Study

Cutting of Mauritia flexuosa palms to provide nest cavities for blue-and-yellow macaws Ara ararauna at Tambopata National Reserve, Madre de Dios, Peru

  • Published source details Brightsmith D. & Bravo A. (2006) Ecology and management of nesting blue-and-yellow macaws (Ara ararauna) in Mauritia palm swamps. Biodiversity and Conservation, 15, 4271-4287

Summary

Blue-and-yellow macaws Ara ararauna occur in lowland forest, savannah and gallery woodland in Central and South America. They are still common in remote and protected areas, but are declining near human habitation due to habitat loss and collection for the pet trade. Like most large macaws, they have a low reproductive rate and reproduction may be limited by a lack of nest sites. Mauritia flexuosa palms provide important nest sites for macaws and several other parrot species. This large palm usually grows in swampy areas often in dense, almost monospecific, stands. The palm fruits are an important food source for many animals, including macaws, and are also colleted and eaten by people.

A study showed that artificially decapitated Mauritia palms attract nesting blue-and-yellow macaws which in turn could be viewed by 'ecotourists' and an income generated through charging fees to view and photograph them. In the study described here, a small section of palm swamp was managed to encourage macaw nesting by cutting the tops off of palms and clearing the understory vegetation.

Study site: Blue-and-yellow macaw Ara ararauna were studied in four areas of Mauritia flexuosa palm swamp in the department of Madre de Dios, southeastern Peru between November 1999 and March 2004.

Two swamp areas (with a dense closed canopy almost entirely of Mauritia palms) were in the 537,000 ha Bahuaja Sonene National Park (BSNP) (250 m altitude). One area comprised healthy swamp, ('healthy BSNP swamp') and the second a dieing 3 ha section of the same swamp where a small stream was filling the area with sand and gravel and slowly killing the palms ('dieing BSNP swamp').

A further two areas were within a 13 ha swamp adjacent to Tambopata Research Center (TRC) in the 275,000 ha Tambopata National Reserve (250 m altitude). The canopy of this swamp is dominated by Mauritia, but also with small numbers of Euterpes precatoria, Hura crepitans and other tree species. This site was divided into a 'healthy TRC swamp,' and a <1 ha section where the understory vegetation was cleared and the tops of 42 palms removed between 1992 and 1999 ('managed TRC swamp'). All four study sites were within 16 km of each other and near a large clay lick where many blue-and-yellow macaw were present daily.

Nest monitoring: Nests in the dieing BSNP swamp were found, observed and measured over 4 days in February 2002. Trees were considered nests if chicks called from inside, adults remained inside throughout the day or adults entered in the early morning. Observations at TRC showed that at this time of the year most blue-and-yellow macaws had chicks or had abandoned the nest sites for the season, indicating that trees occupied at this time were almost certainly nests. Nests in the healthy TRC swamp were discovered opportunistically and observed for activity approximately once every 7–10 days through the nesting season. Nests in the managed TRC swamp were observed (and sometimes inspected by climbing) through the breeding seasons from 1999 to 2004.

Nest measurement: Palm DBH was measured and height estimated using a clinometer. In March 2000, the depths of the central cavities of the cut palms in the managed TRC swamp were measured by lowering a weighted tape measure into the cavity, and whether the cavity was filled with water was recorded. In March 2001, the cavity depth of the six trees cut in 1999 was re-measured.

Palm swamp management: The habitat management aimed to create a nesting colony of macaws in a stand of tall, isolated, dead palms surrounded by low vegetation, similar to that of the dieing BSNP swamp. In an attempt to achieve this, understory vegetation was cleared and the tops cut from 41 palms in a small section of the TRC swamp. Palms were cut during the dry season (April-September) in 1992 (n=10), 1993 (n=13), 1995 (n=11) and 1999 (n=6). In 1992 and 1993, the managed area was about 30 m in diameter. In 1995 and 1999, the original area was left to regenerate and cutting was undertaken in a 40 m diameter area 10 m from the first site.

