Daniel D. Gibson

Movements of Birds and Avian Influenza from Asia into Alaska

Despite involvement of large numbers of birds, the delivery rate of Asian-origin viruses to North America through Alaska is apparently low.

PHYLOGEOGRAPHY OF THE MALLARD (ANAS PLATYRHYNCHOS): HYBRIDIZATION, DISPERSAL, AND LINEAGE SORTING CONTRIBUTE TO COMPLEX GEOGRAPHIC STRUCTURE

Abstract Population genetic variation in Mallards (Anas platyrhynchos; n = 152) from Western Russia, North Asia, the Aleutian Islands, and mainland Alaska was investigated using 667 base pairs of the 5′-end of the mitochondrial DNA (mtDNA) control region. DNA sequencing revealed two clades that correspond to Avise et al.’s (1990) group A and B mtDNA haplotypes. Group A haplotypes (80.3%) were wide- spread in all localities from Western Russia to Alaska. Group B haplotypes (19.7%), by contrast, were found primarily in mainland Alaska, where they occurred at high frequency (77.4%), but they also occurred at low frequencies (declining east to west) in the Aleutian Islands (11.8%) and the Primorye region of North Asia (4.4%). Group B haplotypes were not observed in Western Russia or elsewhere in North Asia outside Primorye. Consequently, Mallards exhibited substantial genetic structure between Old World and New World (ΦST = 0.4112–0.4956) but possessed little genetic structure within the Old World continental area (ΦST = 0.0018). Nonetheless, when only group A haplotypes were included in the analysis, Mallards from the Aleutian Islands differed (albeit with low levels of divergence) from each of the other three sampled regions in the Old World and New World (ΦST = 0.0728–0.1461, P < 0.05). Mallards inhabit the Aleutian Islands year-round, so these insular populations may be isolated from Asian and North American populations that occur in the Aleutian Islands only during migration. Overall weak phylogeographic structure and low genetic differentiation within Asia, and between Asia and North America when only group A haplotypes were evaluated, is probably explained by large long-term population sizes and significant intra-continental dispersal. The coexistence and nonrandom distribution of two divergent mtDNA haplotype lineages in Alaska, the Aleutian Islands, and the Primorye region of North Asia, but not in Western Russia or elsewhere in North Asia, is consistent with historical and contemporary hybridization and incomplete sorting of A and B mtDNA haplotype lineages in Mallards and closely related species inhabiting the Old World and New World.

The Asia-to-America Influx of Avian Influenza Wild Bird Hosts Is Large

Abstract Recent literature has underestimated the number and taxonomic diversity of wild birds moving between Asia and North America. Our analyses of the major avian influenza (AI) host groups show that fully 33 species of waterfowl (Anatidae), 46 species of shorebirds (Charadriidae and Scolopacidae), and 15 species of gulls and terns (Laridae) are involved in movements from Asia to Alaska across northern oceans (Table 1). Our data suggest that about 1.5–2.9 million individuals in these important host groups move from Asia to Alaska annually. Among all of the host groups we consider most relevant for AI virus movement models in this region (waterfowl, shorebirds, and gulls and terns), it seems likely that thousands of AI-infectious birds may be involved in annual Asia-to-America migrations. Importantly, host availability in Alaska once these vectors arrive is also very high, representing at least 5–10 times more birds and infectious birds than the host populations moving from Asia to North America. Incorporating our data into a recent model of the global spread of the highly pathogenic H5N1 suggests that wild birds are a more likely source of this strain being brought into the United States than trade in domestic birds, although the latter remain a numerically more probable source of introduction into the New World. Our results should help in defining the key taxonomic, geographic, and seasonal factors involved in this complex intercontinental association of wild bird AI hosts. The next steps are to determine infection rates of low pathogenicity and highly pathogenic viruses among these hosts and to incorporate these into dynamic models.

A parapatric propensity for breeding precludes the completion of speciation in common teal (Anas crecca, sensu lato)

Speciation is a process in which genetic drift and selection cause divergence over time. However, there is no rule dictating the time required for speciation, and even low levels of gene flow hinder divergence, so that taxa may be poised at the threshold of speciation for long periods of evolutionary time. We sequenced mitochondrial DNA (mtDNA) and eight nuclear introns (nuDNA) to estimate genomic levels of differentiation and gene flow between the Eurasian common teal (Anas crecca crecca) and the North American green‐winged teal (Anas crecca carolinensis). These ducks come into contact in Beringia (north‐eastern Asia and north‐western North America) and have probably done so, perhaps cyclically, since the Pliocene–Pleistocene transition, ∼2.6 Ma, when they apparently began diverging. They have diagnosable differences in male plumage and are 6.9% divergent in the mtDNA control region, with only 1 of 58 crecca and 2 of 86 carolinensis having haplotypes grouping with the other. Two nuclear loci were likewise strongly structured between these teal (Φst ≥ 0.35), but six loci were undifferentiated or only weakly structured (Φst = 0.0–0.06). Gene flow between crecca and carolinensis was ∼1 individual per generation in both directions in mtDNA, but was asymmetrical in nuDNA, with ∼1 and ∼20 individuals per generation immigrating into crecca and carolinensis, respectively. This study illustrates that species delimitation using a single marker oversimplifies the complexity of the speciation process, and it suggests that even with divergent selection, moderate levels of gene flow may stall the speciation process short of completion.

