The Dowitchers - How to Tell Them Apart

                                Long-billed Dowitcher - Note: dark tail, no primary extension

The Dowitchers, how do we tell them apart?  This is a recurring dilemma for birders.  Both species occur here and they often get listed as ‘Dowitchers’ because they are not easy to tell apart.  This post is an attempt to make differentiating them a little easier.

The Short-billed (SBD) and the Long-billed Dowitchers (LBD) have very similar breeding and non-breeding plumages.  Both are of a similar size - SBDs are 28 cm long and LBDs are 29 cm.  They are part of the family, Scolopacidae.  They are medium-sized, stocky, long-billed shorebirds. They feed in muddy shallow water probing for aquatic insects and invertebrates in a rapid up-an-down sewing-machine-like fashion.  In flight they show a white wedge running from the middle of the back down to the barred grayish tail.  They usually feed and rest in flocks on tidal marshes, mudflats and bogs. 

                        Short-billed Dowitcher - Note: weak supercilium, primary extension

The SBD species is made up of three subspecies; Atlantic, Prairie, and Pacific.  Subspecies are not described for the LBD.  The Atlantic subspecies of the SBD is the one we are concerned with here.  It breeds in northern Canada from Labrador westward to the eastern shore of Hudson Bay.  The LBD is a more western species, breeding from northeastern Siberia eastward to the western and northern parts of Alaska and eastward to the Northwest Territories.  The SBD migrates in fall to the southern US and as far south as Brazil.  The LBD migrates in the fall to southern California and sometimes into northern South America.  Some move eastward in their fall migration and that is why we see some here on our coasts in the fall.  In fact, that is one clue in identifying this species.  A dowitcher seen here in late fall can quite likely be a LBD.  It would be very rare in the spring.  

                Short-billed Dowitcher  Note: streamlined body shape, light spotting, light barring

Differentiating these two species is difficult.  It apparently is easy in juveniles (which we don’t often see here), difficult with breeding adults and very difficult in winter plumage adults.  And add to that, the plumage can get worn or the bird may be moulting - which also makes it difficult.  So if you identify it as ‘dowitcher’, don’t feel upset.  You are not alone. Many go as ‘unidentified’ even by experts.

There are many differentiating features in these species.  These can help a lot but are not totally dependable.  They can vary among individuals.  For example, the LBD has a distinctive white supercilium which is more indistinct in the SBD.  However, you can have a flock of LBDs with an individual or two with indistinct supercilia.  The same goes for other traits.

The location in which you find these birds can help.  SBDs prefer coastal marine habitats especially muddy unvegetated mudflats next to shallow bays, lagoons, estuaries, salt marshes and sandy beaches.  LBDs prefer freshwater habitats especially those with short vegetation such as marshes, wet grassy meadows, flooded rice fields, agricultural flats, lakeshores and open mudflats.  

The appearance of the flock as they feed can be diagnostic.  LBDs are longer-legged.  They stand taller than SBDs and can feed in deeper water.  If you see a mixed flock in the same pool, the LBDs will show more space between their bellies and the water surface than the SBDs.  The body shape of the birds also is a good clue.  The SBD is much more streamlined and the LBD is rounder and more heavy-bodied looking.  

                Long-billed Dowitchers  Note: rounded body shape, prominent supercilium, long legs

The bill length, contrary to the names of these species, does not help in identification.  The LBD does have a slightly proportionately longer bill than the SBD.  But the bill lengths of the two species overlap.  In both species the female has a longer bill than the male.   But the bill length of a female SBD can equal the bill length of the male LBD.  The longest proportionate bill length is seen in the female LBD.  Given the above, the bill length is not a trustworthy identifying feature.  The tip of the bill of the dowitchers has tactile receptors enabling them to locate prey by touch while probing deep in the mud.  They feed on insect larvae, crustaceans, polychaetes, molluscs and plant material.

The call of these species is the best way to identify them.  This is not always heard but one must be listening carefully.  You might get only one chance to hear it!  The SBDs utter a soft, mellow ‘tu-tu-tu’ and the SBD flock is quiet while feeding.  The LBDs give a soft chatter while feeding and emit a high-pitched ‘keek’ when disturbed.  Hearing the sounds uttered by these feeding birds may be your only chance to identify them.

