An experimental study of the Vulture species and competing raptor species of the Yavari River at the Lago Preto Conservation Concession, Peru

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An experimental study of the Vulture species and competing raptor species of the Yavari River at the Lago Preto Conservation Concession, Peru.

Photo of a turkey vulture by Elizabeth Stormfield

Elizabeth Stormfield

BSc Practical Research Project


Key words: Lago Preto, Vulture, Scavenger, Behaviour
A field study is conducted using bait in both open and closed habitats to ascertain which avian scavenger species are located in Lago Preto. Their behaviour at the bait platforms is noted and compared. The study compares the behaviour of the two main groups, Vultures and Caracaras and uses previous studies to expand on the data. Overall the methods are criticised and suggestions made for future study on a similar subject in the same area.


DICE, Dr R. Bodmer, The crew of the Clavero, Claudia, Rojer, Dr J. Groombridge.

Also, all of the students on the Clavero for making my time in Peru memorable especially Hazel Jackson and Nicholas Reynolds.

The Lago Preto conservation concession has saved a large portion (about 10.000 ha) of the Amazonian rain forest from destruction and logging. The student projects there have been a great help in monitoring the area’s biodiversity and management so far, but as yet there have been no studies into the scavenging species in that area. This is something that had been left behind in the need to monitor the endangered species in the area such as the Red Uakari. (25)
Scavengers such as vultures have a bad image in the eyes of some humans, mainly westerners, due to their association with death. They feed on fresh or decaying carcasses and so are associated with the death of the animal. This is odd as they do not kill animals for food. They became evolutionarily adapted to scavenging and so never developed the strong feet and long talons needed to bring down prey or the wings to chase them. Their beaks developed to rip and tear flesh and they lost their head feathers, allowing them to stay clean whilst digging in to their messy meals. Cultures that have lived along side these birds know these facts and so associate them with the souls of the dead. With their large soaring wings they become the messengers or ferry men of souls to heaven or the next life. (24)
Vultures have been associated with disease also and were thought to be one of the factors for the spread of anthrax and foot and mouth disease but it has been found that they do not. It is thought that they eat the carcasses before the disease can sporulate (anthrax). It is possible that the habit of urinating on their legs protects them from disease as the acid in their urine kills the bacteria they come into contact with. (1)
Vultures depend heavily on carrion for food and may gather in large groups at a food source as the next meal is never guaranteed. Direct physical competition over food is a daily part of their behaviour. Their large broad wings allow them to fly the long distances they need to find the carrion in their large home ranges. The new world vulture species are an example of parallel evolution. They are not related to other birds of prey but are more closely related to storks. They have evolved similar physical characteristics to the old world vultures to allow them to exploit the same ecological niche. (22)
The scavenging species of an area or ecosystem should be monitored as thoroughly as the rest of the species. Vultures integrate a large panorama of land and land-use and so a community of vultures must be a general indicator of the overall ecological heath of the area. By studying the vulture and scavenger communities over time it there may prove to be a change in the structure or number of vultures within the community which could be linked to ecological events. This information could then be used for future reference and may become a useful part of ecosystem surveys. Vultures can also be termed umbrella species as they are at the top of the food chain and their food source is varied and they require large portions of good habitat to survive. (21)
Species IUCN classification:
Greater Yellow Headed Vulture: Cathartes melambrotus is classified as “Least concern” with an estimated global population of 100,000 to 1,000,000 individuals. There is evidence of population decline but it is not yet serious enough to reach a higher designation (Near threatened). (2)
Turkey Vulture: Cathartes aura is classified as “Least concern” with an estimated global population of 4,500,000 individuals. (3)
American Black Vulture: Coragyps atratus is classified as “Least concern” with an estimated global population of 100,000 to 1,000,000 individuals. (4)
King Vulture: Sarcoramphus papa is classified as “Least concern” with an estimated global population of 10,000 to 100,000 individuals. There is evidence of population decline but it is not yet serious enough to reach a higher designation (Near threatened). (5)
Black Caracara: Daptrius ater is classified as “Least concern” with an estimated global population of 10,000 to 100,000 individuals. (6)
Yellow Headed Caracara: Milvago chimachima is classified as “Least concern” with an estimated global population of 1,000,000 to 100,000,000 individuals. (7)