THE BIRDS OF ST. MATTHEW ISLAND, BERING SEA

Abstract St. Matthew Island (60° 24′ N, 172° 42′ W) and its small nearby satellites, Hall Island and Pinnacle Rock, are isolated in the northcentral Bering Sea. This infrequently visited location occupies a geographic position with a deep Bering Land Bridge history and is in an area of interdigitation of the Old World, New World, and Beringian avifaunas. It is known for its three Beringian endemics, a bird (McKay’s Bunting, Plectrophenax hyperboreus), a small mammal, and a plant. This level of endemism is striking for a high-latitude island. The only previous summary of the avifauna of St. Matthew island (Hanna 1917) included 37 species. Our report considers more than 125 species and synthesizes data on presence and absence, abundance, and phenology. Because visits have been infrequent and concentrated during summer, our understanding of migration in this region remains poor, but the area is clearly affected by both the Old and New world migration systems. There is sufficient evidence to show that some profound changes among the island’s breeding birds have occurred during the past century. In particular, the breeding range of Glaucous-winged Gulls (Larus glaucescens) has been extended north to include St. Matthew, a change that is correlated with a northward shift in the extent of sea ice (Maslanik et al. 1996). King and Common eiders (Somateria spectabilis and S. mollissima) also have shown substantial changes in summer abundance. Other changes in the summer avifauna (e.g., among shorebirds) may reflect the dynamics of edge-of-range phenomena. Because of its central position in a region undergoing profound climate change and its demonstrated track record in showing avifaunal shifts, St. Matthew Island may represent an important bellwether for monitoring the biological effects of further climate change in the northern Bering Sea.

Individual and environmental effects on egg allocations of female Greater Sage-Grouse

ABSTRACT The average number of eggs in a clutch and the size of those eggs play a role in individual fitness. We explored sources of variation in egg allocations of female Greater Sage-Grouse (Centrocercus urophasianus) in the American Great Basin over a 10-yr period, as well as range-wide variation in clutch size, using our data and other published values. We tested for environmental and individual effects on clutch size (n = 390) and egg volume (n = 2,486) in a mixed-modeling framework, with random-effect terms that described variation among individual females (i.e. heterogeneity) and allowed us to calculate repeatability for clutch and egg size. The strongest influence on clutch size was the timing of nest initiation, which varied by as much as 67 days within years and showed a negative linear relationship with clutch size. Once this pervasive effect was accounted for, we also found positive effects of annual precipitation and nest-site elevation. In wetter years and at more productive high-elevation sites, females laid larger clutches, which suggests that some degree of large-scale resource availability affects clutch size. The fixed effects in our models explained ∼34% of the total variance in clutch size, and individual random effects explained an additional 15% (repeatability = 0.15). In contrast to clutch size, little measurable variation in egg volume could be attributed to the fixed effects we considered, and ∼60% of the variance in egg volume was associated with random effects (repeatability = 0.59). Prenesting female body condition influenced clutch size, and this effect was most pronounced for replacement clutches. We found repeatability for clutch and egg size to be within the range of published estimates for other avian taxa. Across studies, mean clutch size increased with latitude, demonstrating that Greater Sage-Grouse follow geographic patterns in clutch size that are consistent with other avian taxa.

Observer effects strongly influence estimates of daily nest survival probability but do not substantially increase rates of nest failure in Greater Sage-Grouse

ABSTRACT Researchers have long recognized that the process of observing nests may influence nest success by increasing depredation risk or causing females to abandon nests. The effects of observer-related nest abandonment may also reduce estimates of daily nest survival when time to nest fate is reduced and the average nest exposure period within the sample becomes shorter. We used an 8-yr record of observer visitations of nesting female Greater Sage-Grouse (Centrocercus urophasianus) in central Nevada, USA, to assess whether observers influenced either the probability of daily nest survival or the overall probability of nest success. Because nest success is influenced by factors other than visitation, we also accounted for the overall quality of a nest (i.e. probability of success in the absence of observer effects) based on potential confounding factors. Nest visitation (no flushing) had no effect on daily nest survival, regardless of nest quality or female age. Flushing a female from a nest substantially lowered the probability of the nest surviving the following day (maximum ~0.22). When considered in the context of the entire nest exposure period, however, flushing a female once produced only a marginal reduction in overall nest success (~0.015). Additionally, females that were younger, or that were associated with low-quality nests, were more likely to abandon the nest after flushing, compared with older females or those associated with higher-quality nests. Observer-related abandonment, however, introduced a negative bias (~0.07) into estimates of overall nest survival by reducing the average timing of nest fate and thereby lowering daily nest survival. Our results suggest that the act of flushing female Greater Sage-Grouse may bias estimates of nest survival low, but this is due to an effect on estimates of daily nest survival, rather than an actual influence on the probability of nest fate.