We need to look at two other features before we compare plumage.  The body shapes can help us tell them apart.  The SBD is more streamlined.  The LBD is more rounded with a rounded back and appears heavy-bellied.  So, looking at profiles can help.  Primary extension is also a clue, whether the primary wing feathers extend beyond the tail tip.  In the SBD the wing feathers extend beyond the tail.  This is not a long extension but it exists if the plumage is not worn.  It can change depending on the position of the bird.  If it is bent over (probing the mud, e.g.) the wing feathers are pulled a bit forward and the extension may not be as visible.  In the LBD the primary wing feathers do not extend beyond the tail feathers. 

Now let’s discuss plumage, an identifying feature which can help but can also be very difficult.  Complicating factors include feather wear, breeding or non-breeding plumage and moult. In the breeding plumage both species are patterned brown on the back and head with orange down the neck and breast.  In non-breeding plumage both species are grayish with the SBD lighter in colour than the LBD.  In the breeding plumage the SBD has dark speckles and barring on the sides of the neck, breast and flanks.  The LBD in breeding plumage has heavy spots on the sides of the neck and wedge-shaped bars down the flanks.  In non-breeding plumage both species are gray and the SBD is lighter in appearance with fine spotting and a whitish mottled breast.  In non-breeding plumage the LBD is darker in colour because it is more mottled above with a darker breast. The breast is a more uniform gray colour and the bird is less patterned on the back.

Long-billed Dowitchers  [Brian Stone Photo]  Note: non-breeding plumage, darker with mottled breast, white tips to scapular feathers on left bird, white distinct supercilium, dark loral stripe

In both plumages the supercilium is a key feature.  The LBD has a distinct white supercilium (line over the eye) and a dark loral stripe which continues past the eye.  The supercilium is less prominent in the SBD.  The scapular feathers can also be a clue.  In the SBD the pale tips to the scapular feathers connect to thicker pale edges running up the sides of the feathers.  In the LBD the scapulars are darker with well-defined white tips.  Like many other feathers used in identifying these species, these features are not always visible and can be variable.  

The tail feathers can also help.  Formerly I understood that the colour of the tail feathers was a good feature to differentiate the two species.  However,  recent texts don’t give much mention to this feature.  I was always taught that the SBD’s tail was black on white and the LBD tail was white on black, meaning that the SBD tail was mainly white and the LBD tail was mainly black.  The tail of the SBD is whiter due to wider white cross bars compared to the narrower black bars.  The SBD does not show any rufous or orange on its central tail feathers.  The tail of the LBD is darker, mainly black with narrow white or orange lines.  It can have rufous or orange in its central tail feathers.  That information is interesting and can be useful but it is difficult to see the tail of a dowitcher.  See the photo of the LBD below which clearly shows its black tail with orange lines. 

                Long-billed Dowitcher  Note: tail looks black with orange on feathers, bold supercilium

Acknowledging the variability of plumages, etc., in these two species and a careful study of the dowitchers especially with photos one should be able to differentiate many individuals.  Note also that even the experts have some they cannot tell apart.  With one in the hand it should be reasonably easy but we don’t get that chance often.

So, what are the key features to tell dowitchers apart in the field?  The CALL is the key feature.  We have to use our ears as well as our eyes!  Besides that, look at the SHAPE of the bird, the SIZE in comparison with the other dowitchers around it.  If it is in non-breeding plumage, is it darker or lighter?  If it is in breeding plumage, look at the spots and bars on the neck, breast and flanks.  The two species prefer different HABITATS:  the LBD prefers freshwater habitats and breeds in the far northwest; the SBD prefers saltwater habitats and breeds farther east, our Atlantic subspecies in Labrador and Hudson Bay.  The difficulty in separating the two species is exacerbated by the great variability in the SBD species.

Long-billed Dowitcher  [Jim Carroll Photo]  Note: non-breeding plumage, supercilium, dark loral line extending beyond eye, dark plumage with barring on flanks

I will conclude with a few interesting facts about dowitchers.  It has been shown that the SBD and the LBD diverged genetically more than 4 million years ago. For a long time both the SBD and the LBD were considered one species, the Long-billed Dowitcher.  The SBD was not separated from the LBD until 1950.  A nest of a SBD had been found and described in 1906 but nothing was made of it until much later.  The generic name of the species, Limnodromus, is from ancient Greek.  limne means ‘marsh’ and dromos means ‘racer’.  You can see how this fits.  The English name is from the Iroquois language and was first recorded in 1844.  The Long-billed Dowitcher was first described in 1832 by Thomas Say.  