Bird descriptions:

Fig 1. Black Caracara

Black caracara also known as the Yellow-throated caracara:

Daptrius ater


Often seen in family groups numbering between 3 to 5 individuals along riverbanks, exposed sandbars and perched high in the trees along forest borders. They eat a variety of food from carrion and nestlings to insects and palm fruit. They are truly opportunistic and will take what they can get. (8)

Fig 2. Yellow-Headed Caracara
Yellow Headed Caracara:

Milvago chimachima

40-46 cms

Small slim caracara with longish wings with a yellow-buff colour on head and body with dark brown wings and stripe, from eyes to back of the head, with a barred tail. More of a savannah and scrub bird but does share the habitat and similar habits to the Black caracara and so can often be seen along side it. (10)

Fig 3. Juvenile Yellow-Headed Caracara

Juvenile is darker with mottled markings but still with the dark stripe behind eyes. This bird can be difficult to distinguish at first. (10)

Fig 4. Greater Yellow-Headed Vulture

Greater yellow-headed vulture:

Cathartes melambrotus


This vulture has the usual bare neck and head but it is a wonderful rich shade of egg yolk yellow. The crown is sometimes tinged blue or red and the rest of its body is a deep black brown colour. The primary quills are white as in some other species of neo-tropical vulture and the wings are held nearly flat in flight over the top of the canopy. It is very solitary and will rarely gather in groups. It is very common in forested areas, greatly outnumbering the Turkey vulture. (8)

Fig 5. Black Vulture (American)

Black vulture:

Coragyps atratus


Only vulture likely to be seen at dawn and dusk (8)

The Black vulture, as its name would suggest, is black all over except for the end of its beak which is ivory and its legs which are tinted white by its own defecation. The primary quills are white again in this species and the vulture is the only one of the neo-tropical species to be seen at dawn and dusk. It will often roost and soar in groups and is highly gregarious. Hunts for its food using it’s vision and thus is more likely to be seen in clearings and on habitat edges.

Fig 6. Turkey Vulture (Resident species)

Turkey Vulture:

Cathartes aura ruficollis (the resident species) (9)


It is slim with long wings that are a very dark brown in colour with silver underneath (visible in wing displays and flight), a bright red head with ivory coloured bill. This is the resident species and as such has a white patch on the back of the head as shown in the photo above. Possibly another method of keeping cool as white reflects heat.

It is usually seen in groups although less in numbers than the Black vulture. Relies on its sense of smell to find food below the canopy and will soar high on the updrafts to catch the scent. Has been known to work co-operatively like the African species with a wide network of bird alerting the others to the presence of food. Unfortunately other vulture species also use this and follow too.

Fig 7. King Vulture

King Vulture:

Sarcoramphus papa


A true forest species with its bold colouring needed in the darkness with orange and red colours, blue white eyes and caruncled heavy bill make it a sigh worth seeing. It’s brightly coloured head and neck It is the largest of the species found at the Lago Preto site and dominant at feeding groups. It has a creamy white body and shoulders with the rest of its wings black. The wings are large and broad and it has a shortish square tail. (9) The juveniles get their adult colourings slowly and so can often be seen in the mid stage with black splotches on their white backs and duller head colours. (10)

Specific aims:

  1. What vulture species visit the Lago Preto Conservation Concession?

As a raptor study has not been carried out in this area before it would be interesting to see which species are using the habitat. Raptors are important parts of an ecosystem and as such should be studies alongside the other more charismatic species.

  1. Is there competition between the vulture species?

There have been other studies into the dominance hierarchies between vulture species amongst the African and other old world species and it would be exciting to see if such a hierarchy exists amongst the new world species.