Palm swamp structure: Live palms were taller in the healthy BSNP swamp than in the dieing BSNP swamp or the healthy TRC swamp. The DBH of live palms was also greater in the healthy swamps. The density of live trunked palms in the healthy BSNP swamp (545 ±85/ha) was significantly greater than in either the healthy TRC swamp or dieing BSNP swamp. In the dieing BSNP, the live trees had very small crowns resulting in a very open canopy. Dead palms were rare in both healthy swamps (<25/ha), but abundant in the dieing BSNP swamp (263±70/ha). The densities of juvenile palms differed among sites, seedlings densities being lower in the dieing BSNP swamp but only marginally so.

Natural macaw nests: In total, 28 blue-and-yellow macaw nests were found in the study areas, all in dead Mauritia palms. These palms were isolated from other tall trees and overhanging vegetation. The macaw nests in the healthy TRC swamp were in outstandingly tall dead palms that rose above the lower more broken canopy. These palms also had greater DBH and height than unused dead and live palms in the area. Nests were never found in shorter dead palms below the main canopy. The choice of isolated trees with deep cavities is presumably an anti-predation strategy.

Twenty-five nests were found in the dieing BSNP swamp. All were also in palms isolated from surrounding vegetation. Here birds did not have to choose the tallest palms, as nearly all rose well above the <2 m tall herbaceous understory. The height and DBH of used and unused dead palms and live palms in the adjacent healthy BSNP swamp did not differ significantly. Large numbers of red-bellied macaw Orthopsittaca manilata were also present in the dieing BSNP swamp and were presumably nesting.

Palm dynamics in managed areas: Cutting Mauritia palms exposed the soft inner cortex which slowly rotted away leaving an outher vertical tube of hardened bark-like material. Nine months after cutting, the average cavity depth was 19 ±35 cm (range 0–89 cm, n=6). By 21 months these cavities averaged 76±82 cm (range 5–210 cm). Four years after cutting, a different group of palms had cavities averaging 552±223 cm deep (range 258–752 cm, n=4). The palms began to fall 4 years after cutting. Seven years after cutting all had fallen (n=34). In areas cut in 1992 and 1993, seedling and juvenile densities 8 years later were 3,060/ha and 1,940/ha, respectively. A trend towards higher seedling and juvenile densities in healthy TRC swamp may be due to the more broken canopy allowing more light penetration.

Macaw nests in managed areas: From 1990 to 2003, 12 blue-and-yellow macaw nesting attempts in cut palms in the managed TRC swamp were monitored. The number of available dead palms and the number of chicks fledged per palm declined steadily throughout the course of the study: from 12 palms and 0.25 chicks fledged per palm in 2000 to 5 palms and 0 fledged in 2004. Clutch size averaged 2.6±0.53 eggs (range 2–3, n=7 clutches). The palms used for nesting had deeper cavities and had slightly greater diameters than those that were not used. The nesting palms in the healthy TRC swamp were significantly taller than the nesting palms in the managed TRC swamp and the dieing BSNP swamp. DBH among the nesting palms in the three sites did not differ. In 1995, three pairs of red-bellied macaws and two pairs of blue-and-yellow macaws nested in the cut palms in the managed TRC swamp. Nest success was 50% and fledging 0.50±0.52 chicks per nesting attempt, nearly identical to previous work in Tambopata where success was 53% and 0.53±0.51chicks fledged per nest.

Concusions: Sustainable management of Mauritia flexuosa palm swamps for nesting macaws would require a rotation long enough to allow palm regeneration. This study indicates that cutting five palms a year in perpetuity would produce a stand of about 20 dead palms used by six or more pairs of macaws annually. However, occupancy rates would depend on macaw density and density of natural nest sites. Such management could be conducted on a 100-year rotation in an area of 1–4 ha or more depending on the palm density. Cutting natural palm swamp to provide a tourist attraction may not be acceptable or pertinent in all cases. However, a macaw colony could generate conservation benefits and an income through ecotourism. The macaws in this study usually defended nest sites from July or August and most chicks fledge by April, so managed swamps could have macaw activity, hence viewing opportunities, for up to 10 months per year.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://springerlink.metapress.com/content/f8unn51u13714652/fulltext.pdf

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