Martin G. Raphael

Breeding Bird Populations during Twenty-Five Years of Postfire Succession in the Sierra Nevada

We summarized breeding bird censuses done from 1966 to 1985 on two Sierra Nevada forest plots, one that was burned in 1960 and an adjacent, unburned control. Our objective was to examine yearly trends in bird abundance in relation to changing vegetation structure and composition and in relation to yearly weather variation. From 1969 to 1983 shrub cover on the burned plot increased from about 22% to over 43%, and density of overstory trees increased by about 50%. Herb and grass cover decreased during this period, as did density of snags originally resulting from the fire. During this period of rapid postfire succession, total density of birds was nearly equal on the two plots but species richness increased on the burned plot compared with the unburned plot. Groundand brush-foraging birds were more numerous on the burned plot, and their population size increased significantly from 1966 to 1985. Foliage-searching birds were more numerous on the unburned plot, and their populations were stable over time relative to the burned plot. In contrast, numbers of foliage-searching birds increased significantly on the burned plot. Bark-gleaning birds declined on the burned plot, probably in response to loss of snags used for nesting by most of these species. Variations in weather, as indicated by measures of temperature and precipitation, did not explain yearly variations in bird populations. Rather, changing vegetation structure resulted in predictable trends related to the foraging and nesting habits of the birds we studied.

Limiting factors and landscape connectivity: the American marten in the Rocky Mountains

In mobile animals, movement behavior can maximize fitness by optimizing access to critical resources and minimizing risk of predation. We sought to evaluate several hypotheses regarding the effects of landscape structure on American marten foraging path selection in a landscape experiencing forest perforation by patchcut logging. We hypothesized that in the uncut pre-treatment landscape marten would choose foraging paths to maximize access to cover types that support the highest density of prey. In contrast, in the post-treatment landscapes we hypothesized marten would choose paths primarily to avoid crossing openings, and that this would limit their ability to optimally select paths to maximize foraging success. Our limiting factor analysis shows that different resistant models may be supported under changing landscape conditions due to threshold effects, even when a species’ response to landscape variables is constant. Our results support previous work showing forest harvest strongly affects marten movement behavior. The most important result of our study, however, is that the influence of these features changes dramatically depending on the degree to which timber harvest limits available movement paths. Marten choose foraging paths in uncut landscapes to maximize time spent in cover types providing the highest density of prey species. In contrast, following landscape perforation by patchcuts, marten strongly select paths to avoid crossing unforested areas. This strong response to patch cutting reduces their ability to optimize foraging paths to vegetation type. Marten likely avoid non-forested areas in fragmented landscapes to reduce risk of predation and to benefit thermoregulation in winter, but in doing so they may suffer a secondary cost of decreased foraging efficiency.

