Importance of Mangrove Forests in Peru

Importance of mangrove forests in Peru with notes on to undocumented species: Bare-throated Tiger-heron and Rufous-necked Wood-rail by Thomas Valqui and Barry Walker.

Resumen:

En el Perú se encuentra un área relativamente pequeña de manglar (0.1% con respecto al área total en el neotrópico), la cual se localiza en el límite sur de este ecosistema en el océano Pacífico. Esto podría llevar a pensar que su conservación sólo es de interés nacional. Sin embargo, en un análisis por país del número de aves especializadas en manglar, realizado en la costa del pacífico neotropical, notamos una homogeneidad que no guarda proporción con el área de manglar de cada país. Dada la rápida fragmentación a la que están siendo sometidos estos ecosistemas a nivel global y local, urge intensificar los conocimientos sobre aves de manglar así como intensificar nuestros esfuerzo por conservarlos. En este artículo documentamos la presencia de dos especies de aves en los manglares del Perú, que tendrían historias e implicaciones diferentes: Tigrisoma mexicanum tiene una población aislada en el manglar peruano a 1300 Km de su distribución conocida, mientras que Aramides axillaris habría estado expandiendo su distribución hasta alcanzar el manglar del Perú alrededor de los años 80. Estos registros deben insentivar la planificación de inventarios más detallados en los manglares peruanos y resaltan la importancia que esta pequeña área tiene a nivel global. Finalmente, recalcamos la necesidad e importancia de documentar correctamente la presencia de una especie nueva para determinada área o región, lo cual se puede lograr mediante una fotografía, una grabación acústica o un video.

Introduction:

Mangroves are susceptible to the same pressures of human encroachment and development that have resulted in significant losses of other wetland habitats. Because mangroves are generally located in coastal estuaries which are considered valuable real estate and provide prime habitat for shrimp, clams and other seafood products with high market values, they have suffered extreme degradation3,7. As a result, many large contiguous mangroves have been either completely destroyed or severely fragmented. Thus minimal patch size has become a major conservation issue in many areas7. In Peru, there are two extant patches of mangrove associated with the two major northern rivers that drain into the Pacific: the Tumbes and the Piura. The northern patch, consisting of 4,814 ha, of which 2,972 ha are officially protected, is located on the border with Ecuador between 03o24’S and 03o35’S in dpto. Tumbes. The southern patch consists of a 250 ha islet19 350 km further south at 05o30’S in dpto. Piura, and is not officially protected. These two patches with 5 064 Ha represent less than 0.1% of the between 5 and 7 million ha of mangrove in the neotropics6,20, and mark the southernmost limit of mangrove in the Pacific Neotropics. In general, relatively little is known about mangrove ecology3,7 and even less about the use of mangrove habitat by birds and their movements within and between mangroves. More than 120 species of birds 2,10,12,14,16 (plus our own data) have been recorded in mangroves in Peru. However, many of these records reflect only occasional, marginal or fringe use of this habitat. Few bird species recorded in Peruvian mangroves are dependent upon them and even fewer are true ‘mangrove specialists’. According to Parker et al.11 93 Neotropical bird species are thought to habitually use mangroves. Of these, 40 have been recorded in Peru, but only 24 (60%) have been recorded in Peruvian mangroves. The remaining 16 (40%) are known, in Peru, from other habitats, with 12 of them restricted to the eastern Andes where there are no mangroves. Thus, while these 16 may use mangroves elsewhere, they show no dependence on them in Peru. The reverse can also be true: a generalist that uses non-mangrove habitat elsewhere may be restricted to this habitat in Peru. For example, Bare-throated Tiger-heron Tigrisoma mexicana is not a true mangrove specialist but, in Peru, this species is apparently entirely dependent upon the existence of mangrove habitat (see below). Peru’s mangrove represents only a tiny fraction of the global area covered by this habitat, and, in consequence, the conservation of Peruvian mangroves may appear of minimal priority. Nonetheless, in a Neotropical context, Table 1 demonstrates the relative uniformity in the number of bird species supported by mangroves regardless of the available area of habitat. For example, Colombia possesses over 87,000 ha of mangrove15, or more than 15 times as much as Peru, but the number of additional mangrove-associated species in Colombia does not correspond to the sizeable difference in available habitat. Given that the number of mangrove-associated bird species does not appear positively correlated with available habitat size, conservation of Peru’s remaining mangroves should be a priority within strategies for mangrove habitat throughout the western Neotropics. Mangrove Black-Hawk Buteogallus subtilis is the only specialist to occur throughout mangroves along the Pacific coast of America. Costa Rica, Colombia and Ecuador (Galápagos) each possess an additional, endemic mangrove specialist (two hummingbirds and a finch). Table 1. Use of mangroves by Neotropical birds according to country (totals based on Parker et al.11). The last row comes from a single source20, since area estimates vary greatly from source to source.