Prefledging Diet is Correlated with Individual Growth in Greater Sage-Grouse (Centrocercus urophasianus)

ABSTRACT. The period of growth prior to fledging is a critical life stage for most birds, and shifts in diet during ontogeny may affect growth and development. We used nitrogen (&dgr;15N) stable isotopes in feather tissue to quantify dietary composition and evaluate the relationship between diet and growth in prefledging Greater Sage-Grouse (Centrocercus urophasianus). Sequential sampling of &dgr;15N from feather tissue that was synthesized throughout growth allowed us to evaluate changes in plant versus invertebrate contributions to chick diet during the first 28 days posthatch. Feathers became depleted in &dgr;15N throughout growth, and Bayesian mixing models suggested that the proportional contribution of invertebrate nitrogen declined with chick age. We estimate that invertebrate contributions to the protein in chick diets decreased from 39% at 1 week to 23% at 4 weeks of age, which is consistent with previous research on sage-grouse that used traditional diet-sampling methods. Chicks with feather &dgr;15N values that spanned a larger range, but had an intermediate mean, had the longest tarsi and greatest mass at 28 days. These chicks also displayed a more rapid transition to herbivory during the prefledgling period. These patterns are consistent with greater importance of invertebrates during early growth but also suggest that a rapid transition to a more herbivorous diet ultimately results in the highest growth rates. Sequential sampling of feather &dgr;15N provided useful information on temporal patterns in chick diet that were directly relatable to growth during the prefledging stage, and we encourage replication of our approach in other systems.

Biases in nest survival associated with choice of exposure period: A case study in North American upland game birds

ABSTRACT Estimated probability of daily nest survival is commonly used to derive cumulative nest survival for a specified nest-exposure period. For many species of birds, the presence of a parent is an important cue used by researchers to locate nests, but in some cases nest detection rates are reduced during egg laying, when parents spend a greater amount of time away from the nest. As a result, sample size becomes limited during the laying stage. Researchers must then choose between 2 alternative strategies for deriving cumulative nest survival, based on either (1) exposure length for only the incubation period or (2) exposure length for laying plus incubation. Both approaches carry implicit assumptions, the violation of which can result in bias. We reviewed recent literature and describe the extent to which these 2 strategies were used in studies of galliform birds (including grouse, quail, and Wild Turkey [Meleagris gallopavo]) in North America. We then evaluated the theoretical potential for bias under each approach across a range of daily nest survival probabilities and for 3 different life-history scenarios. The incubation-only strategy was most commonly applied, with 62% of publications reporting its use. We found that the incubation-only strategy was biased except under an assumption of zero nest failure during egg laying. Fewer studies reported using the laying-plus-incubation strategy, which was unbiased in situations where risk of failure was equivalent among laying and incubation stages. This strategy also minimized bias across the broadest range of situations, and accordingly we recommend its use where the daily survival rate during egg laying is unknown. We recommend that both the laying and incubation periods should be used to define the length of nest exposure when estimating cumulative nest survival, particularly for species with large clutches and long laying periods.

Heteropatric speciation in a duck, Anas crecca

Heteropatric differentiation is a mode of speciation with gene flow in which divergence occurs between lineages that are in sympatry and allopatry at different times during cyclic spatial movements. Empirical evidence suggests that heteropatric differentiation may prove to be common among seasonally migratory organisms. We examined genetic differentiation between the sedentary Aleutian Islands population of green‐winged teal (Anas crecca‐nimia) and its close migratory relative, the Eurasian, or Old World (OW), Anas c. crecca population, a portion of which passes through the range of nimia during its seasonal migrations. We also examined its relationship with the parapatric North American, New World (NW), A. c. carolinensis population. Sequence data from eight nuclear introns and the mtDNA control region showed that the nimia‐crecca divergence occurred much more recently than the deeper crecca‐carolinensis split (~83 000 years vs. ~1.1 Myr). Despite considerable spatial overlap between crecca and nimia during seasonal migration, three key predictions of heteropatric differentiation are supported: significant genetic divergence (overall mean Φst = 0.07), low gene flow (2Nem ~ 1.8), and an effective population size in nimia that is not especially low (Ne ~ 80 000 individuals). Similar levels of gene flow have come into nimia from carolinensis, but no detectable nuclear gene flow has gone out of nimia into either OW (crecca) or NW (carolinensis) populations. We infer that adaptations of these populations to local optima in different places (e.g. each matching their reproductive effort to different resource blooms) promote genetic isolation and divergence despite periods of sympatry between them, as the heteropatric model predicts.