LANDSCAPE-SCALE RELATIONSHIPS BETWEEN ABUNDANCE OF MARBLED MURRELETS AND DISTRIBUTION OF NESTING HABITAT

Abstract We used radar to count numbers of Marbled Murrelets (Brachyramphus marmoratus) flying inland within 10 river drainages on the Olympic Peninsula, Washington, during 1998–2000. We tested whether the numbers of murrelets entering drainages could be predicted from the amount and spatial configuration of low-elevation, late-seral forest (potential murrelet nesting habitat) within drainages. The maximal number of murrelet radar targets was positively correlated with the amount of late-seral forest in each of the three years sampled; this relationship persisted in 1999 and 2000 when controlling for drainage size. Murrelet radar counts were not correlated with the combined amounts of harvested, developed, and agricultural lands in any year. Numbers of murrelets increased as the amount of core area of late-seral forest and proximity of patches increased, and decreased with increasing amounts of edge of late-seral patches. Numbers were not correlated with the percent of late-seral forest, patch density, patch size, road density, or the overall diversity of all habitat types within landscapes. Neither the maximal nor the mean number of inbound Marbled Murrelets differed among years; the effect of year was small relative to the effect of habitat on murrelet numbers. Our results suggest that changes in the amount or distribution of nesting habitat should result in detectable changes in murrelet numbers at the scale of individual drainages. Thus, the amount and distribution of nesting habitat may play a role in the regulation of Marbled Murrelet populations, supporting the contention that providing nesting habitat is an effective conservation and restoration technique for this species. Relaciones a Escala del Paisaje entre la Abundancia de Brachyramphus marmoratus y la Distribución de Hábitat de Nidificación Resumen.u2003Durante 1998–2000 utilizamos radares para contar el número de individuos de Brachyramphus marmoratus que volaron tierra adentro a lo largo de 10 cuencas de ríos que desaguan en la Península Olímpica, Washington, USA. Evaluamos si el número de individuos de B. marmoratus que entran por las cuencas puede ser predicho por la cantidad y configuración espacial de bosques de baja elevación que se encuentran en estadíos sucesionales tardíos (potencial hábitat de nidificación para estas aves) en cada cuenca. En cada uno de los tres años, el máximo número de individuos de B. marmoratus detectados estuvo positivamente correlacionado con la cantidad de bosque sucesional tardío; luego de controlar por el área de las cuencas esta relación persistió en 1999 y 2000. Durante todos los años, los conteos de B. marmoratus mediante radares no se correlacionaron con la cantidad combinada de tierras cosechadas, desarrolladas y agrícolas. El número de individuos de B. marmoratus aumentó con el área núcleo de bosque sucesional tardío y con el aumento de la proximidad entre parches, y decreció con el aumento de la cantidad de borde en los parches sucesionales tardíos. El número de aves no se correlacionó con el porcentaje de bosque sucesional tardío, densidad y área de parches, densidad de calles, ni diversidad total de todos los tipos de hábitats en el paisaje. Ni el número máximo ni el promedio de individuos de B. marmoratus que volaron en dirección tierra adentro diferió entre años; el efecto del año fue pequeño en comparación con el efecto del hábitat o del número de aves. Nuestros resultados sugieren que los cambios en la cantidad o distribución de hábitat para la nidificación deberían resultar en cambios detectables en el número de individuos de B. marmoratus a la escala individual de cada cuenca. Por lo tanto, la cantidad y distribución de hábitat para nidificación puede jugar un papel importante en la regulación de poblaciones de B. marmoratus, lo cual apoya la idea que proveer de hábitat para nidificación es una técnica efectiva para la conservación y restauración de esta especie.

RADAR-BASED MONITORING OF MARBLED MURRELETS

Abstract We used radar to measure daily, monthly, and annual patterns of Marbled Murrelet (Brachyramphus marmoratus) abundance and movements at 12 major river valleys in the Olympic Peninsula of Washington. Landward movements of murrelets peaked from ∼75 min to ∼20 min before sunrise, followed by a seaward exodus from ∼20 min before sunrise to ∼65 min after sunrise. This general pattern of a landward movement followed by a seaward exodus varied little, but the timing of the seaward exodus gradually became later from May to July. Within a morning, numbers of landward radar targets averaged twice the numbers of seaward targets, and morning counts were approximately five times evening counts. Species identification error rates were lower for landward radar counts than for seaward counts. Radar counts varied through the season, with numbers increasing from May to July, then dropping in August. Seaward counts were more variable than landward counts. There was wide overlap among months in the amount of daily variation in both landward and seaward counts. Radar appears to be a powerful, cost-effective, and non-intrusive tool that can establish an index of abundance for murrelets at specific inland breeding areas.

Genetic analyses of historic and modern marbled murrelets suggest decoupling of migration and gene flow after habitat fragmentation

The dispersal of individuals among fragmented populations is generally thought to prevent genetic and demographic isolation, and ultimately reduce extinction risk. In this study, we show that a century of reduction in coastal old-growth forests, as well as a number of other environmental factors, has probably resulted in the genetic divergence of marbled murrelets (Brachyramphus marmoratus) in central California, despite the fact that 7 per cent of modern-sampled murrelets in this population were classified as migrants using genetic assignment tests. Genetic differentiation appears to persist because individuals dispersing from northern populations contributed relatively few young to the central California population, as indicated by the fact that migrants were much less likely to be members of parent–offspring pairs than residents (10.5% versus 45.4%). Moreover, a recent 1.4 per cent annual increase in the proportion of migrants in central California, without appreciable reproduction, may have masked an underlying decline in the resident population without resulting in demographic rescue. Our results emphasize the need to understand the behaviour of migrants and the extent to which they contribute offspring in order to determine whether dispersal results in gene flow and prevents declines in resident populations.

