THE MIGRATION OF PASSERINE NIGHT MIGRANTS ACROSS THE ENGLISH CHANNEL STUDIED BY RADAR

An account is given of the migration of British summer resident small passerine night migrants across the English Channel in spring and autumn, as detected by radar.
The main times of passage of each species have been determined from the trapping records of Dungeness Bird Observatory.
The tracks of the migrants are consistent with the view that they always head about NNW in spring and SSE in autumn but may be drifted by a cross-wind.
The wind-direction and speed had a paramount influence on the volume of migration in both spring and autumn. Temperature had no effect in autumn, and though there was more migration with warmer than cold weather in spring, this need not have been due to the influence of temperature as such.
Small reversed movements occurred, with southerly winds in autumn or, more doubtfully, with northerly winds in spring.     

Quantifying the robustness of first arrival dates as a measure of avian migratory phenology

As the climate changes, many long‐term studies have shown that the timing of bird migration is shifting, increasing the need for reliable measures of migratory phenology. Ideally, daily counts of birds at a site are used to calculate the mean arrival date (MAD) but, as this approach is not always possible and is very labour‐intensive, simpler metrics such as first arrival date (FAD) have commonly been used. Here, we examine the relationship between FAD and MAD in 28 summer migrant bird species over a 42‐year period (1970–2011) at Portland Bird Observatory, UK. Although significant correlations between FAD and MAD were detected, relationships were weak, particularly in long‐distance migrants. We suggest that FAD, although a simple and straightforward measure, is not particularly robust as a proxy for overall migratory phenology at a population level.     

DETECTION BY RADAR OF AUTUMN MIGRATION IN EASTERN SCOTLAND

Radar observations through one autumn in Aberdeenshire are described showing that more migration takes place in anticyclonic weather than transitional weather, and even less migration takes place in disturbed weather. More migration is detected by radar with following winds than with opposed winds.
Comparison of data collected in Norfolk and Aberdeenshire during one season at each shows that more migration is detected by radar in Norfolk, and westward movements, which are a feature of migration into Norfolk, appear in Aberdeenshire only when birds are first drifted northwards.
Dawn ascent and reorientation movements of birds in the northern North Sea are described, showing that changes in heading were consistently between S.W./S.S.W. and S.S.E. during the autumn studied.
Weather data, radar data and ground observer data from Aberdeenshire and the Isle of May Bird Observatory were analyzed and show again that the normal migration pattern is to fly high with following winds and low only with opposing winds as in Norfolk. However, the weather in Aberdeenshire was more disturbed than it had been in Norfolk, with the consequence that weather factors, other than wind, which affect the normal migration pattérn were found to be much more common.     

The effects of hatching date on timing of autumn migration in partial migrants – an individual approach

Timing of spring migration and breeding and their interaction with climate change has been widely studied in recent years, but the possible changes in timing of autumn migration have gained less attention. This work focuses on autumn migration and provides the first multi‐species individual‐based study of how hatching date affects the autumn migration date and migration age by using nestling ring data and re‐trappings of the same individuals during the autumn migration at the Hanko Bird Observatory, Finland. We studied three potentially multibrooded passerines (great tit, blue tit and coal tit) and two single‐brooded birds of prey (goshawk, sparrowhawk), all partially migratory short‐distance migrants. Individuals from late broods migrated at a younger age in all tit species and also in hawks the late hatched individuals tended to migrate at a younger age than the early‐hatched individuals. Late‐hatched individuals migrated later than early‐hatched individuals in blue and coal tits, where the latest hatchers represented second brood individuals. Based on our results, the time from hatching to autumn migration is not constant even among individuals of the same population. Our study indicates that climate warming induced advancement of avian breeding may cause changes in the timing of autumn migration through the frequency of second broods.     

Young and female‐biased irruptions in pygmy owls Glaucidium passerinum in southern Finland

Irruptive migrants often show biased sex and age ratio, and typically young females are the most abundant class participating in irruptions. Several hypotheses have been proposed to explain differential migration in birds. We examined these hypotheses in a sexually size‐dimorphic species (females being larger than males), the pygmy owl Glaucidium passerinum, whose migration behaviour has also been poorly documented. Migration data were collected at the Hanko Bird Observatory, SW Finland during 1979–2010. Pygmy owls showed large fluctuations in migration numbers between years. Most of the migrants were young birds and females migrated in larger numbers than males. Results support the ‘territory defence hypothesis’ since males showed weaker tendency to migrate despite the smaller body size, but the ‘dominance hypothesis’ was also supported (subordinate young outnumber dominant adults in migration numbers). Findings support the idea that in owl species, which are dependent on nesting cavities, males show lower migration behaviour than females, whereas the pattern is opposite in species which normally breed outside cavities. In addition, adults migrated later than young, likely because they need to moult remiges before departure. Early hatched young also migrated earlier than late hatched young, suggesting that more dominant young migrate first.     

