Trinidad survey shows higher adult survival rates for tropical birds

Trinidad bird

Almost 4,000 birds have been captured and ringed across three sites in Trinidad

Trade-offs between characteristics such as survival and reproduction are central to life history theory, and the small clutch sizes seen in tropical birds may be offset by a longer lifespan and hence more broods. Studies of bird populations in Trinidad show an annual adult survival rate of two thirds (65%) which is higher than generally seen in equivalent temperate species.

The island of Trinidad, which in geological terms split relatively recently from Venezuela, boasts a rich avifauna of over 400 bird species, many of which are also found on the South American mainland. Life histories of tropical birds are generally less well understood than those of their temperate counterparts, principally because there have been very few tropical studies of sufficient length.

Three survey sites at different altitudes

Trinidad birdSince 2008 students from Dundee University have studied bird populations at three different sites in Trinidad, which will eventually augment 14 years of data taken from the same locations between 1986 and 2004 to form a virtually unique data set on tropical bird survival and other life history characters. The long research period encompasses a time of mass landscape change driven mainly by deforestation programmes for agriculture and limestone quarrying, and our data may also show how such disturbance has affected the structure and survival of forest bird communities. Our three sites occur at different altitudes in the Northern Range of Trinidad, each characterised by a distinct vegetation type and supporting a characteristic bird community.

Birds were caught using 18m long mist nets set at ground level from dawn, and checked frequently to prevent injury and mortality. Between five and eight nets were used for two or three consecutive days at each site, ensuring a constant sampling effort of 16 ‘net days’ per site.

Through longer adult survival, tropical birds are able to trade off smaller clutch sizes than are seen in temperate birds of comparable size

This cycle was then repeated so two blocks of surveying were conducted at the three sites each year. Each bird was identified to species and, where possible, the age and sex of the bird determined. A BTO aluminium ring with a unique identifying number was attached to the tarsus of each new bird caught, enabling recaptured birds to be identified individually, and body mass and wing length measured before release.

Survival rates

Trinidad birdAlmost 4,000 birds from 85 predominantly passerine species have been ringed across the three sites over the course of the present study, with nearly 1,000 more recaptured. Initial analyses of 18 of the bird species abundantly represented in the recapture data indicate that the mean adult annual survival rate is approx 65%, albeit with a high level of variation; ie roughly two-thirds of adult birds alive in a given year will survive to the following year. This corroborates estimates derived from previous datasets and lends support to the theory that, through longer adult survival, tropical birds are able to trade off smaller clutch sizes than are seen in temperate birds of comparable size.

Additional field seasons are planned in the coming years, allowing a more comprehensive understanding of the bird communities surveyed and providing a valuable scientific basis on which rainforest conservation policies can be based.

Written by

  • , University of Dundee and The James Hutton Institute, Dundee
  • , University of Dundee
  • , University of Dundee, The James Hutton Institute, Dundee and University of St Andrews
Twitter Digg Delicious Stumbleupon Technorati Facebook Email

No comments yet... Be the first to leave a reply!

Leave a Reply