M
onitoring bird populations as they migrate past Long Point is
one of the most exciting and valuable programs run by the Observatory. Which bird species
have been increasing over time? Which species are decreasing and might be in trouble? LPBO
has been gathering data to answer these questions since its foundation in 1960. The
project has generated a unique and vast data set spanning nearly four decades — the
longest running program of its kind in North America.
Because of its geographic location, jutting out 32 km into Lake Erie, Long Point
attracts large numbers of birds during migration. Many tired birds, as they fly over Lake
Erie, head to Long Point as the nearest landing point, where they can rest and feed before
continuing on their journey. The resultant large concentrations of birds allow us to count
and monitor many species, as they migrate north in spring and south in fall. Counting
birds on migration is particularly valuable for monitoring populations of species that
breed in northern Canada, in areas that are inaccessible to more conventional monitoring
methods such as the Breeding Bird Survey.
We count birds at each of 3 field stations at Long
Point — one at the Tip, one about a third of the way out ("Breakwater"),
and one at the base of the point, (the Old Cut station which is open to visitors). These
stations are staffed by volunteers daily throughout the spring and fall migration. For
about the first 6 hours of each day, starting just before sunrise, volunteers capture
birds, band them, and then release them again to continue on their migration. Through
banding, we can learn not only the numbers of each species in the area, but what
proportion of them are young birds (an indication of breeding success), how healthy they
are (based on their weight and body fat), how long they stay at Long Point, and where they
are migrating to (based on birds that are later captured or found elsewhere and their
bands reported). Our migration studies result in many publications in the scientific
literature. In addition to the banding, volunteers also carry out a standardized
census to count birds that were not caught in our nets, and they keep track of all the
migrants they observe throughout the day. At the end of the day, all the participants
gather together and tally all the birds they recorded, to get an estimate of the total
number of each species that stopped at the station during the day.
The result is a huge data base. LPBO has been responsible for banding over 550,000
birds of about 270 species, more than any other non-government organization in the Western
Hemisphere. We have obtained over 500,000 daily counts of birds on migration at our 3 main
field stations. We have been actively developing methods to use these counts to monitor
population changes in bird species over time. These methods have been so successful that
they are increasingly being used by other stations throughout North America. By looking at
the average daily counts in each season, after some complex statistics (multiple
polynomial regression) to reduce variation due to weather and date, we are able to derive
annual population indices for each species.
From these indices, we can then look at long term population trends in many species.
The resultant pictures of bird populations are shown in the accompanying
graphs, which we invite you to browse.
A quick glance through these graphs suggests several patterns. One of the most striking
results is that many species appear to have undergone marked population fluctuations. For
example, many neotropical migrants (species that winter in the tropics) decreased in the
1960s, increased in the 1970s, and decreased again in the 1980s. Many temperate migrants
followed the opposite pattern. In the 1990s, many species have again been increasing,
though some species continue to decline.
Overall, especially in recent years, there have been a lot more species increasing than
decreasing. Although this does provide some grounds for optimism, there are some species
that still need our concern. Despite the fluctuations, some Canadian bird species have
shown fairly consistent declines over the years. This could be due to many factors such as
loss or deterioration of wintering habitats, or destruction and fragmentation of breeding
habitats.
Which species are declining? Some of the Neotropical migrants showing persistent
declines include most of the thrushes, Rose-breasted Grosbeak, and several warblers like
the Ovenbird, American Redstart and Canada Warbler. Declining species that winter in the
southern U.S. include the White-throated Sparrow, Rufous-sided Towhee and Brown
Thrasher.
We invite you to browse through the graphs to see for
yourselves what has been happening with other species. Please remember, when you are
interpreting the graphs, that they only represent a portion of the continent—most of
the birds we count probably breed in Ontario or western Quebec. For species that breed in
southern and central Ontario, where they are also counted by the Breeding Bird Survey
(BBS), we have found good correspondence in population trends between our estimates and
those from the BBS. However, population trends may differ elsewhere in Canada. To improve
our understanding of the continental bird picture, we are actively promoting development
of the Canadian Migration Monitoring Network, a chain of bird
observatories across the country using similar methods to LPBO to monitor bird
populations. We are looking forward with excitement to the time, in the not too distant
future, when we will be able to put together data from all of these stations to develop
composite maps of population trends across the country—data that will be invaluable
for guiding management and conservation activities to ensure that all of these birds can
be protected.
Readers interested in learning more about the results of our migration studies should
consult:
Francis, C.M. 1995. How useful are recoveries of North American passerines for
survival analyses? Journal of Apllied Sciences 22:567-577.
Dunn, E.H. and D.J.T. Hussell. 1995. Using migration counts to monitor landbird
populations: review and evaluation of current status. Pp. 43-48 In D.M. Power
(Ed.) Current Ornithology, Vol. 12. Plenum Press, N.Y.
Hussell, D.J.T. 1996. The influx of Black-capped Chickadees at Long Point,
Ontario in the spring of 1962: a 35-year perspective on an unusual event. Journal of Field
Ornithology 67:614-622.
Mundy, R.P. and J.D. McCracken. 1997. Bill color as an age character in Yellow
Warblers. North American Bird Bander 22:116-118.
Migration
Monitoring 