Banding data reveal bias in age‐class sampling of songbirds during spring migration

Population age structure and vital statistics are important for understanding songbird demography and for developing conservation strategies. Field‐based estimates of survival rates based on mark–recapture methods are conservative because they are constrained by problems associated with detection probabilities and emigration. However, data collected at bird‐banding stations during spring and fall migration can potentially provide useful demographic information. I used banding data collected over a 6‐yr period (2005–2010) at Long Point Bird Observatory on the north shore of Lake Erie in Ontario, Canada, and Powdermill Avian Research Center in southeastern Pennsylvania, U.S.A., to determine if banding records could be used to estimate vital statistics for several species of songbirds. As reported in previous studies, I found the proportion of juveniles captured during fall migration to be unrealistically high to be representative of true proportions, especially at Long Point. The proportion of juvenile songbirds captured remained implausibly high during spring migration, with related estimates of longevity and generation time implausibly low and of fecundity implausibly high. Based on apparent adult survival estimates from the literature that suggest an average age structure for songbirds of >55% adults and <45% juveniles, I found that capture rates for juveniles during spring migration were at least twice as high as that for adults. A slower pace of spring migration by juveniles likely accounts for some of this bias. Because the data cannot be assumed to represent unbiased samples with respect to the age structure of populations, my results indicate that banding data collected at bird‐banding stations during migration are not suitable for use in demographic studies.     

Climate patterns and the stochastic dynamics of migratory birds

We analyse time series data of 17 bird species trapped at Ottenby Bird Observatory, Sweden, during spring migration 1972–1999. The species have similar demography but respond differently to variation in the North Atlantic Oscillation (NAO) – a strong determinant of winter climate in the northern Hemisphere. Species wintering in northern Europe, compared to species having winter quarters in the Mediterranean area, tend to respond positively to variation in NAO. The variation within each group is high due to wide-ranging winter-distribution in many species, probably smoothing out the effect of spatial variation in NAO. Whereas mild winters (high NAO) is benign for many – but not all – birds wintering in northern Europe, the effect of drier-than-normal conditions in the Mediterranean area during high NAO index winters are uncertain. The work presented here goes beyond simple correlative studies and help identifying which species that are most affected by variation in winter climate. This is a first important step that calls for a more mechanistic approach when analysing possible changes to climate change.     

Changes in the timing of spring and autumn migration in North American migrant passerines during a period of global warming

Butler (2003) used first arrival dates (FADs) of 103 migrant birds in northeastern USA and found that both long-distance migrants (LDMs; wintering south of the USA) and short-distance migrants (SDMs; wintering in the southern USA) arrived earlier in the second half of the 20th century than they had in the first, consistent with scenarios of global warming; the trend was stronger in SDMs. Using FADs to characterize migration systems can be problematic because they are data from one tail of a distribution, they comprise a mostly male population and they may not correlate well with the balance of the migration period. FADs also provide no information about autumn migration. This paper uses a banding dataset from Long Point Bird Observatory, Ontario, for 14 passerines for a period of global warming (1975–2000), taking these issues into account. The data were filtered to minimize effects of unequal netting effort (147 491 resulting records), and the passage dates then calculated in each season of each year for the 1st, 2nd and 3rd quartiles for regression analysis. Only two of 13 species analysed in the spring showed significantly earlier passage times, although the overall trend was towards earlier spring migration, especially among SDMs. Autumn responses were more prevalent, however, and in some cases more dramatic with six of 13 species showing delayed migration (four SDMs, two LDMs). Two LDMs exhibited earlier autumn migration. Where earlier spring migration occurred, both sexes appeared to contribute to the change. Where delayed migration occurred in autumn, both sexes and both adults and hatch-year birds appeared to contribute in at least some cases. The spring FAD results are consistent with those of Butler, but when the whole migration is considered, change is far from universal in spring and is in fact more substantial and complex in autumn.     