The dowitchers are described as the ‘ideal bird’ for bird watching.  They are common here, are challenging for birders and allow us to approach for good viewing.  The male LBD courts the female by singing to her and then competes with other males by pursuing them in flight, displaying an aerial show of speed and agility.  We are not going to be able to see that in New Brunswick but it gives us something to think about. I can’t quite picture a singing dowitcher.

See the photo below.  What species do you think this is? Why?

Please note:  The dowitcher identifications in this blog post have been done by me and may be inaccurate.

Bird Populations Are Still Declining

 

Wood Duck, A Common Dabbling Duck  [B Schneider Photo]

The recent report from the Cornell Lab states that our bird populations are still declining, that some rare birds are on the verge of extinction and that some of our still-common species are rapidly declining.  These concerning data are ultimately related to human populations and human behaviour.  It is paramount that conservation action be commenced/increased immediately. The data for these revelations have been provided by many bird conservation groups in Canada and the US.  These include our own Christmas Bird Counts, Point Lepreau Sea Watch, Owl Nocturnal Surveys, Shorebird Surveys, etc.

A study in 2019 estimated a net loss of 3 billion birds in North America in the preceding 50 years.  Well, the sad news is that the decline is still happening even with the conservation efforts we have been making.  In 2019 the good news was that the duck populations had increased.  That is no longer the case; duck populations are now declining.

According to the data provided by Cornell Lab, here is the present state of our bird populations since 1970 (in %):

Ducks, dabbling and diving +24%

Waterbirds +16%

Ducks, sea  - 4%

Western forest birds  -11%

Eastern forest birds  - 27%

Shorebirds  - 33%

Aridland birds  - 41%

Grassland birds  - 43%

These data are chilling. We are well past the ‘Oh, well’ stage.  Much more  effective action must be taken. We cannot even pat ourselves on the back when talking about diving and dabbling ducks or waterbirds. The duck population has declined from about +45% in 2019 to +24% since 2019. The first thing we need to do about that is to lobby to stop duck hunting in New Brunswick.  This would only be one measure from many we need to do.  The increase in the last 50 years has been greatly influenced by the work done by Ducks Unlimited.  We need to give them more support and encouragement.

                            Greater Yellowlegs, A Common Shorebird  [Photo by B Schneider]

Look at our forest birds and our shorebirds!  What can we do about that? With forest birds the situation is complex. It is tied to clearcutting, aerial spraying and other forest management practices.  Loss of habitat and pollution of their environment are undoubtedly serious causes.  

                    Northern Parula, A Common Wood Warbler  [Photo by B Schneider]

There is a lot of good scientific work done on how to restore bird populations.  We need to be proactive.  Remaining in a reactive mode just doesn’t work anymore. We need to restore more wetlands, forests and grasslands.   Forest monocultures and cultivated grasslands are not conducive to healthy bird populations. We need to continue to develop forest, wetlands and grasslands that are protected from fire, flood, erosion and drought. 

According to Cornell, there are over 100 million birders in North America and in the US alone, they spend $279 million on their activities annually.  North American birders could have a lot of influence if we used much more of our time and resources on bird conservation and habitat restoration.

Let’s look at the history of bird decline. The largest number of bird species on earth occurred from the Miocene through the Pleistocene periods, about 20 million years ago. Since then the rate of extinction has exceeded the rate of population increase. In early times, before the advent of modern civilization, primitive man lived in harmony with bird populations and there was little population decline. 

With modernization, the extinctions accelerated.  The first species known to be eliminated by man was the Dodo (Raphus cucullatus).  The Dodo lived on the island of Mauritius in the Indian Ocean.  It was first discovered in 1507 by the Portuguese.  Man arrived by ship and slaughtered the birds and along with the rats, cats, pigs, and monkeys which they brought, they succeeded in killing all the Dodos.  Extinction date for that species was 1681. 

A similar event occurred in North America with the Great Auk.  It lived along the coast of North America from about Cape Cod northward and eastward to include Greenland and Iceland. Sailors and fisherman slaughtered the birds for meat and oil, took their eggs and feathers and used them for cod bait. That species was able to endure the onslaught until 1844 when it became extinct.

