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Wildlife Populations

> Migratory double breeding of five North American songbirds

For the first time, biologists have documented a second breeding season for five species of North American songbirds as they head south towards their wintering habitat in Central and South America. After initially breeding in temperate regions of Canada and the United States, the birds stop over in western Mexico and breed again, having implications for conservation planning.

This is the first time that biologists have recorded “migratory double breeding” for New World birds, and the first instance of southbound double breeding in the world. Some Old World species have been known to double breed, but do so as they move north in the spring.

It has been long known that yellow-billed cuckoo, yellow-breasted chat, orchard oriole, Cassin’s vireo and hooded oriole travel to northwest Mexico following breeding in the north to molt and make use of the seasonal monsoonal rains in the area. Now, a subpopulation of these species clearly breeds again in Mexico before moving further south to winter.

These results give evidence that breeding populations of these five species are potentially subsidized by areas outside their suspected American and Canadian breeding range, and in areas of northwestern Mexico that are currently undergoing large-scale agricultural development.  

Researchers say the conversion of coastal thorn forests to industrial agriculture could be responsible for population declines in migratory double breeders and in the populations of molting birds that also use the region as a stop over.

For example, the yellow-billed cuckoo could be particularly susceptible to landscape changes in western Mexico because it may require the second breeding season to keep the species viable. The bird has almost disappeared from most of its breeding range in the United States and Canada, and its overall population size is down.

This study challenges the long-held assumption that birds are too limited by natural hormonal and reproductive systems to add additional stages of life history into their annual cycle.

Using stable isotope methods to predict the approximate latitude where tissues were formed, researchers from the University of Washington and Environment Canada investigated feathers, muscle, and reproductive tissues of birds breeding and molting in late summer in western Mexico. It was shown that some birds were local residents, others moved to this area to molt after breeding in western North America, and another distinct group of birds initiated breeding there clearly after an earlier attempt in Canada or the United States.

This research underlines the need to establish migratory connectivity for populations of migratory birds currently protected by the Migratory Birds Convention Act. Researchers urge programs and policy to consider connectivity in general and migratory double breeding in particular when developing demographic models, population studies, and conservation plans.

Source: Rohwer, S., K.A. Hobson and V. Rohwer. 2009. Migratory double breeding in neotropical migrant birds. Proceedings of the National Academy of Science 106: 19050-19055.

Contact: Keith Hobson (306) 975-4102

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> Human activity linked to bird evolution

Ecological changes resulting from human activities are strong enough to initiate a quick evolution in birds, according to a recent study.

A single population of European blackcaps, a small migratory songbird breeding in Germany, has split into two genetically different groups within just 30 generations because human activities, like bird feeding, have created suitable conditions for one population to migrate a lesser distance and feed on different food. Isotopic tools developed at Environment Canada allowed the two populations to be identified on their common breeding grounds.

Seeds and fat provided during winter at backyard bird feeders in the United Kingdom, together with milder winters over the last forty years, helped establish a north-western migration route that is 550 km shorter than that of the population that migrates to the south-west to Spain and feeds largely on fruit.

These changes in food resources have resulted in differing beak morphology, with the UK-wintering population having relatively narrower and longer beaks than the Spanish population, a trait adaptive to feeding behaviour at bird feeders. The UK-wintering birds are now browner and have more rounded wings, which are more manoeuvrable but less adapted to long-distance flight.

Since these birds share the same breeding range, where genetic mixing is possible, the study has scientists discussing how reproductive isolating mechanisms must have evolved to stop the birds from interbreeding.

The UK birds return in the spring to Germany ahead of the Spanish wintering birds, initially providing a means of separating breeding between the two groups. However, it was found that UK-wintering females arrive at the same time as Spanish-wintering males. The researchers suspect that the physical and genetic changes between the two groups may be preventing the birds from interbreeding.

Evolution, as manifested by the measurable genetic and physical differences between these two groups, is normally a slow process but has occurred here within a human lifetime. The researchers suspect that similar adaptations could have occurred in 50 bird species that have recently changed their migratory behaviour. Species that disperse to different wintering habitats are more likely to have experienced this type of evolutionary change, since adaptations to differing wintering conditions are more likely, say researchers.

This study shows the immense impact that human activities can have on the evolution of wildlife, and flags the issue for managers who need to consider migratory populations in terms of management groups. The linkage among breeding, wintering and migratory stopover sites (migratory connectivity) needs to be established to better inform management and conservation decisions. Fortunately, isotopic tools developed at Environment Canada now allow for the investigation of such connectivity at continental scales.

Source: Rolshausen, G., G. Segelbacher, K.A. Hobson and M. Schaefer. 2009. Contemporary evolution of reproductive isolation and phenotypic divergence in sympatry along a migratory divide. Current Biology 19: 1-5. Published online.

Contact: Keith Hobson (306) 975-4102

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> Seabird population and ecology changes since 1970

A recent review of seabird monitoring results, led by Environment Canada, assessed trends in seabird populations and environmental change in Canadian marine ecosystems over the past 30 years.