Kinship analysis of Pacific salmon: insights into mating, homing, and timing of reproduction

Multilocus microsatellite genotypes were used to infer kinship and relatedness in two species of Pacific salmon from three populations in Washington State. Even in the absence of direct genetic data from parents, clustering of individuals according to allele sharing and reconstruction of parental genotypes allowed resolution of full- and half-sib relationships among 135 chinook salmon (Oncorhynchus tshawytscha) sampled as preemergent juveniles from 14 redds in the Dungeness River. Inferred reproductive behaviors included single-pair matings, polyandry in which females mated with two to three males at a single redd, polygyny in which males mated with two females at different redds, use of two redds by a single female, and use of one redd site by two females. Greater average relatedness (rxy) in the upper reach of the Dungeness River implied within-reach homing of returning adults. In steelhead trout (O. mykiss), the frequency of related pairs (dyads) of mature individuals that migrated up Snow Creek less than a week apart was greater than expected for randomly chosen dyads, as was the frequency of steelhead dyads that were spawned on the same day in the Forks Creek hatchery. These results imply a heritable basis for upstream migration date and maturation date in steelhead trout.     

The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness crab Cancer magister Dana

We evaluate the potential competitive and predatory impacts of nonindigenous European green crab Carcinus maenas on native Dungeness crab Cancer magister in the northeast Pacific. The coastal estuaries of Washington State, USA, provide appropriate habitat for recently introduced green crab, yet these areas are important nursery grounds for Dungeness crab and contribute greatly to the coastal crab fishery. Juvenile Dungeness crabs are dependent on limited intertidal epibenthic shell for refuge habitat during early benthic life and experience increased mortality on open sand and mud as a result of predation by fish and birds. Early juveniles throughout the subtidal are similarly at risk due to predation by fish and especially adult conspecifics. Laboratory experiments and infrared video observations revealed that juvenile green crab displace Dungeness crab of equal size from shelters during one-on-one competition. Green crab also consistently win nocturnal foraging trials in which the species compete for fresh, damaged clams. Field and laboratory enclosure experiments show that juvenile Dungeness crab emigrate from oyster shell habitat as a result of competition and predation by adult green crab. Depending on the extent to which the two species overlap, interactions with the dominant nonindigenous species could have a negative influence on juvenile Dungeness crab survival and could conceivably impact recruitment to the fishery. However, current evidence indicates that the distribution of green crab in Washington State is far removed from nursery areas of Dungeness crab.     

Recent developments at Dungeness

FINDON, R. A., 1989. Recent developments at Dungeness . The most significant development pressures at Dungeness over the last three years are discussed, namely military training, aggregate winning, water industry, electricity generation, recreation and tourism. The future prospects for Dungeness are briefly reviewed, as are the changes to the area notified as a Site of Special Scientific Interest.     

Reviews

Book reviewed in this article: Erber , J., R. Menzel , H.-J. Pflüger , & D. Todt, eds. (1989): Neural mechanisms of behavior (Neurale Mechanismen des Verhaltens). Bischof , H.-J. (1989): Neuroethologie (Neuroethology). Uni-Taschenbücher 1473, Verlag Eugen Ulmer, Stuttgart. Reichert , H. (1990): Neurobiologie (Neurobiology). Georg Thieme Verlag, Stuttgart. Huber , F., T. E. Moore , & W. Loher, eds. (1989): Cricket behavior and neurobiology (Verhalten und Neurobiologie der Grillen). Lindauer , M. (1990): Botschaft ohne Worte. Wie Tiere sich verständigen (How animals communicate). Berthold , P. (1990): Vogelzug. Eine kurze, aktuelle Gesamtübersicht (Bird migration. A short up-to-date survey). Gwinner , E., ed. (1990): Bird migration. Physiology and ecophysiology (Vogelzug: Physiologie und Ökophysiologie). Alerstam , Th. (1990): Bird migration (Vogelzug). Crowcroft , P. (1991): Elton's ecologists. A history of the Bureau of Animal Population (Zur Geschichte der Populations-Forschung).     