Other species that have become extinct in our modern times are the Passenger Pigeon, the Carolina Parakeet, the Labrador Duck, and the Heath Hen.  In fact since 1681, with the loss of the Dodo, 78 species and 49 accepted subspecies have become extinct in the world. Man was paramount in the loss of at least half of this number! We can add to that, with the number of species that are on the verge of extinction or have become extinct but are not officially classified as such: Eskimo Curlew, American Ivory-billed Woodpecker, etc.

It is only common sense to think that no species can exist forever and would have a normal life expectancy. Some scientists have calculated that number at 16,000 years. But that would depend on the birds changing environment and how well the species could adapt to new conditions. But the big problem we face is the surging human population and how difficult it is to convince humankind to change their behaviour.  It is often not even possible to halt the changing conditions even if the human population is working towards improvement. One thing is certain, humans need to become aggressive conservationists in our economy, our environmental work and in our future planning. Our world population in 2025 is estimated to be 8.2 billion and is projected to increase to 10 billion by the 2080s. The decline in bird populations will be even greater  in the future unless drastic measures are taken.

References:

Olin Sewall Pettingill, Jr. Ornithology in Laboratory and Field. Burgess Publishing Co. 1970.

Cornell Laboratory of Ornithology. 2025. eNews. New State of the Birds Report is a Clarion Call for Conservation Action.

Black Vulture, A Rare Winter Surprise

     The Black Vulture (Coragyps atratus) is not an avian species one would expect in New Brunswick in winter.  A Black Vulture was certainly not on anyone’s mind as a group from the Fredericton Nature Club took a field trip to the Fredericton Landfill site on a cold Sunday morning, 23 February 2025.                     

 About 22 people walked the long road up to the active dump site seeing many American Crows and Bald Eagles on the way.  We were pleased we had been granted special permission to be there and that this was a day no work was happening at the site.   It was obvious that we were approaching the active dump site because a large number of birds were on the ground and in the air.  It was, in fact, quite spectacular; crows, eagles, gulls in large numbers.  See the photo below.

                               Fredericton Landfill Showing Large Numbers of Birds [Justin Dutcher Photo]

The active site had birds everywhere; on adjacent mounds, on the road around the pit, in the pit and in the land sloping away.  There were Bald Eagles of all ages, gulls, and starlings just everywhere.  Some eagles stood atop the mounds like sentinels.  The rest were feeding on the debris or resting around the edges.  Gulls were feeding, flying and aggressively interacting with one another vying for better feeding sites.  There were so many starlings on the active site that they looked like pepper sprinkled over the area.  We did not realize just how many were there until they periodically took off in flight and then it looked like 1000s.  The gulls were very numerous and included mainly Herring Gulls and Great Black-backed Gulls.  It was fun to see so many  different ages of each species as they stood close to one another.  The plumage comparisons made good learning experiences.

There were some special gull species, too.  I saw 4 Iceland Gulls including one adult and 3 juveniles.  There was also at least one Lesser Black-backed Gull.   It was such a learning experience, for example, to have a Great Black-backed Gull and a Lesser Black-backed Gull adult standing close together and to compare the bills and colour of the mantles was wonderful for me.  

We were not long at the site when one birder excitedly pointed out an unusual large black bird standing on the edge of the pit just 20 metres in front of us - a BLACK VULTURE!  It seemed undisturbed by our presence and allowed ample time to study and photograph it before it flew away to edge of the area.  What was a Black Vulture doing in Fredericton in winter, or at all for that matter?

                                            Black Vulture at the Fredericton Landfill  [Photo by Bev Schneider]

The Black Vulture looked quite at home.  It was feeding and interacting with gulls in what looked like a normal fashion.  It was standing its ground with the aggressive gulls and seemed quite comfortable.  It would spend some time resting and some time feeding.  It made me wonder how long it had been here.  A few days or weeks perhaps?  See photo below showing the Black Vulture flying.  Note the white showing in the wing feathers.

                            Black Vulture Flying from Main Feeding Area at the Landfill  [Photo by Justin Dutcher]

I have seen many Black Vultures in southeastern US, mainly South Carolina.  There they associate with the Turkey Vultures.  Whenever they were on a large feeding site, a dead deer obviously killed on the road, for example, the Black Vultures would hold back and let the Turkey Vultures feed first and then move in a bit later.  The literature says that they let the Turkey Vultures open the killed animal and then move in to feed.  They did not seem pushy at all.  It was interesting to see a flock of Turkey Vultures feeding and the Black Vultures standing around or perched on poles or trees nearby waiting to feed.  When they did move in to feed both species would feed together.  