  1. Is there competition from other scavenging raptor species?

Just as in the African savannah assemblages vultures have to fight off other species of bird and mammal alike (such as the hyena) it is possible that the new world vultures have to fight off other raptor species from their finds.

  1. What behaviour do all the scavenging raptor species exhibit?

Behavioural studies on the new world vultures are few and far between and so any addition to the archive would be beneficial, especially if the study is repeated as any unusual or new behaviour can be recorded and compared with this study.

  1. Which species were the first to arrive at a food source?

There is some discussion as to which species of vulture are the first to find a source of food and how these species find the food. It is known that the black vulture has no ability to smell and that they have to hunt by sight alone. Thus a comparison of the results from two types of habitat (open and closed) could be used to support or discount this idea.

  1. Do the species show different behaviour patterns in different habitats? I.e. closed verses open habitats.

As some species are more closely associated with the forest habitat, such as the king and greater yellow headed vultures, they might exhibit different behaviours in the two habitat types.

  1. Does proximity to humans affect their visitation or behaviour?

Are some species of vulture more shy or timid around humans and are some more brazen? There are reports of Black vultures being a problem around rubbish dumps and airports so these bold behaviours may be exhibited by the black vulture and/or possibly another species.

  1. Does weather have an effect on their behaviour patterns?

As the vultures depend on the rising thermals to soar higher to search for food it is possible that weather could affect their abilities to use these and could limit the numbers seen or in fact the behaviour seen during a weather change. Also weather such as rain may cause the birds to shelter as damp feathers are not conducive to flying.

  1. Does time of day have an effect on their behaviour patterns?

Some species of bird are more active at certain times of day and so it is possible that the vulture species are also active at different times of day such as the black vulture which is the only vulture to be seen at dawn and dusk, possibly due to it’s smaller size and lighter weight allowing it to be more active before the thermals have the uplift the heavier vultures need to travel.

Study site:

Fig 8. Green square indicates the location of the Lago Preto Conservation Concession, Dr Rick Bodmer. (12)

The Lago Preto Conservation Concession is an area covering 10,000 hectares of some of the most diverse tropical forest in the western Amazon. Sited on the Peruvian side of the white water Yavari River that divides Peru and Brazil it contains 3 distinct habitat types.

  1. Varzea; a seasonally flooded forest (4-6 months of the year).

  2. Aguajal; Palm swamps dominated by the emergent mauritia palm which provides fruit for a wide variety of forest species.

  3. Terra Firma; upland forest with a high canopy with emergent trees reaching up to 30 metres.

My river study sites 1, 2 and 3 were located along the exposed river bank (consisting mainly of clay type soil) and the forest sites 1, 2 and 3 within the Varzea. (13) The study was conducted from the boat The Clavero which was docked on the Yavari River.

Fig 9. The Clavero, home and observation platform for the duration of the study.

River sites:

These were platforms cut into the clay banks of the river that had been exposed by the receding water levels. I had initially wanted to get prints from the platforms so that the scavenging species that visited after I stopped observations could be recorded but the type of soil was not right for that kind of study. Thus they were just flattened into an area about 1m by 0.7m and the surrounding or covering vegetation cut back a little to allow a good view point from the observation deck of the boat. The first platform (River Site 1) was about 10m from the back of the boat along the river bank and the second platform (River Site 2) was 10m further along (20m in total). The idea was to see if the knowledge of human activity in an area close to the food source would cause them to stay away or display different behaviour than at a food source further away.

The third platform was made when the receding waters of the river made it necessary to move the boat as it was becoming stuck. This left the first platform unusable as the boat was right next to it. I constructed another platform where the boat had been. His allowed me to see if the birds were just arriving at a site because they had found food there before or if they were actively finding it themselves.
Forest sites:

To compare the speed at which the birds found the food and the different behaviours exhibited in closed habitats I experimented with forest sites.

The first (Forest site 1) was in the forest next to Huapo lakes on the right side of a path leading to the Aguajal. The leaves were cleared from an area the same size as the river platforms (1m by 0.7m) and observations were made from about 20m away. The site was relatively open with not very densely packed trees and flat ground with little to no ground vegetation. This allowed a good view of the site with the naked eye and binoculars.

