Fig. 3 Model validation and transferability for modelled species (A-J). Matrix values describe predictive accuracy via area under the receiver operator characteristic curve (AUC); AUC values (0-1) have been multiplied by 100 to save space. Reading by row shows how well each model trained on colony-specific data predicts foraging habitat suitability at all other colonies, reading by column shows how well foraging habitat suitability at each colony is predicted by models trained with data from all other colonies. Row names denote each colony-specific model and the multi-colony model. The ‘MEAN’ column gives global transferability of each colony-specific model and the multi-colony model by averaging the predictive ability across all colonies in the row (excluding the self-prediction value in colony-specific models). Local prediction is compared between colony-specific model self-prediction (diagonals) and multi-colony models (bottom row) by colour of AUC value: green shows model is better than the other; red shows model is worse than the other; black shows models are comparable (AUC values within 0.05 of each other). AUC value background colour denotes performance: grey (no better than chance/very poor); yellow (poor); light orange (moderate); dark orange (good); red (excellent). Dendrograms show clustering of pairwise colony AUC values; closely clustered colonies predict one another better. Family group models (B, C & G) have species codes added to colony names: CRTE = crested tern, CATE = caspian tern, ROTE = royal tern, LENO = lesser noddy, BLNO = black noddy, BRNO = brown noddy, GRFR = great frigatebird, LEFR = lesser frigatebird, MAFR = magnificent frigatebird. All colonies in the family group model for tropicbirds (H) represent red-billed tropicbird, with the exception of the Ashmore Reef (Australia) colony, which is red-tailed tropicbird (denoted with *).

Tropical seabird foraging radii

When considering all species and colonies, foraging radii ranged from 28.4 to 1166.2 km (Table 3). By increasing foraging range, modelled species were generally ordered: terns, brown booby, noddies, masked booby, wedge-tailed shearwater short trip, red-footed booby, tropicbirds, sooty tern, frigatebirds, wedge-tailed shearwater long trip. We found that the global foraging circle for each species contained a high percentage (89-100%) of known foraging areas from each tracked colony (Table 3).

Validating foraging circle refinement

We found an average of 89% of known foraging areas were included within refined foraging circles when using transferability-supported refinement of global foraging circles around each colony from our tracking dataset (Fig. 4). Our AUC-percentile scaling was effective at limiting the exclusion of erroneously predicted foraging habitat in poorer transferability models giving 80-99% known foraging area inclusion when the 45th percentile of habitat suitability or below, was used to delimit refined foraging circles. For refined foraging circles delimited with habitat suitability above the 45th percentile, our scaling maintained known foraging area inclusion at ~80%, showing that greater foraging circle refinement was effectively offset by the more accurate prediction of foraging habitat by higher transferability models.
Simulating increasing refinement of global foraging circles around each colony from our tracking dataset demonstrated that in the absence of transferability-supported refinement, refined foraging circles delimited by less transferable models always had a lower probability of including known foraging areas than those delimited by more transferable models (Interaction between percentile of foraging habitat suitability and model transferability: χ21 = 100.1, p < 0.001; Fig. 4). Simulation results for individual modelled species demonstrated the same pattern but there were differences between species due to ecology and sampling effort (Table 4, visualised in supporting information). Inclusion of known foraging areas in global foraging circles set the baseline probability for inclusion prior to refinement and differed between species (e.g. high in frigatebirds, low in sooty terns – despite similar foraging ranges; Tables 3 & 4). The steepest declines in known foraging area inclusion with foraging circle refinement were seen in masked and brown boobies and tropicbirds, whereas terns retained the highest inclusion of known foraging areas under refinement because their multi-colony model had good global transferability. Improving model transferability gave the greatest boost to inclusion of known foraging areas within refined foraging circles in tropicbirds, brown booby, sooty tern and masked booby, whereas frigatebirds known foraging area inclusion was least affected by model transferability (Table 4). The noddies model did not include the interaction term with transferability as all multi-colony model predictions were below 0.5 AUC.