Lynn W. Lougheed

Intraspecific Variation in Commuting Distance of Marbled Murrelets (Brachyramphus marmoratus): Ecological and Energetic Consequences of Nesting Further Inland

Abstract Radio transmitters were deployed on Marbled Murrelets (Brachyramphus marmoratus) at Desolation Sound, British Columbia, Canada, during the 1998 breeding season to assess individual variation in distance birds nested from foraging areas, and potential energetic and ecological consequences of commuting those distances. Radio-tracking from a helicopter was used to locate nests, and tracking from the air and boats was used to locate murrelets on the water. Twenty-three nests were found, with active incubation at 16, and active chick-rearing at 12. A minimum of 3 nests fledged chicks, 9 were failures, and 11 were unknown. Nests were at an elevation of 806 ± 377 m and a distance of 39.2 ± 23.2 km (range 12–102 km) from locations on the water. Birds spent an estimated 1.2 ± 0.7 h per day commuting to and from nests (range 0.3–3.5 h per day). It was estimated that birds expended 3,883 ± 2,296 kJ (range 1,200–10,144 kJ) over the breeding season when commuting to those nests, which was 5–41% of their estimated field metabolic-rate during the breeding season. There was no relationship between distance to nests and breeding success. Either Marbled Murrelets can accommodate that additional energy expenditure, or reduce commuting costs by modifying their foraging behavior. They may forage closer to nest sites when provisioning chicks, thereby reducing commuting costs with a payload, or alter nest visitation rates in relation to distance they nest from foraging areas. Nests further inland may also confer advantages that compensate for the added commuting, or birds might replenish body reserves at the end of the breeding season.

The Reliability of Brood Patches in Assessing Reproductive Status in the Marbled Murrelet: Words of Caution

Abstract The assumption that brood patches identify incubating birds is a pervasive one in avian literature, and as a result, brood patches are often used to infer breeding status. Although the developmental stages of the brood patch with specific reproductive stages in passerines have been described, this information for seabirds is not often reported. Thus, for birds whose breeding activities are not easily observed, it is difficult to confirm (1) that it is valid to assume that a bird which has some stage of brood patch is a nester or putative nester, and (2) whether specific stages of brood patch development reflect specific stages of the breeding cycle. We tested the utility of brood patch scores to infer breeding status in a non-colonial seabird, the Marbled Murrelet (Brachyramphus marmoratus), a species always captured away from the nest site. We confirmed the breeding status of murrelets with brood patches, and assessed the specific stages of brood patch development to the timing of egg-production (using a physiological analysis) and the onset of incubation (using radio telemetry). Murrelets with brood patches were not always nesters or putative nesters (58% of birds with brood patches were producing eggs, and 56% of radio-tagged birds with brood patches began incubation), and brood patch score did not predict which birds were more likely to become egg-producers or incubators. Specific brood patch stages did not always correlate with specific breeding stages (e.g., the brood patch of egg-producers ranged from absent to fully-developed). Birds with fully developed brood patches took from 3-30 days to start incubation. Brood patch development accurately depicted the average population incubation time, but we caution against using brood patches to predict the timing of an individual breeding attempt, and suggest that when possible, researchers should try to confirm breeding activities using other methods.

Estimating statistical power to evaluate ongoing waterfowl population monitoring

The probability of failing to detect a trend when 1 exists has been considered only rarely in the interpretation of monitoring studies. Retrospective power analysis accomplishes this assessment. We apply retrospective power analysis to evaluate both population trends and survey design in the waterfowl surveys conducted by the Canadian Wildlife Service and others around Riske Creek, British Columbia. Eleven of 18 species showed long-term (17 yr) and short-term (10 yr) trends. For the remaining 7 species, the long-term analysis had sufficient power (0.8) to have detected at least a 5% annual change, had 1 existed, which supported the conclusion that little change occurred. However, statistical power and detectable effects varied considerably among species, with a range of 3-14 years of data needed to be able to detect a 5% annual trend. When we used the shorter-term dataset, power was reduced below acceptable levels for 4 of the 7 species failing to show a trend. It would be a mistake to conclude that the numbers of these 4 species were not changing. Statistical power was highest for the species for which the surveys were originally designed, Barrows goldeneye (Bucephala islandica) and mallards (Anas platyrhynchos), which had narrow confidence intervals and relatively small minimum detectable trends. In contrast, blue-winged teal (Anas discors), gadwall (Anas strepera), green-winged teal (Anas crecca), northern pintail (Anas acuta), and northern shoveler (Anas clypeata) had relatively large minimum detectable trends and wide confidence intervals. Much of the power of these surveys was due to repeated surveying within seasons. For most species, power increased substantially by including up to 4 surveys as replicate observations within a year, but power increased little when data from a fifth or sixth survey were included.