The second site (Forest site 2) was about 10m before the Lago Preto Lake and as before to the right side of the path into the forest. The distance from the platform area was a lot less but a hide of sorts had been constructed for observations.

The third forest site (Forest site 3) was the same place as the second forest site but the hide had been dismantled and a new one placed twice the distance away.
Data Collected:

  • The Time

  • The weather graded on a scale from 1-5 with 5 being the most extreme. The categories for weather were:

  • Heat

  • Cloud cover

  • Rain

  • Wind

  • Humidity

  • The species seen

  • Whether the birds were adult, sub adult or juvenile

  • Which platform they were at

  • Behaviour in code form from the ethogram below

Each observation period was started as soon as possible after the bait was put out which in the case of the river sites was about 5 minutes after the bait was laid, in the forest it was as soon as the bait ha been laid due to the proximity of the hide. Observation periods were either in the morning or afternoon with only one day having both (observation periods 6 and 7) which was due to the large amount of fish used that day.

The start times for the morning and afternoon periods differ from day to day but are usually around 8-9:30 am for mornings and 1-2pm for afternoons with one evening period started at 4:30pm. The differing start times were mainly due to the availability of a guide to help with the set up and baiting of the platforms and the availability of fish. The evening period was mainly to see if there was a specific time that the birds would stop feeding and leave to roost, which birds were still around and active in the evening and whether the evening watches were feasible due to the low light.
The weather was recorded using a scale of 1-5 with 5 being the most extreme, i.e. very heavy rain would be noted as 5 where a small shower may be written as 2 or 3, drizzle would be 1. This way I was able to note any changes in behaviour that may have occurred from the change in weather.

Species name

Adult code

Juvenile code

Black caracara


Yellow-headed caracara



Black vulture


Turkey vulture


Greater yellow-headed vulture


King Vulture



Unidentifiable Vulture species


Indistinguishable bird of prey


The table above shows the codes that I have used to distinguish between the species during the field study and within the data. Using these codes made it much easier to get all the information down and took up much less space.

As can be seen from the table above there was some variation in the freshness of the fish over the observation periods. There was also a day where there was no fish and as such I was just observing the birds that were around the site. Interestingly it was this observation period that saw the most interesting behaviour from the Yellow headed caracara, a fight between an adult and a juvenile resulted in a spectacular display. Both birds flew into the air and started chasing and attacking each other in the air, resulting in the birds locking talons and spinning down through the air till they let go almost too late. It was amazing to watch and could have been a territory dispute as there were some Black caracara’s involved also and they share the same habitat along the river edge.

Observation period


Platform 1

Platform 2

Platform 3




Fish: Sardines fresh



Fish: Catfish and Sardines

Plastic bags of fish guts on poles over platforms 1 and 2



Fish: Catfish and Forsaca

What was left in the bags of fish guts.



Fish: catfish

No bags of fish guts



No Fish



Comparison Fresh and rotten fish, Platform 1 rotten and Platform 2 fresh



Fish: Catfish day old



Fish: Catfish, 3 days old kept out in the sun in a black plastic bag



Fish: Catfish very fresh



Fish: Catfish day old



Fish: Catfish day old



Fish: Catfish day old



Fish: Catfish day old



Fish: Catfish day old



Fish: Catfish day old

The main fish that was used was catfish as they would be swimming around the boat due to the scraps that were thrown overboard. They were not fit for human consumption and so they were caught for the vultures. Each platform would be baited with on average half a bucket of fish which would be chopped into chunks about 2 by 3 inches. This was to stop the birds leaving the site with a whole fish and ending the observation periods quicker.

An ethogram was drawn up from the basic behaviours I expected to see in the vultures and was added to as and when new behaviours were noted. This allowed me to note my observations down much faster and more accurately than describing everything. This also meant that the 5 minute scans were much more accurate as I took less time to write and therefore got more of an instantaneous snapshot of the bird’s behaviours.
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