Hamer and Nelson 



Chapter 6 



Characteristics of Nest Trees and Nesting Stands 



slopes that are commonly used by other alcids as nesting 

 habitat, are not commonly available along the forested coasts 

 of the Pacific Northwest. Old-growth and mature forests 

 also provided large nesting platforms on which to raise 

 young. Nesting greater distances from the coast may have 

 developed over time to avoid higher nest predation by corvids 

 and gulls whose population numbers may be much higher in 

 food-rich coastal areas. In addition, much of the near-coastal 

 nesting habitat has been eliminated in the Pacific Northwest 

 which may cause birds to nest further inland. Nest search 

 efforts and surveys for the presence of murrelets should be 

 conducted in areas farther inland in order to refine the 

 abundance and distribution of this seabird away from the 

 coast. We currently have no information to determine what 

 proportion of the population nests in these inland areas, or 

 any data to compare the reproductive success of far versus 

 near-coastal nesting pairs. 



In Washington, inland detection rates of Marbled 

 Murrelets did not show declines until inland distances 

 were >63 km from salt water (Hamer, this volume). In 

 Oregon, most detections occurred within 40 km of the 

 ocean (Nelson, pers. obs.). In British Columbia, murrelet 

 detection rates in Carmanah Creek on Vancouver Island 

 decreased with increasing distance from the ocean (Manley 

 and others 1992). Savard and Lemon (1992) found a 

 significant negative correlation between detection frequency 

 and distance to saltwater on Vancouver Island in only 1 of 

 3 months tested during the breeding season. Inland distances 

 for all nests in Alaska were low because rock and icefields 

 dominate the landscape a few kilometers from the coast in 

 most regions. 



We found that all nest trees throughout the geographic 

 range were located in stands defined by the observers as old- 

 growth and mature stands or stands with old-growth 

 characteristics. The youngest age reported for a nesting stand 

 was 180 years. Marbled Murrelet occupancy of stands, and 

 the overall abundance of the species has been related to the 

 proportion of old-growth forest available from studies 

 conducted in California, Washington, and Alaska (Hamer, 

 this volume; Kuletz, in press; Miller and Ralph, this volume; 

 Raphael and others, this volume). Carter and Erickson ( 1 988) 

 reported that all records of grounded downy young and 

 fledglings (young that have fallen from a nest or unsuccessfully 

 fledged) (n = 17) that they compiled were associated with 

 stands of old-growth forests in California. All records of 

 nests, eggs, eggshell fragments, and downy chicks in 

 Washington have been associated with old-growth forests (n 

 = 17) (Hamer, this volume; Leschner and Cummins 1992a). 



Marbled Murrelets consistently nested in low elevation 

 (<945 m) old-growth and mature forests. Tree species that 

 are most abundant at lower elevations (<945 m) such as 

 Douglas-fir, western hemlock, Sitka spruce, redwood, and 

 cedar, may have a higher abundance of potential nest platforms 

 than the higher elevation conifers such as silver fir and 

 mountain hemlock. 



Marbled Murrelets were found nesting in stands of very 

 small size in some instances, although the reproductive success 

 of these nests compared to stands of larger sizes was not 

 known (but see Nelson and Hamer, this volume b). A wide 

 range of canopy closures were reported for nest stands and 

 around nest sites. A study conducted in Washington and 

 Oregon compared random plots within a stand to plots 

 surrounding the nest tree (Nelson and others, in press). They 

 found that canopy closures were significantly lower around 

 nest trees in Oregon compared to random plots adjacent to 

 the nest tree, but the relationship was not significant in 

 Washington. It is unknown how stand size and canopy closure 

 affect nest success, but stands with lower canopy closures 

 might have less visual screening to conceal adult visits to the 

 nest tree (see Nelson and Hamer, this volume b). Therefore, 

 it is possible that low canopy closures within a stand will 

 make locating nests easier for visual predators such as corvids. 

 In addition, smaller stands will have fewer nesting and hiding 

 opportunities for Marbled Murrelets. They may be choosing 

 lower canopy closures immediately around the nest to improve 

 flight access, but select nest platforms with dense overhead 

 cover for protection from predation, as indicated by the 

 extremely high cover values found directly over the nest. 



The majority of nests in the Pacific Northwest were 

 located within 100 m of water, but a few nest sites were 

 found at much longer distances (fig. 3). Small streams and 

 creeks commonly bisect stands in the Pacific Northwest, 

 creating larger openings and long travel corridors. Murrelets 

 are often observed using these features to travel through a 

 stand. This may be one reason nest sites were often in close 

 proximity to streams. Many nests were also located near 

 openings such as roads or clear-cuts, but there may be an 

 observer bias to finding nests located in areas with better 

 access and viewing conditions. 



A variety of processes contributed to producing potential 

 nest platforms within the forest including deformations and 

 damage sustained by trees. This is probably why a measure 

 of potential nest platforms, and not tree size, was the best 

 predictor of stand occupancy by murrelets in Washington 

 (Hamer, this volume), as larger diameter trees alone were 

 often not responsible for the majority of available platforms 

 within a stand. Mistletoe blooms, unusual limb deformations, 

 decadence, and tree damage commonly observed in nest 

 stands, all appear to create a large number of nest platforms. 

 Therefore, the structure of a stand and the processes occurring 

 within a stand may be more important than tree size alone in 

 producing nesting platforms and suitable habitat for the 

 Marbled Murrelet (see Grenier and Nelson, this volume). 



It would still be desirable to know when trees, in general, 

 begin producing potential nest platforms. In Washington, 

 Hamer (this volume) measured potential nest platform 

 abundance using a sample of 2,035 conifers, and found 

 platforms were generally available when tree diameters 

 exceeded 76 cm. The mean number of platforms/tree was 

 found to increase rapidly with an increase in tree diameter 



80 



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