Characterizing dispersal patterns in a threatened seabird with limited genetic structure.

Genetic assignment methods provide an appealing approach for characterizing dispersal patterns on ecological time scales, but require sufficient genetic differentiation to accurately identify migrants and a large enough sample size of migrants to, for example, compare dispersal between sexes or age classes. We demonstrate that assignment methods can be rigorously used to characterize dispersal patterns in a marbled murrelet (Brachyramphus marmoratus) population from central California that numbers approximately 600 individuals and is only moderately differentiated (FST∼ 0.03) from larger populations to the north. We used coalescent simulations to select a significance level that resulted in a low and approximately equal expected number of type I and II errors and then used this significance level to identify a population of origin for 589 individuals genotyped at 13 microsatellite loci. The proportion of migrants in central California was greatest during winter when 83% of individuals were classified as migrants compared to lower proportions during the breeding (6%) and post‐breeding (8%) seasons. Dispersal was also biased toward young and female individuals, as is typical in birds. Migrants were rarely members of parent‐offspring pairs, suggesting that they contributed few young to the central California population. A greater number of migrants than expected under equilibrium conditions, a lack of individuals with mixed ancestry, and a small number of potential source populations (two), likely allowed us to use assignment methods to rigorously characterize dispersal patterns for a population that was larger and less differentiated than typically thought required for the identification of migrants.

Orientation of American Kestrel Nest Cavities and Nest Trees

Balgooyen (1976), in his Sierra Nevada study, showed that nest cavities of American Kestrels (Falco sparverius) face east significantly more often than expected, and that nest trees are most often located on east-facing slopes. He based his results on comparisons of observed frequency distributions to a uniform distribution. But American Kestrels, typical of most secondary cavity-nesting birds, use abandoned nest cavities excavated by woodpeckers. It is possible, therefore, that the nonrandom orientations of kestrel nest cavities and slope exposure reflect selection by the original nest excavators rather than by the kestrels. Some studies have reported nonrandom orientations of woodpecker nest cavities (Lawrence 1967, Conner 1975, Inouye 1976, Korol and Hutto 1984). If most available cavities or slopes faced east, the apparent preference by kestrels could be random selection of available cavities or trees. To test this possibility, I compared Balgooyens (1976) data on nest orientation to an independent sample of 105 nests of the two species whose nests kestrels most often use in California-Northern Flicker (Colaptes auratus) and Lewis Woodpecker (Melanerpes lewis; Raphael and White 1984). I collected data from 1975 to 1978 on the same study areas reported by Balgooyen (1976). My null hypotheses were that: (1) no difference existed in orientation of kestrel nest cavities compared to that of available cavities, and (2) slope exposures were equal for kestrel nest trees and available trees. I tested the hypotheses using Watsons U2 test (Batschelet 1965:35). Both hypotheses were rejected. Nest cavity orientation differed significantly from expected (U2105,58 = 0.307, P < 0.005), and slope exposures also differed from expected (U293,58 = 0.490, P < 0.005; Table 1). Available cavities were generally oriented in a northerly direction (mean azimuth = 14*; Table 1), whereas most kestrel cavities faced east-northeastward (mean angle = 59*). Angular dispersions, which measure the relative concentration of points around the mean, were similar among nests and available trees for both cavity orientation and slope exposure (Table 1). Examination of differences between percentages of kestrel and woodpecker nests for each of the eight directions showed the greatest deviation for east-facing cavities and slopes (Table 1), supporting Balgooyens original observations. Balgooyen (1976) speculated that nest cavities facing eastward might offer thermoregulatory advantages because of warmth of the morning sun and protection from storms and hot afternoon temperatures. These considerations should also apply to the woodpeckers that excavated the nests. If so, most woodpecker nests should have been excavated with east exposures. It is possible that woodpe kers excavated cavities at the place around t e tru k where decay conditions were best for nest excavation. In the present study area, however, both Lewis Woodpecke s and Northern Flickers excavated nests in trees that were decayed throughout (Raphael and White 1984). Therefore, it is unlikely that their nests were oriented in relation to variable decay characteristics of the trees. While these results do not rule out the possibility that kestrels choose cavities to maximize thermal advantages, further study would be necessary before accepting such an explanation. The apparently nonrandom selection of east-facing cavities by kestrels nevertheless cannot be attributed to cavity availability.