TECHNIQUES FOR INVESTIGATING BREEDING CHRONOLOGY IN MARBLED MURRELETS, DESOLATION SOUND, BRITISH COLUMBIA

Abstract We used several methods to study the chronology and synchrony of breeding events of the Marbled Murrelet (Brachyramphus marmoratus) population at Desolation Sound, British Columbia, from 1996 to 1998. The timing of breeding events varied among years; on average the breeding season lasted from 21 April to 5 September. We assessed the biases of each method used by comparing the results to the estimate of the integrated breeding chronology. Counts of hatch-year birds at sea were biased toward earlier breeders, missing an estimated 24% of the fledglings. Two other methods, physiological analysis of the yolk precursor vitellogenin from blood samples and monitoring by radio-telemetry could produce a complete distribution of breeding events if sampling were done throughout laying. Observations in the forest, date of first observation of a fledgling at sea during the breeding season, and fish-holding behavior produced insufficient data to be used as sole indicators of breeding chronology of this species. In general, breeding synchrony in alcids, assessed using data from a literature review, was unrelated to feeding habits but increased with latitude (41% of the variation was explained by latitude). Marbled Murrelets, however, bred less synchronously than predicted for an alcid at this latitude (50°N). Técnicas para Investigar la Cronología Reproductiva de Brachyramphus marmoratus en Caleta Desolación, Columbia Británica Resumen. Utilizamos varios métodos para investigar la cronología reproductiva de la población de Brachyramphus marmoratus en la Caleta Desolación de la Columbia Británica desde 1996 a 1998. Encontramos variaciones temporales en la época reproductiva entre años. En promedio, la estación reproductiva se extendió del 21 de abril al 5 de septiembre. Evaluamos el sesgo de los métodos utilizados comparando los resultados individuales con los resultados de la cronología obtenida al integrar todos los métodos. Los conteos de juveniles en el mar estuvieron sesgados hacia aquellas aves que anidan temprano, no detectando aproximadamente 24% de los juveniles producidos en la estación reproductiva. Los otros dos métodos, análisis fisiológico de muestras de sangre para detectar el precursor de vitelogenina en la yema y monitoreo por telemetría, podrían producir una distribución completa de las etapas reproductivas siempre que el muestreo se lleve a cabo a lo largo de todo el período de puesta. Las observaciones directas en los sitios de anidación, la fecha de la primera observación de juveniles en el mar y las observaciones de aves con pescado en el pico produjeron datos insuficientes para ser considerados indicadores únicos de la cronología reproductiva para esta especie. Con base en una revisión bibliográfica se investigó la sincronía reproductiva en álcidos, encontrándose que ésta no está relacionada con hábitos alimenticios pero que aumenta con la latitud (41% de la variación fue explicada por cambios latitudinales). Sin embargo, B. marmoratus se reprodujo menos sincrónico que lo predicho para un álcido a esta latitud (50°N).

LOCAL SURVIVAL OF ADULT AND JUVENILE MARBLED MURRELETS AND THEIR IMPORTANCE FOR ESTIMATING REPRODUCTIVE SUCCESS

Abstract Juvenile ratios estimated using numbers of hatch year (HY) and after-hatch-year (AHY) Marbled Murrelets (Brachyramphus marmoratus) counted concurrently during at-sea surveys have been used to estimate fecundity in this species. These “concurrent” juvenile ratios assume that HY birds remain in an area, and are likely biased because they do not account for potential differences in emigration rate of HY and AHY birds. We studied the emigration rates of adult and juvenile Marbled Murrelets marked with radio-transmitters. Juveniles had a high emigration rate compared to adults. The weekly local survival rate (ϕ) of newly radio-tagged HY birds was 27%. AHY local survival was 95% during incubation and early chick rearing, suggesting a resident population during the breeding season. We calculated juvenile ratios from 1996–1998 using (1) HY counts corrected for emigration and mean AHY counts around the breeding season peak, and (2) HY and AHY counts from concurrent at-sea surveys. The average “corrected” juvenile ratio (0.13 ± 0.05 SE) was higher than the “concurrent” juvenile ratio (0.04 ± 0.02 SE) but lower than estimates of fecundity from nest monitoring (0.18–0.22). Low juvenile ratios from at-sea surveys could result either from an unknown proportion of nonbreeding birds in the population, or, more likely, from differences in the at-sea distribution of AHY and HY birds. Fluctuation in the timing of the peak number of AHY birds across years might result in an uncorrectable bias in the counts. Because of biases and potential problems, caution is needed when interpreting juvenile ratios from at-sea surveys. Supervivencia Local de Brachyramphus marmoratus Adultos y Juveniles y su Importancia para Estimar Éxito Reproductivo Resumen. Utilizamos los cocientes entre individuos juveniles (nacidos en un año) y adultos (nacidos en años anteriores) de Brachyramphus marmoratus, censados simultáneamente durante conteos en el mar, para estimar la fecundidad de esta especie. Estos cocientes “simultáneos” de individuos asumen que los juveniles permanecen en una misma área, y podrían estar sesgados ya que no toman en cuenta diferencias en las tasas de migración de juveniles y adultos. Estudiamos las tasas de emigración de individuos juveniles y adultos de B. marmoratus marcados con radio-transmisores. Los juveniles tuvieron una tasa alta de emigración comparada con los adultos. La tasa de supervivencia local semanal (ϕ) para juveniles fue del 27%. La tasa de supervivencia local para adultos durante la incubación e inicio de la cría de polluelos fue del 95%, sugiriendo que se trata de una población residente durante la estación reproductiva. Calculamos el cociente entre juveniles y adultos para 1996–1998 utilizando (1) conteos de juveniles corregidos por emigración y promedio de adultos contados durante el pico de la estación reproductiva, y (2) juveniles y adultos contados simultáneamente durante los censos. El cociente “corregido” promedio entre juveniles a adultos (0.13 ± 0.05 EE) fue mayor que el cociente “simultáneo” (0.04 ± 0.02 EE) pero menor que las estimaciones de fecundidad obtenidas por medio del monitoreo de nidos (0.18–0.22). Los bajos cocientes obtenidos de conteos en el mar podrían explicarse por la presencia de una proporción desconocida de aves no-reproductivas en la población, o, más probablemente, por diferencias existentes en la distribución de juveniles y adultos en el mar. Fluctuaciones anuales en la sincronización del período pico de la estación reproductiva podrían introducir error a los conteos de adultos. Debido a estos sesgos y problemas potenciales, es importante interpretar con cautela los cocientes entre juveniles y adultos obtenidos de conteos en el mar.

