

 nest contents to avion predators, and mortality of adults 

 from both avion predators and human activities, especially 

 oil spills and entanglement in nearshore gill nets. 



Long-term demographic data on adult survival, chick 

 production, and chick survival, would be useful for 

 determining whether murrelet populations are decreasing, 

 stable, or increasing. These data would also help in 

 evaluating the significance of threats to different components 

 of the population, such as reduced productivity, and chick 

 and adult mortality. For example, a 50 percent increase in 

 juvenile predation might not be as serious as a 10 percent 

 increase in adult mortality from gill-net losses, depending 

 on what would be considered the normal range of these 

 population parameters. Some species of alcids, such as 

 Common Murres (Uria aalge), can recover from relatively 

 large population losses because they have, for alcids, 

 typically high levels of annual production, with 0.5-0.9 

 chicks fledging per pair (Hudson 1985). For species with 

 low rates of reproduction, high rates of adult survival are 

 essential for a stable population. 



It is exceptionally difficult to measure most of the critical 

 population parameters for Marbled Murrelets. The traditional 

 method of banding and resighting large numbers of seabirds 

 at their colonies to estimate annual adult survival cannot be 

 employed for murrelets because they are inaccessible. For 

 example, a study of Common Murre breeding success at a 

 single site in one year might include observations on hundreds 

 of breeding pairs, and involve the banding of hundreds of 

 chicks. At the end of the 1993 breeding season, after many 

 years of dedicated effort, we have breeding success 

 information on only 32 murrelet nests (Nelson and Hamer, 

 this volume b). We do not know how representative these 

 data are for the population as a whole. The only other source 

 of demographic information is the ratio of juveniles to adults 

 observed at sea during the post-breeding period (Ralph and 

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

 These are based on the identification of juveniles and adults 

 on the water. As Carter and Stein (this volume) describe, this 

 separation is fraught with difficulty. The extrapolation of 

 these demographic data to longer time periods may be of 

 limited value because many of the available data on 

 juvenileiadult ratios were obtained in years when sea surface 

 temperatures were unusually warm and prey availability 



12 



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