At six oceanographic regions, researchers examined seabird populations, diet, timing of breeding, egg and clutch size, colony attendance, and geographic distribution in order to draw broader conclusions about large-scale and persistent ecosystem change over time. They found that population and breeding biology indicators were generally similar within marine regions, but differed markedly between regions.

Monitoring at Triangle Island on the Pacific coast saw significant changes in diet, timing of breeding, adult survival and reproductive success for some species. These changes have been attributed to changes in sea surface temperature and the timing and intensity of upwelling, which affects the availability of prey species within the colony range. In contrast, areas further north, including Haida Gwaii (Queen Charlotte Islands) saw an increase in numbers of burrow-nesting auks, including ancient murrelets and rhinoceros auklets, suggesting that ecological factors remain suitable. However, Cassin’s auklets showed small declines.

Several seabird species in the eastern high Arctic experienced changes in breeding, reproductive success, and adult colony attendance since 1975 in response to variation in ice condition. While some species, like black-legged kittiwakes experienced positive population trends, others showed signs of decline, with ivory gulls declining by 80 per cent. Glaucous gull numbers in both the high and low Arctic declined by 50 per cent. In Hudson Bay, the very abundant thick-billed murre has not adjusted its timing of breeding to match the earlier sea ice break-up, leading to negative impacts on several reproductive indices. These changes coincide with changes in diet and indicate a substantial change in marine food webs in response to earlier sea ice break-up related to climate change.

A cold water event off the coast of Newfoundland and Labrador in the early 1990s affected the availability of prey, and subsequent years showed a population decrease in some species of gull and auk after years of increasing population sizes. However, overall, auk populations are stable in this zone. Reductions in gill-netting have likely benefited the diving birds.

Conditions for seabird reproduction in the Atlantic Maritime region were good until 2003, when numbers dropped dramatically and a major tern colony was abandoned. This change was associated with the disappearance of herring from their diet and increased predation by gulls.

The study concluded that good information on major oceanic events can be obtained by intensively monitoring a small suite of seabird colonies, spread over different marine ecozones. An approach that studies several species and combines population, diet, and reproductive monitoring gives the best hope of understanding underlying mechanisms.

Source: Gaston, A.J., D.F. Bertram, A.W. Boyne, J.W. Chardine, G. Davoren, A.W. Diamond, A. Hedd, W.A. Montevecchi, J.M. Hipfner, M.J.F. Lemon, M.L. Mallory, J.-F. Rail and G.J. Robertson. 2009. Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs. NRC Research Press Environmental Reviews 17. Published online.

Contact: Dr. Tony Gaston (613) 998-9662

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Habitats and Ecosystems

> Assessing ecosystem recovery after removing a source of pollution

Some Arctic marine ecosystems can naturally recover from chronic pollution more efficiently than previously thought, according to a research paper that highlights ecosystem recovery in Saglek Bay, Labrador.

The extent and concentration of polychlorinated biphenyls (PCBs) decreased significantly in the marine sediment, fish, and seabirds of Saglek Bay just eight years after removing the source of the PCB pollution.

This study, led by researchers from the Nunatsiavut Government, Royal Military College of Canada and Neil Burgess of Environment Canada, is one of the first that evaluates the recovery of this type of ecosystem after removing PCB-contaminated soil from Saglek beach. The PCB clean-up was done in the late 1990s for the Department of National Defence.

The research team found that, in only eight years, PCB concentrations in surface sediment decreased an average of 10 times, concentrations in black guillemot decreased an average of 6 times, and in shorthead sculpin 19 times. The comparable decreases in sediment and indicator species suggests that natural ecosystem recovery following contaminant removal is occurring faster at Saglek Bay than commonly observed at other contaminated marine sites.

This study lends weight to the utility of using black guillemot and shorthead sculpin as indicator species to monitor Arctic marine ecosystem recovery, as they appear to accurately reflect changes in contaminant levels in the local marine food web.

This collaborative study was supported by the Department of National Defence, Environment Canada, Fisheries and Oceans Canada, the Nunatsiavut Government and Parks Canada.

Community consultation on these and additional findings will take place in the spring of 2010.

Source: Brown, T.M., T.A. Sheldon, N.M. Burgess and K.J. Reimer. 2009. Reduction of PCB contamination in an arctic coastal environment: a first step in assessing ecosystem recovery after the removal of a point source. Environmental Science & Technology 43(20): 7635-7642.

Contact: Neil Burgess: (709) 772-4143

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> Alpine birds adjust life history strategy to survive in harsh and variable conditions: Live low and fast, or high and long!

To make up for shorter breeding seasons in cold, challenging mountain habitats, some high elevation songbirds invest more energy in living longer and improving offspring survival ('slow lifestyle'), than their lower elevation counterparts (‘fast lifestyle'). Although 'slow lifestyles' can result in fewer offspring produced at high altitudes, these offspring have longer lives and have more time to breed in their lifetime.