Modeling spring migration patterns of scoters and loons in the Bay of Fundy

Populations of scoter and loon species that winter in the Atlantic are understudied in North America, but coastal observatories may provide the data required to fill some of the knowledge gaps. The migration of scoters and loons has been monitored at the Point Lepreau Bird Observatory (PLBO) in the Bay of Fundy every spring since 1996, but little peer-reviewed research based on the resultant database has been published. Using data collected over 18 years at the Bay of Fundy (2000–2017), our objectives were to (1) determine the most accurate method of modeling hourly migration rates for Surf (Melanitta perspicillata), White-winged (M. deglandi), and Black (M. americana) scoters, and Red-throated (Gavia stellata) and Common (G. immer) loons, and (2) assess trends in hourly migration rates for our five focal species to determine if the numbers of migrants passing PLBO have changed over time. We calculated hourly migration rates for each of our five focal species and evaluated drivers (i.e., timing and environmental conditions) of migration and annual trends using zero-inflated generalized linear mixed models (GLMMs). We found that drivers of migration differed among species. Specifically, hourly migration rates decreased with increasing tide height for all species except Red-throated Loons. In addition, hourly migration rates increased with increasing wind vector (i.e., a tailwind) for the three scoter species, but decreased with increasing wind vector for the two loon species. Scoter migration rates peaked daily between 11:00 and 13:00 UTC, but we found no daily peak for either loon species. Peak hourly migration rates of Black and Surf scoters occurred from 12 to 26 April, but migration rates of White-winged Scoters and both loon species continued to increase throughout our migration-monitoring window. Finally, we found no changes in hourly migration rates over time for any of our focal species, suggesting no changes in abundance over the 18 years of data collection. Our study reveals the importance and utility of long-term, coastal observation stations, and we recommend their continued funding and use as valuable sources of monitoring data.     

Why are there so many species of bumble bees at Dungeness?

WILLIAMS, P. H., 1989. Why are there so many species of bumble bees at Dungeness? Dungeness is unique in the British Isles in that it has more species of bumble bees than any other locality. Three ideas about what governs the number of species at a locality are examined by locking at patterns of flower visits at Dungeness in comparison with those at Shoreham, a species-poor locality also in Kent. The species of bumble bees that are present at Dungeness but absent from Shoreham show no association in their distributions among 2 km grid-squares in Kent with the species of food-plants that they prefer at Dungeness, nor is there any correlation between the diversity of bees and diversity of food-plants at Dungeness and Shoreham. From the information available, Dungeness is most likely to have more species of bumble bees because it has a particularly high density of the more nectar-rich flowers that bumble bees can use. Bumble bees feed most profitably from deep flowers because these contain more nectar than shallow flowers, although direct access to deeper flowers is ultimately limited by the length of each bee's proboscis. The distribution of worker proboscis lengths among species in the species-pool in Kent is clumped about a median of 7.9 mm. The best foraging conditions for the maximum number of species should be provided when flowers of similar depths are present in sufficiently large numbers for all foragers to make near-optimal flower choices. Although there is no difference in median between the distributions of the bees' proboscis lengths and the depths of the flowers they use at Dungeness, at Shoreham the flower depths used are shorter than the proboscis lengths. Among the food-plants at Dungeness, high densities of Teucrium scorodonia and Echium vulgare are likely to be especially important.     

Orfordness and Dungeness: a comparative study

FULLER, R. M., 1989. Orfordness and Dungeness: a comparative study . Dungeness originally developed as a shingle spit from Winchelsea, across the bay which now forms the Romney Marshes and, 700–800 years ago, probably had its distal end between New Romney and Hythe. The structure seems to have been very similar to present-day Orfordness. Then a breach at the spit's origin produced an abrupt change in accretion and erosion patterns with the eventual development of the present-day cuspate foreland. It would seem that Orfordness is on the verge of such a breach, which is prevented by coastal defence works. Much can be learned by comparing physiographic and ecological processes at Orfordness with those at Dungeness, using Orfordness as an historical model for early Dungeness. This paper considers some of the evidence for these conclusions, examines the structures which survive to the present-day and discusses the ecological significance of the features, especially in terms of plant successional developments.     

The medicinal leech, Hirudo medicinalis (L.) (Hirudinea: Gnathobdellae), at Dungeness, Kent

WILKIN, P. J., 1989. The medicinal leech, Hirudo medicinalis (L.) (Hirudinea: Gnathobdellae), at Dungeness, Kent . An account of the ecology and conservation of the medicinal leech ( Hirudo medicinalis (L.)) at Dungeness, Kent, is presented.     

