Begin by setting up your environment. Ensure you have Python installed on your system, as it will be used to interact with both the Guardian API and DuckDB. Install DuckDB’s Python package using pip: `pip install duckdb`.

To access the Guardian API, you need an API key. Register on the Guardian Developer website and navigate to the API section to obtain your key. This key will authenticate your requests.

Use Python’s `requests` library to send a GET request to the Guardian API endpoint. Construct the API request URL, including your API key and any necessary query parameters (e.g., search queries, filters). Parse the JSON response to extract the data you need.

```python
import requests

api_key = 'your_guardian_api_key'
url = f'https://content.guardianapis.com/search?api-key={api_key}'

response = requests.get(url)
data = response.json()
articles = data['response']['results']
```

Once you have the data, transform it into a format suitable for insertion into DuckDB. Typically, this involves creating a list of dictionaries or a Pandas DataFrame, where each dictionary or row represents an article with fields such as title, publication date, and URL.

```python
import pandas as pd

articles_list = [
{
'title': article['webTitle'],
'publication_date': article['webPublicationDate'],
'url': article['webUrl']
} for article in articles
]

df = pd.DataFrame(articles_list)
```

Initialize a DuckDB database file (or in-memory database if persistence is not needed) by using DuckDB’s Python interface. Create a connection to the database and prepare to insert data.

```python
import duckdb

conn = duckdb.connect('guardian_data.duckdb')
```

Define a table schema in DuckDB that matches the structure of your transformed data. Use SQL commands to create a table in the DuckDB database.

```python
conn.execute('''
CREATE TABLE IF NOT EXISTS articles (
title TEXT,
publication_date TIMESTAMP,
url TEXT
)
''')
```

Use the DuckDB connection to insert the data from your Pandas DataFrame into the DuckDB table. Leverage DuckDB’s ability to handle Pandas DataFrames directly for efficient data insertion.

```python
conn.execute('INSERT INTO articles SELECT * FROM df')
```

By following these steps, you can efficiently transfer data from the Guardian API to a DuckDB database without relying on third-party connectors or integrations.