                                Black Vulture Feeding on an Opossum in South Carolina  [Photo by Bev Schneider]

The Black Vulture is a large bird, measuring 64 cm long and with a wing span of 145 cm.  It looks smaller than the Turkey Vulture because of its shorter tail but it actually is close to the same size.  It has glossy black feathers overall with a bare head and upper neck.  The skin there is a dark gray colour which is covered with wrinkles and nodules.  The bill is white or gray as are the legs and feet.  The inner primary feathers are white and this shows in flight but not usually when perched.  The wings are broad and it flies with several quick flaps followed by a flat-winged glide.  It likes to ride thermals, lifting it well up above the ground.  It is usually seen in flocks and often associates with Turkey Vultures.  It can be dominant over the Turkey Vultures and will sometimes drive them away from food.  

Black Vultures like open low land especially on coastal plains.  They roost and sometimes nest in trees.  The normal range is in the southeast of North America, from North Carolina to  Texas.  In Florida they are mainly seen on the mainland because they are hesitant to fly over water.  They also occur in southern Arizona and Mexico and south into the tropics.   Their range also extends over much of South America.  The range is expanding to the northeast as we have seen in recent years.

 Being a scavenger, this vulture mainly eats carrion.  Occasionally it will eat the eggs of other birds, turtles and lizards.  It will eat the young of other birds or small mammals and occasionally plant material.  As we have seen it will scavenge at garbage dumps.  

Black Vultures nest on the ground or up to 10 metres above.  In courtship the male will walk circles around the female with his neck extended while making a hissing sound.  They sometimes do courtship flights diving and chasing each other over the nest site.  The nest is usually located in a thicket or in a hollow log or in a cave.  It will sometimes go above the ground to build in a hollow tree or an abandoned building.  No actual nest is built but they may decorate its periphery with bright pieces of plastic, metal pieces like bottle caps or shards of glass. Two gray-green eggs with brown and lavender blotches are laid and incubated for 37-48 days by both adults.  Upon hatching the nestlings are covered with a buffy-coloured down.  Both adults feed regurgitated food to the young.  The young fledge at about 2 months of age.  They become fully flighted at about 75 to 80 days of age.  The juvenile birds have black bills and reduced bare skin area on their heads. 

The Black Vulture is usually silent.  When it does vocalize it is usually in grunts or hisses.  These usually occur when it is disturbed.  Like the Turkey Vulture it often stands with its wings outspread.  It is believed that this is to dry the wings and warm the body and to kill the bacteria accumulated on the feathers.  

 

                       Juvenile Black Vulture Showing Black Bill and Reduced Bare Area on Head  [Internet Photo]

The earliest report of a Black Vulture in New Brunswick was one in Campobello in 1879 and others occurred in the early 1900s.  They have appeared sporadically in the last 30 years.  The reports are of single birds.  One with a damaged eye was reported from Saint John from 1993-1995.  This bird (or another with an injured eye) has been seen also in Nova Scotia.  Most reports are of birds seen near the coast with a few from inland sites.  

So, our bird is unusual but not totally unheard of.  Never-the-less it was a great surprise to that lucky group of people who were at a large landfill site on a very cold Sunday morning!  It appears that sightings are becoming a bit more common.  For a species that is non-migratory one wonders why.  It may be because of loss of habitat in the south or a large increase in their population.  Sources say that the population is decreasing in the southeast so loss of habitat is likely.  The photos of ‘our’ bird show decreased bare skin on the head and upper neck making me wonder if ours is a young bird.  That might be expected in a wandering species member.  We wish that welcome visitor success and hope he stays here to expand its range permanently.  

A Winter Day of Birding and Musing About Low Hawk Numbers

 

                                                Rough-legged Hawk Light Morph

Boxing Day, December 26, 2024, dawned sunny and relatively warm, with a high of -3ºC.  We had been wanting a trip to Lower Jemseg for quite some time but kept delaying it because of pre-Christmas activities.  A free day, so this was the day!