Isotopic (δ2Hf) evidence of “loop migration” and use of the Gulf of Maine Flyway by both western and eastern breeding populations of Blackpoll Warblers

Declining numbers of Blackpoll Warblers (Setophaga striata) have been documented at long‐term migration monitoring sites as well as in breeding areas. However, the “loop migration” of Blackpoll Warblers makes it difficult to ascribe population change at migration monitoring sites to specific breeding populations. Individuals from all populations across the breeding range of Blackpoll Warblers concentrate in fall along the Atlantic coastline of eastern North America prior to initiating a transoceanic flight to wintering areas. In spring, Blackpoll Warblers return along a different route, moving north into the southeastern United States where birds from eastern and western breeding populations then diverge during migration to reach their respective breeding areas. To monitor breeding populations outside of breeding areas and identify factors potentially affecting those populations, we must be able to identify where birds captured during migration breed and map seasonal variation in population‐specific flyways. To “map” population‐specific migration movements of Blackpoll Warblers, we used feather deuterium (δ²H_f) values and a spatially explicit model to assign molt origins of 289 Blackpoll Warblers moving through sites in the Gulf of Maine (GOM) region and at three locations further west and south (northern Great Lakes area, Pennsylvania, and Florida). The assignment method was validated with feather samples from 35 birds captured during the breeding season at Churchill, Manitoba, Canada. As predicted, the spatial pattern of movement within and between seasons reflected “loop migration.” Blackpoll Warblers captured during fall migration in the GOM region included birds from across their breeding range, whereas birds captured during the spring were exclusively from northeastern populations. During fall migration, Blackpoll Warblers captured at two sites west of the GOM were from breeding areas further northwest than those from western Canada that were captured in the GOM. Blackpoll Warblers captured in eastern Florida during spring migration were assigned exclusively to breeding areas in the northeast, suggesting that eastern and western populations diverge soon after entering the United States. Finally, most Blackpoll Warblers sampled at Manomet Bird Observatory originated from breeding populations in Alaska and western Canada that have shown a similar (70–90%) decline over the same period. Our results, therefore, not only document the “loop migration” pattern of Blackpoll Warblers, but, by mapping patterns of connectivity between breeding and non‐breeding areas, may help target conservation efforts for breeding populations of Blackpoll Warblers where most needed.     

Management plan for the Royal Society for the Protection of Birds reserve at Dungeness, Kent

THOMAS, G. J., GLOVER, J. & MAKEPEACE, P., 1989. Management plan for the Royal Society for the Protection of Birds reserve at Dungeness, Kent . A synopsis of a new management plan for RSPB Dungeness reserve is presented.     

Revised estimate of numbers of wintering Red-throated Divers Gavia stellata in Great Britain

Capsule An estimated 17 000 Red-throated Divers winter around Great Britain.

Aim To produce an up-to-date assessment of the numbers of Red-throated Divers wintering around Great Britain.

Methods A revised Great Britain (GB) wintering population estimate for Red-throated Divers was compiled using data primarily from systematic line transect surveys by aircraft over marine nearshore areas conducted during 2001–06, supplemented with county bird records and Wetland Bird Survey (WeBS) counts, both from 1995 to 2005. Population estimates for each survey area around GB were calculated as the mean of either annual means (aerial surveys) or annual maxima (WeBS, county bird records) of all data collected within January and February of each year. These were summed to give a revised GB wintering population estimate.

Results A total of 17116 (13198–21034, 95% confidence interval) Red-throated Divers were estimated to winter around GB. Distribution was uneven. By far the greatest numbers were found off southeast and east Britain (59.3% of the total was between Flamborough Head, Yorkshire, and Dungeness, Kent), with large concentrations off the English south coast (10.9%), north Wales and Liverpool Bay (9.8%), and eastern Scotland (6.1%).

Conclusion This is a minimum plausible population estimate and the true population size may be larger. The new 1% of population threshold for statutory conservation work is 170 birds.     

Fault bars and fluctuating asymmetry in birds: are the two measures correlated?

ABSTRACT.   As bio-indicators, bilateral asymmetry and fault bar formation have been found to be correlated with environmental quality, body condition, and individual fitness. Although commonly used as indices of the same parameters, it is not clear whether asymmetry and fault bars are equivalent measures of developmental history. We tested the possible relationship between these two metrics by measuring the degree of asymmetry and the number of fault bars in the wing and tail feathers of migrating White-throated Sparrows ( Zonotrichia albicollis ) at Long Point Bird Observatory on Lake Erie, Ontario, during October 2004. Within individuals, we found no relationship between the occurrence of fault bars and degree of bilateral asymmetry. In addition, individuals with higher fat scores had more symmetrical wings than individuals with lower scores, but did not have fewer fault bars. Together, these results suggest that fluctuating asymmetry and fault bar occurrence should not be used interchangeably as bio-indicators.