Black-fronted terns and banded dotterels : causes of mortality and comparisons of survival : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand

1Il Abstract 1. The braided rivers of the South Island, New Zealand, provide feeding and breeding habitat for a range of endemic bird species. Many of these species are entirely reliant on braided river habitat for breeding, but becau e of a reduction in habitat quantity and quality due to weed infestation, hydroelectric power development and water abstraction, and high predation rates by introduced mammals, the survival of many of these bird species is under threat. 2. Predation is the primary cause of mortality for most braided river bird species, but most studies have only measured the effects of predation at the egg stage. In this study, I monitored breeding success of banded dotterels (Charadrius bieinetus) and black­ fronted terns (Sterna albostriata) on the Ohau River, South Island, from 1 998-2000, and examined the effects of predation on both species . The black-fronted tern is an1. The braided rivers of the South Island, New Zealand, provide feeding and breeding habitat for a range of endemic bird species. Many of these species are entirely reliant on braided river habitat for breeding, but becau e of a reduction in habitat quantity and quality due to weed infestation, hydroelectric power development and water abstraction, and high predation rates by introduced mammals, the survival of many of these bird species is under threat. 2. Predation is the primary cause of mortality for most braided river bird species, but most studies have only measured the effects of predation at the egg stage. In this study, I monitored breeding success of banded dotterels (Charadrius bieinetus) and black­ fronted terns (Sterna albostriata) on the Ohau River, South Island, from 1 998-2000, and examined the effects of predation on both species . The black-fronted tern is an endangered species about which very little is known, so I also investigated aspects of its breeding biology. 3. I used time-lapse video cameras at 39 nests of banded dotterels and determined that nest monitoring did not affect nest survival rates, nor do predators use human scent trails to locate nests . I attached radio transmitters to 49 banded dotterel chicks to assess rates and causes of mortality, but although a minimum of 1 8% of chicks were killed by predators, the transmitters did not provide information on the relative importance of the different predator species. Hatching success at 338 banded dotterel nests was 68%, and 48% of hatched nests fledged at least one chick. 4. Hatching success for 1 022 black-fronted tern nests was 50.2%, and a minimum of 27.6% of 897 chicks survived through to fledging. Cause of mortality was assessed for 1 48 chick, juvenile and adult terns, and I found that predators were responsible for 47% of deaths. Feral cats (Felis eatus) and Norway rats (Rattus norvegieus) were probably responsible for 1 9% and 5 1 % of predator related deaths, respectively. Mortality rates remained high immediately after fledging because of predation. Annual adult mortality was estimated at 88-92% but the associated confidence intervals were wide (57-99%). I document aspects of black-fronted tern ecology such as incubation period, fledging period, egg and chick weights, and develop a preliminary method for sexing adult black-fronted tern based on body measurements. I measured black-fronted tern chick growth and survival and found that hatching asynchrony results in lower growth and survival in second hatched chicks. I collated all existing data on black-fronted tern