The route to Jemseg and on down to Lower Jemseg makes a good birding ‘run’ this time of year.  I wanted to try to see some hawks and that is the place to go - or at least it used to be.  The last 2 or 3 years has changed things for this route and the hawk population in this area.  In years past we would see up to 20-plus hawks on that route on a good day.  I remember one day we saw 23 hawks.  If you add the Bald Eagles to that sum, you get a wonderful day of birding!  Well, not now.  For the last two years one is lucky to see 2 or 3 hawks and many times we see none.  

Our trip started with nothing and then in middle Sheffield, a fast stop for the first silhouette of a raptor in a tree.  An eagle, an adult Bald Eagle.  Our first raptor to record.  We then drove many kilometres without seeing any other large birds.  Two Common Crows were a welcome addition to our list.  We scanned hundreds and hundreds of naked hardwood trees.  These would have been adorned with beautifully coloured leaves just two months earlier.  Now we could see deep into the forested areas because of the openness.  The trees were adorned with snow, the remnants of the Christmas Eve storm.  

In Lower Sheffield we saw a huge flock of Snow Buntings.  Pulling over we got a good look at about 100 birds.  They would land on the road covering the shoulder and half of the pavement.  Quickly they would take flight and circle over the adjacent field, only to return to the road again.  Fortunately, they seemed to know how to avoid the traffic.  

The St. John River which runs alongside for most of the route was mostly frozen over.  There were only a few mid-stream open slivers of water, not really useful for waterfowl.  One of these open areas was close to shore and in it were 4 Canada Geese.  They were looking quite forlorn and obviously were the remnant of the much larger flock that was using the river as a staging and feeding area on their migration south.

Periodically we saw small flocks of finches feeding on turf and soil on the sides of the road where the plough has scraped the snow off.  The first few flocks we checked were of Dark-eyed Juncos, Black-capped Chickadees, and American Tree Sparrows.  As we got closer to Jemseg and onto the road to Lower Jemseg, these flocks became more frequent and were mainly Snow Buntings.  On the Lower Jemseg Road itself there was a late Savannah Sparrow feeding with the Snow Buntings.  

                                                                    Red-tailed Hawk

We arrived at the end of the road at the landing of the Jemseg/Gagetown summer ferry.  A good spot to let my small dog out for a run.  As we quietly stood there checking the rather large patch of open water for waterfowl, a hawk flew out of a large ash tree and sailed over our heads - a Rough-legged Hawk.  Wow!  I hadn’t seen a Rough-legged Hawk in 2 years.  I was very excited and watched admiringly as it soared over the big open field there.  It was a light morph bird.  We stood around checking further and found only a few more Snow Buntings.  Before we got back into the car the hawk returned to soar over again.   It must have known how happy we were to see that species today!

Our trip home revealed another species, a beautiful one.  As we left Turner’s Store in Jemseg a male Pileated Woodpecker flew across our view.  It seemed like a nice punctuation mark to our list.  The rest of our trip home did not reveal another raptor even though we scanned hundreds of hardwood trees.  When we arrived home in Douglas near Fredericton, we went for a short walk in a vacant hillside area and were blessed with another hawk flying across our path.  It landed in a tree overhanging the road giving me a chance to confirm its identity as a Red-tailed Hawk.  It then took off and as I moved up closer to where it had disappeared, there it was sitting in full sun high up in an oak tree and facing me, its breast brilliant in the bright sun.  The breast band and brown heard were easy identification features.

Winter is a wonderful time to bird.  Our landscape looks empty but it is surprising what can be found.  Other birds seen on this trip included Mourning Doves, European Starlings, Rock Pigeons and White-breasted Nuthatches.

                                                    Rough-legged Hawk Light Morph

What has happened to the former hawk population which wintered in the Sheffield/Jemseg area?  Serious birders have been pondering that question.  In Lower Jemseg this morning we stopped to talk to a retired biologist who was out on his morning walk.  When asked that question his reply was wise, “Well, it certainly is not just one cause but probably a multitude of causes all working together.”  He is probably right.  

Maugerville, Sheffield, Jemseg, and Lower Jemseg present good habitat for raptors.  Being a hardwood area over rich farmland, scrub and marsh, it provides rich feeding grounds.  The rodent population must have been high there in past years.  Much of the area floods each spring and I am not sure what damage that does to the rodent population.  I believe a certain percentage of rodents survive in their burrows during flood waters.  It is possible most of the rodent population dies out and is quickly replenished over the next year or two.  Surely this has something to do with the food supply for raptors.  In past years flooding did not seem to have an effect on the wintering raptor population.  So, what now is the cause of the decline? 