Considerable variation can exist between species, but horned larks, savannah sparrows and dark-eyed juncos produce fewer offspring each year, but have higher juvenile and adult survival rates at higher altitudes than the same species at lower altitudes, according to several recent studies from Environment Canada and the University of British Columbia.

These three songbirds appear capable of coping with current conditions, but as mountain environments and northern latitudes experience more change due to climate warming, it is unknown how these species will be able to cope with more extreme future conditions.

The pattern between survival and reproduction seen in songbirds at high elevation is not consistent with all bird communities, and can be influenced by climate, temperature, predators and food availability. A recent study in the Yukon found that white-tailed ptarmigan had 25 per cent more offspring than rock ptarmigan, but rock ptarmigan were found to live 25 per cent longer than white-tailed ptarmigan. At the same location, these closely related species responded very differently to unfavourable spring conditions, with the ‘slow lifestyle’ rock ptarmigan suffering greater reductions in reproduction than the ‘faster lifestyle’ white-tailed ptarmigan.

These trade-offs between reproduction and survival have strong implications for predicting how species will respond to greater environmental changes associated with climate change.

Source: Bears, H., K. Martin and G.C. White. 2009. Breeding in high-elevation habitat results in shift to slower life-history strategy within a single species. Journal of Animal Ecology 78(2): 365-375.

Source: Camfield, A.F., S.F. Pearson and K. Martin. 2010. Life history variation between high and low elevation subspecies of horned larks. Journal of Avian Biology. In press.

Source: Camfield, A.F. and K. Martin.  2009. The influence of ambient temperature on horned lark incubation behaviour in an alpine environment. Behaviour 146: 1615-1633. 

Source: Martin, K. and K.L. Wiebe. 2004. Coping mechanisms of alpine and arctic birds: extreme weather and limitations to reproductive resilience. Integrative and Comparative Biology 44: 177-185.

Source: Martin, M., A.F. Camfield and K. Martin. 2009. Demography of an alpine population of savannah sparrows. Journal of Field Ornithology 80(3): 253-264.

Source: Wilson, S. and K. Martin. 2010. Variable reproductive effort for two sympatric ptarmigan in response to spring weather conditions in a northern alpine ecosystem. Journal of Avian Biology. In press.

Source: Davidson, P., S. Wilson, H. Bears, A.F. Camfield and K. Martin. 2007. Birds in high places. BirdWatch Canada 41: 4-7.

Contact: Dr. Kathy Martin (604) 940-4667

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Health Effects of Toxics

> Second generation anticoagulant rodenticides found in three species of owl in Western Canada

Researchers say owls are at some risk from rodenticides after a recent study found common rodent poison in the livers of 70 per cent of sampled owls across British Columbia and the Yukon, with 15 per cent having concentrations high enough to reportedly cause mortality.

Although rodenticides were directly responsible for death in only three per cent of the sample, researchers suspect that second generation anticoagulant rodenticides (SGARs), like brodifacoum and bromadiolone, are likely contributing to more deaths than can be detected through post mortem observations and liver residues.

Environment Canada researchers collected 164 dead barred owls, barn owls, and great horned owls from 1988 to 2003 from many partner organizations in British Columbia and the Yukon. Although most owls died due to trauma (electrocution, attacks by other wildlife, and motor vehicle or window collisions), the high presence of SGAR residues made it difficult to rule out that owls may have experienced behavioural changes due to rodenticide exposure, leaving them more susceptible to accidents.

In British Columbia, from 1991 to 2003, sales of the active ingredient in brodifacoum and bromadiolone increased 100 per cent and 24 per cent, respectively. These chemicals are found to be more acutely toxic than the so-called first generation rodenticides, and tend to persist longer in animal tissues. SGARs can be purchased without a license to help control pests in and around commercial and residential establishments, food service, garbage dumps, and transportation facilities.

As a result of evidence from studies such as this, regulations in Canada and the U.S. have recently required amendments to labels on all products containing brodifacoum to reduce poisonings of non-target wildlife. Research and monitoring efforts continue to identify the effects of rodenticide, particularly on vulnerable owl populations, and to develop new tools to measure the effects of non-lethal exposures.

Environment Canada scientists began to suspect anticoagulant rodenticides in poisonings of birds displaying severe abdominal haemorrhage during their study on anti-cholinesterase pesticides and their poisoning effects on raptors. Research on anti-cholinesterase pesticides has led to the local withdrawal of harmful chemicals because of their poisoning effects on non-target wildlife.

Source: Albert, C.A., L.K. Wilson, P. Mineau, S. Trudeau and J.E. Elliott. 2009. Anticoagulant rodenticides in three owl species from Western Canada, 1988-2003. Archives of Environmental Contamination and Toxicology 58(2): 451-459.

Contact: John Elliott (604) 940-4680

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