# Nest Depth and Height Are Associated with Breeding Outcomes in the Small Bee-Eater (Merops orientalis): A Preliminary Field Study from Pakistan

## TL;DR

This study found that nest depth and height in small bee-eaters are linked to better breeding outcomes, suggesting conservation should focus on preserving suitable nesting habitats.

## Contribution

The study provides new empirical evidence that nest structural traits, not surrounding habitat features, most strongly influence breeding success in small bee-eaters.

## Key findings

- Clutch size increased significantly with cavity depth in small bee-eaters.
- Breeding success was positively associated with nest height above ground.
- Nest structural traits explained more variation in reproductive performance than landscape features.

## Abstract

Small bee-eaters excavate nest cavities in open habitats, but little is known about the roles of cavity shape and surrounding habitat in their breeding ecology. In this study, we followed the fate of the eggs and chicks of the small bee-eater to determine whether cavity depth, entrance dimensions, nest height, and habitat in the vicinity (i.e., grasslands, farmlands, towns, or power lines) correlated with clutch size and reproductive success. We found that clutch size increased significantly with cavity depth, indicating that deeper cavities allowed females to lay more eggs. Breeding success was positively related to nest height, whereas entrance diameter and habitat distance to grasslands, farmlands, towns, and electric wires had little or no correlation. These results show that nest structural features, particularly cavity depth and height above ground, play a stronger role in breeding outcomes than surrounding landscape features. Therefore, conservation efforts should prioritize the preservation of suitable nesting habitats and minimize human disturbance around active breeding areas.

Nest architecture and surrounding habitat features can strongly influence the reproductive success of cavity-nesting birds; however, quantitative data from natural environments remain limited. We examined how nest structure and surrounding habitat features correlate with reproduction in the small bee-eater (Merops orientalis). A total of 38 natural nests were monitored during the breeding season. The Conway–Maxwell–Poisson model showed that cavity depth was a significant positive predictor of clutch size (β = 0.46 ± 0.22 SE, p = 0.036), whereas entrance diameter and nest height were not significantly related. Principal component analysis (PCA) of standardized cavity dimensions (cavity depth, entrance diameter, and nest height) showed that nest height (captured by PC2) was strongly associated with higher breeding success (OR = 0.002, p = 0.021), whereas overall cavity size (PC1) had a weaker, marginally positive correlation (OR = 3.87, p = 0.09). Habitat distance variables showed only weak, non-significant trends after accounting for multicollinearity. Nest structural traits explained more variation in reproductive performance than landscape variables (pseudo-R2 = 0.80 for clutch size; 0.59 for breeding success). Field monitoring of 38 nests showed a mean clutch size of 3.9 eggs, an overall hatching success of 77.5%, and a fledging success of 51.2%, yielding a 37.1% breeding success. Our results highlight the importance of conserving sandy streambanks and mitigating human disturbance in proximity to active nests to conserve breeding success in small bee-eaters. As these findings were based on one site and a single breeding season, broader generalizations will require replication across additional years and locations.