Breeding chronology of Marbled Murrelets varies between coastal and inshore sites in southern British Columbia

Abstract We used four methods to compare the breeding chronologies of Marbled Murrelet at two sites at similar latitudes in British Columbia: Desolation Sound on the mainland, inshore of the Strait of Georgia, and Clayoquot Sound on the west coast of Vancouver Island. At both sites, we estimated breeding chronologies from the timing of (1) nest initiation dates determined by radio-telemetry, (2) the chick feeding period determined from observations of fish-holding adults, (3) hatch dates determined from observations of juveniles on the water, and (4) brood patch scores determined from captured birds. At Desolation Sound, these methods each produced a similar distribution of nesting dates, but at Clayoquot Sound, the distribution of nesting dates of radio-tracked birds were substantially biased towards later nests. Despite these methodological difficulties, we found that Marbled Murrelets at Desolation Sound bred ca. 30 d later than at Clayoquot Sound. Regional differences in breeding chronology of this magnitude, if not properly calibrated, would bias estimates of peak inland activity, and should be considered in forestry operations, the interpretation of census data, and the design of monitoring programs.

DO TWO MURRELETS MAKE A PAIR? BREEDING STATUS AND BEHAVIOR OF MARBLED MURRELET PAIRS CAPTURED AT SEA

Abstract Marbled Murrelets (Brachyramphus marmoratus) observed at sea usually are in pairs throughout the year. Although it has been assumed that these pairs are mates, this assumption has not been formally examined. Using data from three study sites during the breeding seasons of 1997–2001, we found that 92% of the birds that were paired at capture were of male-female pairs, and that paired females were more likely (73%) to be producing eggs than were single females (8%). Fourteen of fifteen pairs were tracked to a single nest location per pair. No pair members caught at sea were found breeding at separate nest sites. One pair was caught in two successive seasons, suggesting that at least some pairs are long lasting. Notably, pair members breeding together and radio tracked throughout the summer were detected without their breeding partners for 77% of the time. Thus, while pairs of Marbled Murrelets observed at sea most likely are members of a breeding pair, single murrelets observed at sea should not be assumed to be unpaired or nonbreeders.

Morphometric Variation in Marbled Murrelets, Brachyramphus Marmoratus, in British Columbia

Morphometrics (culmen length, bill height, bill width, wing chord length, and tarsus length) were taken on 664 marbled murrelets at Desolation Sound and Mussel Inlet, British Columbia, during 1994 to 1997, in order to assess morphological differences within and between populations and the accuracy of a discriminant function analysis to identify the sex of birds. An assessment of interand intra-observer variability in measurements was also made. Significant inter-observer effects and some intra-observer effects were found. Data from recaptured murrelets indicated they had decreased in size with age, which was attributed to interobserver effects. Wing chord length had the highest measurement error (66.8%) among observers and tarsus length had the lowest error (36.8%). Deviations of measurements from the mean were compared among years and sites. No inter-annual differences were detected in any morphometric at Desolation Sound. Significant differences in culmen length, wing chord length, and tarsus length were found between birds from Mussel Inlet and Desolation Sound, which might indicate discrete populations. The degree of sexual dimorphism in this species was small (measurements of females average 98% of corresponding measurements of males) and discriminant function analysis revealed only about a 70% success rate in allocating birds to sex; therefore, its widespread use in this species is not recommended. Future studies of marbled murrelets, or other avian species, which involve large numbers of personnel, should incorporate extensive training of all observers, with data continually cross-checked in order to minimize intraand inter-observer differences in measurements.