Number of species that:

Neotropics

Mexico

Costa Rica

Panama

Colombia

Ecuador

Peru

use mangroves

93

37

42

44

55

42

40

primarily use mangroves

16

6

6

6

8

8

6

are restricted to mangroves

4

1

2

1

2

2

1

times the area of Mangroves in Peru20

--

--

8.1

17.3

15.7

5.7

1

Species accounts:

We provide the first published documentation of two species with rather different histories in Peru. One represents a possible range expansion and the other a small, previously overlooked population. These records also illustrate the paucity of knowledge and limited extent of information available on Peruvian mangroves, despite their restricted size and easy accessibility. Bare-throated Tiger-heron Tigrisoma mexicana: This species’ presence in the Peruvian mangroves was distinctly unexpected. Recent literature does not cite any occurrences even close to Peru. The first recent record we are aware of, comes from Sagot14 in the late 1990s. At the INRENA (Instituto Nacional de Recourses Naturales) park ranger station at El Algarrobo, Bare-throated Tiger-heron is depicted, with its correct scientific name, in a small display at the interpretation centre, and is well known to the park rangers who describe it as ‘uncommon’. An adult was photographed by TV in the mangroves of El Algarrobo on 24 August 1999. The bird was located along one of the estuary channels during a tour by the local fishermen’s association. It was perched on a trunk (see Fig. 1), above a channel, and moved only slightly upon approach. Subsequently an adult was observed by BW et al. on 6 May 2000, in the same area at El Algarrobo. It was standing with outstretched neck on exposed mud below overhanging mangrove vegetation at low tide. During the c.3-minute observation, the distinguishing features including the bright yellow, unmarked, bare throat were clearly seen. On approach it calmly walked into denser vegetation and disappeared. Bare-throated Tiger-heron occurs contiguously from Mexico south through Central America and barely reaches north-west Colombia1,4,5,8,13. The peruvian records represent a range extension of c.1,300 km. No records from intervening areas have been published in recent literature. However, 115 years ago, Taczanowski17 cited Tigrisoma cabanisi (=T. mexicana) from ‘Tumbez’, based on a male specimen taken by Antonio Raimondi. While the specimen has apparently been lost, the description includes unequivocal Bare-throated Tiger-heron characters, such as its resemblance to Fasciated Tiger-heron T. salmoni (=T. fasciatum) with a longer bill, paler overall coloration and the entirely diagnostic bare throat. This record has since been overlooked, apart from being mistakenly mentioned as a Tumbes record of Rufescent Tiger-heron T. lineatum2. Cook2 probably assumed that the latter species was more likely in Tumbes, despite its absence from the western Andes south of Colombia. Do these records, more than 100 years apart, represent vagrants or a small local population? The isolated nature of the records and lack of any pattern of vagrancy in the species8, suggests the presence of a local population. It is interesting to note that the species has recently only been recorded in the El Algarrobo mangroves and not at Puerto Pizarro, which has been more extensively covered by observers. The rarity of the species, its nocturnal or crepuscular habits8,13, and lack of intensive ornithological studies in Peruvian mangroves may account for the lack of records. Rufous-necked Wood-rail Aramides axillaris: Parker et al. (1995) were first to report Rufous-necked Wood-rail in Peru (from February 1986, July 1988) It has subsequently been repeatedly reported from the mangroves in Peruvian Tumbes, TV in July 1995 and August 1999, BW in May 1996, June 1999 and April 2000, Cook2, and many other observations. It was not listed in early accounts (e.g in 19829 and 198116) and in more recent literature it is listed as ‘undocumented’ in Peru18 due to the lack of published physical evidence, such as a specimen, sound recording or photograph. One was photographed by TV on 24 August 1999, during a visit to El Algarrobo when at least eight individuals were observed. It appears to be locally common around El Algarrobo and Puerto Pizarro, and has also been recorded by M. Kessler within the Tumbes Reserved Zone, away from mangroves in El Caucho in 198610. A singing bird was tape-recorded by BW on 20 January 2001 near Pozo del Pato21. The extension of this species’ range to the Peruvian mangroves and Tumbes Reserved Zone is unsurprising given that it is known from Mexico and Central America, through Colombia to south-west Ecuador, in mangroves bordering Peru 1,5,18. It is surprising that evidence of the species’ occurrence in the Peruvian Mangrove was not gained prior to 1988. Many individuals and scientific parties have visited and collected specimens in the Peruvian mangroves before that12,16 and the species is now virtually guaranteed during any day trip to the mangroves at low tide. Conceivably the species is expanding southwards and only recently reached what appears to be its current limit in the Peruvian mangroves.

Conclusions:

Conservation of Peruvian mangroves is not only of local importance but of global interest. As mangroves are by nature narrow, linear and discontinuous strips on coasts, conservation of this habitat requires a very different approach from that demanded for other forested habitats in the Neotropics. Rather than searching for large, undisturbed areas, it may be of greater priority to adequately conserve as many healthy patches within its original distribution as possible, which could also benefit from the inclusion of adjacent non-mangrove woodland. In Peru, we consider it important to intensify surveys of mangroves to obtain complete inventories of the avifauna. These surveys should also include the small patch at San Pedro in Piura, which has received little ornithological attention and no protection. Finally we stress the importance of documenting new or rare species records: photographs, video recordings and sound-recordings, as opposed to sight records, can be objectively reviewed in the future and can therefore be considered as evidence. Given our still basic knowledge of many South American birds, the contribution that birdwatchers can make towards ornithology will be greatly increased if the means of obtaining such documentation be always kept at hand, especially when visiting remote or poorly known areas.