Regional population monitoring of the marbled murrelet: field and analytical methods.

The marbled murrelet (Brachyramphus marmoratus) ranges from Alaska to California and is listed under the Endangered Species Act as a threatened species in Washington, Oregon, and California. Marbled murrelet recovery depends, in large part, on conservation and restoration of breeding habitat on federally managed lands. A major objective of the Northwest Forest Plan (the Plan) is to conserve and restore nesting habitat that will sustain a viable marbled murrelet population. Under the Plan, monitoring is an essential component and is designed to help managers understand the degree to which the Plan is meeting this objective. This report describes methods used to assess the status and trend of marbled murrelet populations under the Plan.

TRENDS IN RADAR-BASED COUNTS OF MARBLED MURRELETS ON THE OLYMPIC PENINSULA, WASHINGTON, 1996–2004

Abstract ABSTRACT The Marbled Murrelet (Brachyramphusmarmoratus) is a highprofile, federally threatened seabird, but noreliable estimates of population trends at inlandbreeding areas exist for this species. We conductedland-based radar studies of Marbled Murrelets at3–7 sites on the Olympic Peninsula,Washington, in 1996–2002 and 2004 to estimatepopulation changes and to examine relationshipsbetween our counts and oceanographic conditions,murrelet productivity, and regional at-sea countsof murrelets. Morning radar counts of murreletsvaried significantly among and within sites but didnot decline from 1996–2004, suggesting thatthe inland breeding population of murrelets isstable in this area. A retrospective power analysisindicated that we had a 25% and 56%chance of detecting 2% and 4% annualdeclines, respectively. Thus, if relatively smallannual declines did occur during our study period,there is a high probability that they would havegone undetected, even though they could add up to abiologically important decline over time. It isunlikely that murrelets on the Olympic Peninsuladeclined by ≥6% annually, however,because retrospective analyses indicated that powerto detect such declines was >88%. Therewas no significant relationship between radarcounts and at-sea counts or productivity ofmurrelets in the nearby San Juan Islands during thestudy period. We also did not detect a relationshipbetween radar counts and mean sea-surfacetemperatures or the Northern Oscillation Index,suggesting that variation in oceanographicconditions (e.g., the strong 1998 ElNiño event) was not associated withvariation in morning radar counts of MarbledMurrelets. A prospective power analysis indicatedthat small (2%–4%)annual declines could be detected with reasonablyhigh power (≥80%) with thecurrent radar sampling design by extending thestudy to 11–15u2005years.

Marine Habitat Selection by Marbled Murrelets (Brachyramphus marmoratus) during the Breeding Season.

The marbled murrelet (Brachyramphus marmoratus) is a declining seabird that is well-known for nesting in coastal old-growth forests in the Pacific Northwest. Most studies of habitat selection have focused on modeling terrestrial nesting habitat even though marine habitat is believed to be a major contributor to population declines in some regions. To address this information gap, we conducted a 5-year study of marine resource selection by murrelets in Washington, which contains a population experiencing the steepest documented declines and where marine habitat is believed to be compromised. Across five years we tracked 157 radio-tagged murrelets during the breeding season (May to August), and used discrete choice models to examine habitat selection. Using an information theoretic approach, our global model had the most support, suggesting that murrelet resource selection at-sea is affected by many factors, both terrestrial and marine. Locations with higher amounts of nesting habitat (β = 21.49, P < 0.001) that were closer to shore (β = -0.0007, P < 0.001) and in cool waters (β = -0.2026, P < 0.001) with low footprint (β = -0.0087, P < 0.001) had higher probabilities of use. While past conservation efforts have focused on protecting terrestrial nesting habitat, we echo many past studies calling for future efforts to protect marine habitat for murrelets, as the current emphasis on terrestrial habitat alone may be insufficient for conserving populations. In particular, marine areas in close proximity to old-growth nesting habitat appear important for murrelets during the breeding season and should be priorities for protection.