There has been a general decline in raptor populations over recent years.  For example, the Sharp-shinned Hawk population has declined by 47% at some count sites.  Generally speaking, causes of declines could include loss of habitat, scarcity of food resources, window strikes, predatory/prey cycles, effects of pesticides, and human disturbance.  What causes are affecting the raptor population in question?

                                                            Northern Harrier Female

With the Sheffield/Jemseg winter population we are concerned mainly with Red-tailed Hawks, Rough-legged Hawks, and Northern Harriers.  The global population of Red-tailed Hawks is estimated to be 2 million and considered stable.  In fact, in recent years their numbers have increased by 1.3% per year.  The Canadian population is estimated to be 500,000 to 1,000,000.  

The global population of Rough-legged Hawks is estimated to be 100,000 to 1,000,000.  Scientists claim this is difficult to estimated because their breeding grounds are so widespread and they have unpredictable migratory habits.  However, the population of Rough-legged Hawks has been stable since the 1970s.  The literature does say, however, that regional populations can fluctuate depending on the availability of prey and the weather in their breeding grounds.  The main threats to the Rough-legged Hawk population are habitat loss, vehicle collisions and shooting.  For example they suffer in some places from agricultural development on their wintering grounds.  Vehicle collisions would be more of a cause in their wintering areas.  The third important threat to their numbers is indiscriminate shooting.  It is illegal to shoot hawks in New Brunswick but our game laws are sometimes poorly enforced due to low numbers of enforcement officials.  

Breeding success is also a factor in hawk numbers.  Research tells us that the numbers of Rough-legged Hawks in the Arctic fluctuate with the size of the rodent populations there.  This is because Rough-legged Hawks are specialist predators of small mammals such as voles and lemmings.  If the prey species population numbers are high, hawks produce more young and raise them more successfully increasing their population numbers. 

Looking at the literature on the effects of flooding on small mammal species in the flood zone, one study from the Sacramento River found that after flooding all species declined dramatically and remained depressed for at least a year after flooding.  The voles were the first species to recover.  The only species that did not decline significantly were the arboreal species (squirrels).  The same study also found that the vole populations declined as agriculture sites became more mature.  

A study done in Albuquerque, NM, found that after annual flooding there was no clear effect of flooding on the density of small mammals.  They found that some mice used trees as refugia during the floods.  Another study found the highest numbers of small mammals on and near the non-flooded elevated parts of the area. Another study confirmed this and found that flooding was not detrimental to the rodent numbers.  Another study done at Dongting Lake in China where frequent flooding occurred found that there was a significant decrease in rodent populations after a long period of flooding compared to a short period.  They found that the rodent population increased rapidly after the flood and became greater than the unflooded areas in half a year.  

So what does this mean about the Sheffield/Jemseg site?  The winter population of Rough-legged Hawks is presently very low in this area.  This is not the case in other parts of New Brunswick.  A recent report from the Tantramar area reported 16 Rough-legged Hawks sighted in one day.  Are we looking at two different populations here?  One population might be migrating down the east coast and wintering at Tantramar.  Another population (now very low) might migrate down the St. John River to winter in the Sheffield/Jemseg area.  Perhaps some of this population has changed its route to the east coast.  Or perhaps the breeding success on the St. John River population was much lower than the east coast population. 

Has there been a change in habitat?  It does not appear that there has been significant changes in agriculture in the area.  It might be possible that a new/different agricultural chemical is being applied to the land.  There may be less acreage under cultivation.  This might make some of the former heavily populated rodent sites too mature and thus support a smaller population.  The number and duration of the floods might also play a part.  We seem to have fewer heavy floods now (speculation) so that might have an effect.  An argument against that is that the population seemed to be stable for many years and the floods probably fluctuated during that time with no appreciable change in hawk populations.  Or, no flood at all as happened in 2024?  One study mentioned above found that the populations became greater after flooding so perhaps no flooding is a detrimental effect.  And lastly, what about the breeding grounds?  If the population of rodents on the breeding grounds was low or the weather bad or the predator populations high, these factors could affect the breeding success.  

The biologist we discussed this issue with was right!  There must be many factors causing the decline in the wintering population of hawks in the Sheffield/Jemseg area.  We need more information.  A study of this problem might help us improve the  St. John River wintering hawk populations.